Important notice
Dear Customer,
On 7 February 2017 the former NXP Standard Product business became a new company with thetradename Nexperia. Nexperia is an industry leading supplier of Discrete, Logic and PowerMOS
semiconductors with its focus on the automotive, industrial, computing, consumer and wearable
application markets
In data sheets and application notes which still contain NXP or Philips Semiconductors references, use
the references to Nexperia, as shown below.
Instead of http://www.nxp.com, http://www.philips.com/ or http://www.semiconductors.philips.com/,
use http://www.nexperia.com
Instead of sales.addresses@www.nxp.com or sales.addresses@www.semiconductors.philips.com, usesalesaddresses@nexperia.com (email)
Replace the copyright notice at the bottom of each page or elsewhere in the document, depending on
the version, as shown below:- © NXP N.V. (year). All rights reserved or © Koninklijke Philips Electronics N.V. (year). All rights
reserved
Should be replaced with:- © Nexperia B.V. (year). All rights reserved.
If you have any questions related to the data sheet, please contact our nearest sales office via e-mailor telephone (details via salesaddresses@nexperia.com). Thank you for your cooperation andunderstanding,
Kind regards,

Team Nexperia

AN11119
Medium power small-signal MOSFETs in DC-to-DC
conversion
Rev. 3 — 7 May 2013

Application note

Document information
Info

Content

Keywords

DC-to-DC converter, charge pump, buck converter, boost converter,
small-signal MOSFET

Abstract

This application note explores different methods of DC-to-DC conversion.
It includes some examples of DC-to-DC down-converters using
small-signal MOSFETs.

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Revision history
Rev

Date

Description

3

20130507

Corrected typo on page 13 (changed 0.68 H to 6.8 H)

220120705

Figure 24: changed1

20120504

Initial revision

Contact information
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

2 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

1. Introduction
In modern electronic designs various supply voltages need to be generated. In mostcases power supply provides one or a few different DC voltages. These voltages need tobe converted to another voltage for several functional units in the application. Voltage
conversion can work in both directions: it can be step up or step down. This applicationnote presents different methods of DC-to-DC conversion.
Using linear voltage regulators for voltage conversion was common, even if a voltage had
to be reduced significantly or if the load currents were high. Because linear voltage
regulator works as a controlled series resistor, a lot of energy is dissipated thermally.
Due to the environmental requirement to improve energy efficiency of electronicequipment, Switch mode power supplies are replacing linear voltage regulators. In Switch
mode power supplies, energy is stored in the magnetic field of inductors or as a charge incapacitors. Ohmic loss of energy has to be avoided as much as possible.
Newly developed electronic components for implementation of switches, such as modern
MOSFETs, support design of highly efficient power supplies. Small-signal MOSFETs withlow drain-source on-state resistance RDSon values and good switching performance open
a new application area for medium power Switch mode DC-to-DC conversion. Although
fully integrated solutions are available, applications with external switching stages arewidely used due to flexibility and cost reasons.

2. DC-to-DC conversion methods
2.1 Linear voltage regulation
Although Switch mode power supplies are replacing linear voltage regulators, there aremany application areas where this approach is still used. Linear voltage regulators arefound where the output voltage needs to be free from switching ripple and overlaid
distortion. Supply for analog-to-digital converters (ADC) and digital-to-analog converters(DAC) and analog circuit parts with high signal-to-noise requirements are good examples.
Often such stabilizers are put behind Switch mode voltage converter to achieve a very
clean output voltage for the circuit block behind.
Figure 1 presents simple circuit diagram for voltage stabilizer. The output voltage is:
V OUT = V Z – V BE

(1)where VZ is Zener voltage and VBE is base-emitter voltage of transistor T1.
The transistor has total power dissipation:
P tot =  V IN – V OUT   I load + V BE  I B(2)

The first part of the addition contains dominating part of the losses. It increases with
voltage difference from the input to the output and the load current. In this circuit example,
an NXP Semiconductors low collector-emitter saturation voltage VCEsat transistor isapplied. It offers high and constant gain amplification. This means low dependency on DC
current gain hFE versus collector current and the advantage of low VCEsat.
AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

3 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

This design is beneficial because it keeps voltage drop across the regulator as small as
possible. Linear voltage regulators that need low voltage on top of the output voltage forproper stabilization are called low dropout regulators (LDO).
Along with minimum dropout voltage, the quiescent current Iq is an important parameterwith respect to the energy efficiency. This parameter defines the current that flows into thecircuit when no load is present.
I q =  V IN – V Z   R1

(3)

A circuit example:

Fig 1.

Simple linear voltage regulator with Zener diode and BISS transistor in the loadpath.

If requirements for quality of the line and load regulation are high, more sophisticatedcircuits need to be used. These contain voltage reference with high temperature stability
and more precise feedback control with an error amplifier.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

4 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Fig 2.

Linear voltage regulator with a TL431BFDT as an error amplifier

Figure 2 shows an example using TL431BFDT shunt regulator as an error amplifier withan external series load regulation transistor.
For additional features such as protection against thermal damage and current limitation,
typical choice is an integrated regulator. An example of such a device is NX1117.
Maximum nominal output current is 1 A. Dropout voltage is the difference between VINand VOUT. Maximum dropout voltage of NX1117 is 1.2 V for 800 mA load current.
LDOs specifications contain additional key parameters. Line regulation parameter shows
output voltage change in response to input voltage change. Output regulation statesstability of the output voltage for different load currents, for example 0 mA versus 800 mA.
Ripple rejection indicates reduction of a ripple after rectification achieved with Graetz
bridge and a capacitor added at the output. Therefore this parameter is measured for
120 Hz sine wave overlaid onto input voltage. This is a scenario adapted to 60 Hz line
supply system. An additional parameter is stability of the output voltage versus
temperature and spread of nominal output voltage for an LDO at a nominal operating
point.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

5 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Figure 3 shows a simple example with adjustable version of NX1117. VOUT can becalculated as:
R2
V OUT = V ref  1 + ------- + I adj  R1

R1

(4)

Adjust current Iadj is typically 50 A for NX1117 and therefore the second term can beneglected. Reference voltage Vref is 1.25 V for the adjustable NX1117. In addition toadjustable type many regulator types with fixed output voltages are available. In this case,the reference pin is connected to the ground and divider with R1 and R2 is integrated.
The dissipated power of fixed regulator is:
P tot =  V IN – V OUT   I OUT + V IN  I GND

VIN

(5)

NX1117CADJZ

VOUT
R1

R2

Fig 3.

AN11119

Application note

Adjustable linear voltage regulator NX1117CADJZ

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

6 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

2.2 Voltage conversion with a charge pump
In some applications, a simple voltage inversion or a doubling of voltage is required.
Sometimes only a low current is needed. An example of such application is generation ofnegative voltage for operational amplifier or comparator or boosted voltage for high-side
switch of a buck converter. The latter topology is discussed in more detail further in thisdocument. Usage of charge pumps is a common method of DC-to-DC conversion withoutdisadvantage of generating large losses. Charge pumps use capacitors for energy
storage. The principle is that a capacitor is charged and then shifted up or down to obtaina higher voltage or to get an inverted voltage.
Figure 4 shows an example of such circuit on condition of ideal diodes without forward
voltage loss. A generator is providing a square wave signal. It delivers a signal with lowlevel of 0 V and high level of VIN. If the generator outputs a high signal, C2 is charged.
When the generator output switches to the ground, the positive pole of the capacitor isconnected to the ground. Due to the charged capacitor, the node where C2 is connectedto the cathode of D4 and the anode of D2 has a voltage level of VIN. The diode D4
becomes conductive and C4 is charged to negative voltage. VOUT2 becomes inverted VIN
after a few cycles.

Fig 4.

Charge pump diagram with inverted and doubled output voltage

When the output of the generator is at low level, C1 is charged to VIN via D3 through theupper signal path. Also C3 gets charged to VIN via D3 and D1. When the output changes
to the high state, the negative pole of the charged capacitor is shifted up to VIN. Capacitor
C3 is charged to double VIN in the ideal case after a few switching cycles.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

7 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

In practice, forward voltage of diodes reduces output voltage. This means that output
voltage of the discussed voltage doubling is decreased by twice VF compared to losslessand ideal condition.


9
9
























WLPH PV

(1) VOUT(2) VINFig 5.

Voltage doubling with a charge pump, BAT54 Schottky diodes

Figure 5 shows simulation result for the start-up of voltage doubling with charge pump and
BAT54 Schottky diodes. The input voltage VIN is 5 V, capacitor C1 is 22 F and C3 is
10 F. The load is 1 k. The trace shows that theoretical output voltage of 10 V is notreached. If such a circuit has low supply voltage, forward voltage losses of diodes becomea significant problem. In order to improve it, switches, which are usually implemented with
MOSFETs, can replace diodes.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

8 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

2.3 Topologies of voltage converters with inductances
Application areas of charge pumps described in previous chapter are usually limited to
low current applications. For higher output power and highly energy-efficient voltage
converters, the best solution is topology with inductors. With a small topology modification
down-, up- and up-down converters can be implemented.

2.3.1 DC-to-DC down-converter
Figure 6 shows the circuit diagram of a simple DC-to-DC down-converter. In contrast to alinear regulator, this circuit would have 100 % efficiency in case of ideal components
application. In practice, there are losses in switching transistor because the on-resistanceis not equal to 0 and also because transistor needs switching time, which introduces
switching losses. Other components add losses too. Inductor has an ohmic resistancefrom the wire of the windings and magnetic core adds losses too. Magnetic core losses
result from the change of the magnetic field which causes motion of small magnetic
domains. The bigger the hysteresis of the core material, the bigger are these losses. Eddy
currents cause further loss in the magnetic core of an inductor. Changing magnetic fields
can induce circulating loops of current which heat up the ferromagnetic material. For highfrequency switching, the current in the wire no longer uses the whole cross-section,
instead it concentrates closer to the surface. This is a well-known skin effect which leads
to higher ohmic losses.
Also the output capacitor has a residual resistance that leads to energy losses and atemperature increase. Finally, the diode introduces forward voltage losses and reverse
current losses. These mechanisms and facts reduce the energy efficiency of DC-to-DC
converters from 75 % to 98 % in real life conditions.

Fig 6.

Simple DC-to-DC down-converter

The P-channel FET Q1 works as high-side switch. When the FET is switched on, thecurrent in the inductor L1 increases with a linear curve I L =  t on  L1    V IN  V OUT  ,VOUT is constant.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

9 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

When the switch is opened, the current continuously flows via the path of the diode D1.
The cathode of D1 is negative with the forward voltage VF against ground. The current
decreases linearly. C2 buffers the output voltage. The bigger it is, the smaller the ripple
will be.
Figure 7 depicts a SPICE simulation. The high-side switch is implemented with NX2301PP-channel FET. It works at the voltage supply V1. The inductance of the inductor ischosen to 68 H, the output voltage is filtered with 10 F capacitor. PMEG2010AEH
Schottky diode is selected as a free-wheeling diode. To control NX2301P, a N-channel
driver FET is implemented, which is switched from a square wave generator with 3.3 V
high level (V2). In this example, the switching frequency is 100 kHz. A load resistor of
10 is connected to the output.

Fig 7.

SPICE simulation diagram for a simple DC-to-DC down-converter using NX2301P
as high-side switch and PMEG2010AEH as low-side Schottky diode.

Figure 8 shows simulation result. The current IL1 which flows through the inductor shows alinear increase while Q1 is switched on. The voltage at SW node VSW nearly equals to the
input voltage. When Q1 is switched off, the current through the inductor decreases. The
signal SW changes to a negative voltage of about 300 mV, which is the forward voltage of
the Schottky diode. The output current is the average of the triangle shaped waveform
and is about 330 mA. The output voltage VOUT is stable at roughly 3.25 V.
In the abovementioned example, the current flows through the inductance for the whole
period of the switching cycle. This mode is called continuous mode of a DC-to-DC
converter. Below is a calculation of output voltage. The voltage at an inductor is:
V L = L   dIL  dt (6)orV L = L   I L   t 

AN11119

Application note(7)

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

10 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversionsoI L = V L  L  t

(8)

The stored energy in an inductor is:
E= L  2  I

2(9)For the Stationary mode while switch is closed, the energy increase in the inductor mustbe identical to the energy loss while switch is open.
Neglecting RDSon losses in the switch and the forward voltage of the diode, we get theformula for ∆IL:
I L =  V IN – V OUT   t on = V OUT  t off(10)

V OUT  V IN = t on   t on + t off  = t on  T(11)where T is cycle time and the duty cycle D is:
D = t on  T(12)

V OUT = V IN  D(13)In our example:
V OUT = 4 ,5 V   7 ,2  10  = 3 ,24 V(14)

If the duty cycle is 1 as a corner case, the switch is always closed and the output voltage
equals the input voltage. If the duty cycle is smaller than 1, the output voltage is reducedby factor D.
The ripple of the current is:I L =  V IN – V OUT   L  t on

(15)

In our example:
I L =  4 ,5 V – 3 ,24 V   68 H  7 ,2 s = 133 mA

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013(16)

© NXP B.V. 2013. All rights reserved.

11 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion







9
9

,/
P$





































WLPH PV

(1) VSW(2) VOUT(3) IL1

Fig 8.

Curves of the current through L1, SW node voltage and output voltage

If the load current is increased in the continuous mode, the output voltage stays constant(ideal components) . This means that duty cycle for the switch does not need to bechanged to a significant extent from a DC-to-DC controller IC as long as the converter
runs in the continuous mode. There is a current limit where the continuous mode is left.
A relevant equation is below:
I L = 2  I L  average  = 2  I load

(17)

If curve 3 on Figure 8 moves down by decreasing the output current until the x-axis is
touched, the limit of the continuous mode is reached. From this point onward the duty
cycle has to be reduced in order to keep the same output voltage.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

12 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

If non-continuous mode is reached, the voltage curve of SW node of the circuit changes
significantly. Normally there is roughly a square wave between VIN and VF. If the current
through the inductance reaches 0 A, the voltage at the diode changes from forward
direction to reverse. The diode blocks the output capacitor, which is charged to VOUT frombeing discharged via L1 (Q1 is still closed). After the current through L1 went down tozero, SW node shows an oscillation supported by the resonance circuit of L1 and COUT.
Figure 9 shows this typical behavior. Circuit on Figure 7 was modified by reducing theinductance of L1 to 6.8 H for this experiment. This leads to a higher current ripple, and a
non-continuous mode.





9
9

,/
$



































WLPH PV

(1) VSW(2) VOUT(3) IL1

Fig 9.

Converter in a non-continuous condition, current curve of IL reaches thex-axis at 0 A, curve of SW node jumps from VF to an oscillation around VOUT

Figure 10 shows a change in the down-converter topology to improve efficiency of thesimple circuit. The Schottky diode generates forward voltage losses for the time period
when high-side switch is opened. A MOSFET can replace a diode. The low-side switch
needs to be turned on when the upper FET is switched off. The controller has to take carethat there is never an overlap of the on-states of both transistors in this case the switchingstage would create a short circuit with a significant current peak, high losses and risk todamage the FETs. Because every MOSFET contains a body-diode from the source to thedrain, the circuit would in principle work even if Q2 is never switched on. In this case, thebody-diode of Q2 would work like a Schottky diode in the simple topology on Figure 6.
Therefore the turn-on time of Q2 is not very critical. If Q2 switches on after Q1 is closed,
the body diode conducts the current from L1.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

13 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Fig 10. Synchronous DC-to-DC down-converter (FETs including body-diodes)

2.3.2 DC-to-DC up-converter
In the previous chapter, inductor-based DC-to-DC down conversion was discussed. Witha small change in the topology, the down-converter can be changed into an up-converter.
Figure 11 shows the topology of a simple DC-to-DC up-converter. If the low-side switch
FET Q1 is closed, the current in the inductance increases:
I L = V IN  t on

(18)

The diode D1 is driven in reverse mode because the anode is connected to the groundand the cathode is connected to the positive voltage VOUT at C2. If the switch is closed,
the current IL continues to flow through D1 into the output. If the converter runs in astationary mode, we can calculate:I L = V IN  L  t on =  V OUT – V IN   L  t off(19)

V IN  t on =  V OUT – V IN   t off(20)

V OUT = V IN   t on  t off + 1 (21)

where the duty cycle is:
D = t on  T(22)

T = t on + t off(23)

V OUT = V IN   t on + t off   t off = V IN  T   T – t on 
= V IN  1   1 – t on  T = V IN  1   1 – D 

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013(24)

© NXP B.V. 2013. All rights reserved.

14 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

The corner cases of the equation show that for D  0, which means that the transistor isnever switched on, VOUT  VIN. It makes sense to consider lossless components. Losslessmeans a diode with no forward voltage and an inductance without an ohmic resistance of
the windings and the additional loss mechanisms discussed in the previous chapter. If D
gets close to 1, the output voltage increases rapidly. This is critical for safe operation
because high duty cycle can result in very high voltages at the FETs drain.

Fig 11. Simple DC-to-DC up-converter

Figure 12 shows SPICE simulation. The low-side switch is implemented with PMV20XN
N-channel MOSFET in SOT23 package and PMEG2010AEH Schottky diode. The
converter is switched with 100 kHz signal control signal with a duty cycle of 0.5.

Fig 12. SPICE simulation diagram for a simple DC-to-DC up-converter with PMV20XN
N-channel FET and PMEG2010AEH Schottky diodeAN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

15 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Figure 13 shows simulation results. Curve 2 represents output voltage. For ideal
components, the output voltage would be twice as high as the input due to the duty cycleof 0.5. In practice, the forward voltage of the diode reduces the output voltage. Curve 1
shows drain voltage VD of the N-channel FET. It switches between ground level andVD(max) and equals:
V D  max  = V IN  1   1 – D  + V F(25)

In the simulated case with the duty cycle D  0.5,

V D  max  = 2  V IN + V F

.





9
9

,/
$










































WLPH PV(1) VD(2) VOUT(3) IL1

Fig 13. Simulation results, simple up-converter

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

16 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Similar to DC-to-DC down-converter, energy efficiency of the up-converter also can be
improved if the Schottky diode is replaced by a FET, which switches on for the correct
phase in the switching cycle. Figure 14 shows the topology of synchronous DC-to-DC
up-converter.

Fig 14. Synchronous DC-to-DC down-converter

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

17 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

2.3.3 DC-to-DC up- and down-converter
If two topologies of the DC-to-DC down-converter and up-converter are combined asshown on Figure 15, the output voltage can either be reduced or boosted in relation to the
input voltage. The MOSFET switches need to be controlled in a proper way to allow theconversion in both directions. Q3 and Q4 can switch similarly to the DC-to-DC
down-converter shown on Figure 10. In addition, Q2 must be switched on constantly toconnect the inductor to the output capacitor. For the up-conversion mode, MOSFETs Q2
and Q1 work as the switching stage, as described for the synchronous up-converter on
Figure 14. The MOSFET Q3 is constantly switched on to connect the inductor to the input
supply voltage in this case.

Fig 15. Up-down converter

3. Medium power DC-to-DC down-converter using small-signal MOSFETs
3.1 DC-to-DC down-converter application board
Figure 16 shows an application Printed-Circuit Board (PCB) with NXP Semiconductors
small-signal MOSFETs implemented in a DC-to-DC step-down converter. NXP
Semiconductors offers small-signal MOSFETs in small SMD packages such as SOT457,
SOT23, SOT223 and DFN2020MD-6 (SOT1220). Many of these MOSFETs provide very
low RDSon together with a good switching performance.
The topology of the application board on Figure 16 is a synchronous down-convertersame as in Section 2.3.1. The circuit contains a controller LTC3851 of Linear Technology
Corporation. Two N-channel MOSFETs build switching stage. The high-side switch
connects the node with the inductor to the input supply. Therefore, it is necessary to havea control voltage available that is higher than the input voltage itself. This extra voltage forthe control of the gate of the upper MOSFET is generated with a charge pump. The
capacitor C25 is connected to the SW node, the switched output and via Schottky diode toa stabilized voltage INTVCC (pin 12). INTVCC is provided by an internal 5 V LDO. The
capacitor is charged via the diode when the low-side switch is turned on. In this case, oneside of C25 is connected to ground. If Q2 is turned off and Q1 is switched on, the charged
AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

18 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

capacitor gets connected to VIN. At the pin BOOST (pin 14) a voltage of
VIN  INTVCC  VF (forward voltage of the diode) can be measured. This boosted voltage
can drive the high-side switch properly. Low current Schottky diodes are sufficient for the
charge pump (for example, BAT54J, 1PS76SB40 or 1PS76SB21). These diodes aresupplied in the SMD packages like SOD323F and SOD323.
The LTC3851 controller contains a 0.8 V precision reference voltage for the output voltage
regulation. The output of the down-converter is fed back to the pin FB. A resistor divider
formed by R41 + R39 and R38 adjusts the output voltage.The equation for the output
voltage is:
V OUT = 0 ,8 V   1 +  R41 + R39   R38 (26)

The controller works with a constant frequency. As described in Section 2.3.1, the output
voltage of DC-to-DC down-converter can be controlled rather easily for higher currents,
but low current conditions are more ambitious for the control. The duty cycle needs to bechanged significantly or the controller can change to a different control mode like burst
operation. For the LTC3851 there are three options: forced continuous operation, burst
mode operation and a pulse-skip mode.
Burst mode operation gives better efficiency, but more ripple and a higher
ElectroMagnetic Interference (EMI) level. The best mode depends on the specification
and requirements of the end application.
The switching frequency can be programmed in a range from 250 kHz to 750 kHz. The
resistor R30 determines the frequency. Alternatively the controller can synchronize theinternal oscillator to an external clock source (MODE/PLLIN, pin 1). In this mode an RC
network needs to be connected to pin 2 (FREQ), which serves as PLL loop filter.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

19 of 33

xxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxx x x x xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx xx xx xxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxx xxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxx x xxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxx xxx

NXP Semiconductors

AN11119

JP2
1
2
3

C22

VIN
1

C19
1u0

100pF
JP_MODE
1
2
3
4

GND
INTVCC
FREQ
1

GND

RUN

C23

2

RUN

3

TK/SS_2

4

opt

5
6

GND

7

C30
1

TK/SS

R32

8

MODE

SW

FREQ

TG

RUN

BOOST

TK/SS

VIN

ITH

INTVCCFBBGSENSESENSE+

GND
ILIM

C25
100n

16

Q1

10µ

0

R37

1

GND
RSENSEINTVCC

1

COUT3

Q2
PMPB20EN

47u

D1

C27
10

PMEG3010ER
2u2

9

C31
4u7

IC1
GND R42

100n
R35

0

GND

R27
na

GND

COUT2

COUT1

330u

330u

GND

GND

GND

GND_OUT

R29

1

na
C18
GND

GND
na

R28
opt

opt
GND
SENSE+
C26
2n2
C28

R38
49k9

C29

C32

22p

opt

R39
43k2

330p
R40
6k8

R41
0
VOUT

GND

SENSE-

GND
R43
na

R10
10

VOUT

3.6 mOhm

11

1n
C24

GND

D2

10

12

GND

IHL-5050EZ-01-Coil
L1

BAT46WJ

R36

13

GND

PMPB20EN

15
14

GND

R9
10

GND

Fig 16. Circuit diagram for reference application of DC-to-DC down-converter with NXP Semiconductors small-signal MOSFET PMN15UN and
LTC3851 as controller

AN11119

20 of 33

© NXP B.V. 2013. All rights reserved.

Medium power small-signal MOSFETs in DC-to-DC conversion

Rev. 3 — 7 May 2013

All information provided in this document is subject to legal disclaimers.

0
TK/SS

CIN3

CIN1

GND_IN
1

1
2
3

JP_RUN

CIN4
10µ

LTC3851EPN

CIN2

+

82k5

GND

1nF

+

C21

+

10k

GND

R31
100n
R30

+

C20

GND

Application note

1

MODE

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

3.2 NXP Semiconductors small-signal MOSFETs suitable for DC-to-DC
conversion
DC-to-DC converters can be found in many applications. Topology of step-down converter
controller with an external FET stage are often implemented in computing and consumer
applications. Modern concepts with latest generation SOC (System-on-Chip) solutions
require many separate supply voltages. These can be processors on motherboards, innotebooks and tablet PCs, on core chips of LCD-TV or a set-top box.
The power requirements range from more than hundred watts down to a few watts. In
desktop PCs, DC-to-DC converter can be found on the motherboard which provide acurrent capability of up to 100 A and an output power of up to 130 W. MOSFETs inswitching stages are Loss-Free Package (LFPAK) types and to a growing extent Quad
Flat-pack No-lead (QFN) 5 × 6 packages. For net- and notebooks the power requirements
are smaller. The power consumption ranges from 18 W to 55 W. The switching MOSFETs
are mainly SO-8 and QFN 3 × 3 types. In consumer applications such as LCD-TVs andset-top boxes as well as in low-power netbooks or tablet PCs, power requirements from
7 W to 15 W can be found.
For medium power range small-signal MOSFETs can replace SO-8 versions nowadays insmaller packages like QFN 3 × 3, but also in QFN 2 × 2 or SOT457.

3.3 Dimensioning aspects for the inductor and output capacitor
In order to reach a desired current ripple, choose carefully inductance of the inductor usedin the down-converter. With a bigger current ripple, the output voltage shows a larger
ripple. The ripple increases the smaller the inductance becomes and the higher the input
voltage is. Furthermore it increases if the switching frequency is reduced.
IL can be calculated:
I L = V IN  L  t on = V OUT  L  t off

(27)

with:
T = t on + t off = 1  f(28)

we get:I L =  V OUT  L    1 – V OUT  V IN   1  f(29)

this means:
L =  V OUT  I L    1 – V OUT  V IN   1  f(30)

For the corner case in which circuit runs at the limit of the continuous mode, current goes
down exactly to zero before it increases again and we get simple relation:
I L = 2  I average

AN11119

Application note(31)

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

21 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Putting equasion 32 into the formula for IL:
L = V OUT   1 – V OUT  V IN   2  I average  f(32)

In practice, the ripple current IL is about 30 % of the maximum current, as a rule ofthumb.
The ripple of the output voltage does not depend on the chosen inductance and the ∆IL
only, but also on the capacitance of the output capacitor. The bigger the capacitor, thesmaller the ripple is. Figure 17 shows the waveform of the current into the capacitor. For alossless capacitor, there is basic equation:t2

1
Vc = ----   Ic  dt
C
to

(33)

Ic

t
t0

t1

ΔIL

ton

t2
toﬀ

Fig 17. Capacitor current IC versus time

For t0 to t1:
I C = I L  t on  t(34)

and for t1 to t2
I C = I L  t off  t(35)

the integral formula for the capacitor ripple voltage can be written as:
ton-------2

1
V Cpeak = ---C

Application note

I L

 t dt + ----  --------  t dt
  -------t on C   t off 
0

AN11119

I L

toff--------2

1

0

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013(36)

© NXP B.V. 2013. All rights reserved.

22 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

With:
T = t on + t off = 1  f(37)

the result is:
V C _ripple = I L   C  8  f (38)

For real capacitors take into account an Equivalent Series Resistance (ESR). So we getan equation:
V C _ripple = I L   ESR + 1   8  f  C out  (39)

3.4 MOSFET losses calculation
For MOSFETs used as switches consider two loss processes. One is the ohmic loss
caused by the residual on-state resistor RDSon. The second loss process happens at theswitching transients. Because FETs are not ideal switches that can change from off- to
on-state or reverse without a small turn-over time.
The RDSon losses are also called I2R-losses and they can be calculated:2

2

P up _side _switch = D   I OUT    1 +    R DSon = V OUT  V IN   I OUT    1 +    R DSon(40)
with duty cycle:
D = t on  T(41)

The term 1+δ contains the temperature dependency of RDSon of a MOSFET. δ has
typically a value of: =  0 005  C    T j – 25C (42)

For the low side switch, there is a similar formula. Because synchronous FET isconducting while the high-side switch is closed, the I2R looses can be calculated with theequation:2

P low _side _switch =  1 – D    I OUT    1 +    R DSon =2

1 –  V OUT  V IN    I OUT    1 +    R DSon

(43)

Regarding the transition losses, only the high-side switch suffers from this mechanism.
The reason is that the implemented free-wheeling diode (D1 on Figure 16) is getting
conductive. It reduces the voltage over the synchronous FET to its small forward voltage
VF. If the circuit does not contain a free-wheeling diode, the situation is different: losses ofthe body diode need to be added to the RDSon losses of the FET. In general, efficiency
suffers from the higher VF and reverse recovery time of the body diode if there is nofree-wheeling Schottky diode implemented.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

23 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Fig 18. Diagram for switching behavior tests for MOSFET

Figure 18 shows a test circuit for the switching behavior of a MOSFET. The parasitic
capacitors from the gate to the source CGS and from the drain to the gate CDG aredepicted explicitly. Current source IG controlls gate. At the drain another current source isconnected towards VSS with a free-wheeling diode in parallel. As long as the FET isclosed, the current flows through this diode.
Figure 19 shows how the switching-on process looks like. If the current source IG is
switched on, voltage at CGS rises with a linear curve until gate-source threshold voltage
VGS(th) is reached. At this time a drain current starts to flow. This means that the FET
remains in the off-state during the time period t0.
During t1 the drain current increases. Also the gate voltage increases until VGS(pl) is
reached. VGS(pl) is commonly known as plateau voltage of a MOSFET. It is normally not
explicitly mentioned in data sheets, but it can be derived from the diagram gate charge
versus gate-source voltage which can be found in detailed data sheets. After the time
period t0 and t1, the charge is Q0 = V pl   C GS + C DS  .
In the next time period t2, the drain voltage decreases and gate-source voltage VGS stays
constant at VGS(pl). CDS gets charged in the reverse direction with the charge Q1 which is:
Q1 = V SS  C DS

(44)

CDS is similar to the Miller capacitance known from bipolar transistors and has asignificant impact on the switching performance of a MOSFET.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

24 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

During t3 the gate voltage increases again until the current source is stopped where thedesired maximum gate voltage is reached. The RDSon of the FET is reduced further. The
gate driver provides an additional charge Q2, which is:
Q2 =  V GS  t4  – V GS  pl     C GS + C DS 

(45)

The total charge follows the equation: Q G = Q0 + Q1 + Q2
This charge can easily exceed 100 nC for a power MOSFET. With the equation:
IG = QG  ts

(46)

the gate current can be calculated to achieve a switching time ts. Therefore, if smalltransition times are desired, in order to keep the switching losses small, apply powerfuldrivers to controll MOSFETs.
VGS

VGS(pl)VGS(th)

Q0

Q1

Q2

t

VDS
Vin

ID
t0

t1

t2

t3

t4

t

Fig 19. Turn-on process for MOSFET, VGS, VDS and ID curves

During the time t1, there is the full input voltage at the FET while drain current ID
increases. In the next time section t2, ID is constant while drain-source voltage VDS
decreases. The major switching losses occur during these two timw periods in theswitching process. Rather small losses during t3 are neglected. During t3 RDSon falls to
the minimum value that is reached when the final VGS voltage is reached.
Switching losses during turn-on occur in the time period t1 and t2. The most dominanttime is t2 where the gate voltage of the MOSFET remains at the plateau voltage V(pl). The
losses can be calculated as:
P SW  on  = V IN  I  2   t3 + t1   1  T(47)with the switching frequency of converter: f SW = 1  T
Turn-off behavior of a MOSFET is similar to the turn-on process. Total switching losses
can be summarized as:
P SW = V IN  1  T   I min  2  t on + I max  2  t off 

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013(48)

© NXP B.V. 2013. All rights reserved.

25 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Switching time depends on the current drive capabilities of the driver device and the gate
resistance of the FET. If we assume an identical drive current for turn-on and turn-off
event, switching time equals: t SW = Q G  I drive
For the LTC3851 tSW can be estimated roughly as follows. Rdrive is about 2 for thecontroller. The relevant voltage is driver voltage INTVCC V(th), so we get:t SW = Q G  R drive   V drive – V GS  th  (49)

4. NXP Semiconductors high-performance small-signal MOSFETs insmall packages
4.1 Low RDSon N-channel small-signal MOSFETs
NXP Semiconductors offers several small-signal MOSFETs which are suitable for a
medium power DC-to-DC conversion. PMN15UN reaches RDSon of 15 m for agate-source voltage of 4.5 V. This is a very small resistance for a SOT457 device which
outperforms comparable MOSFETs on the market. Due to the copper leadframe, a very
good thermal performance can be achieved for this relatively small package.
Table 1.

Comparison of low RDSon small-signal MOSFETs in different packages
PMT29EN

PMN15UNPMPB20EN

Package

SOT223

SOT457

DFN2020MD-6(SOT1220)ID(max)

6A

6.3 A

5.8 A

VDS

30 V

20 V

30 V

VGS

20 V

8V

20 V

RDSon(typ) (VGS  4.5 V) 29 m

15 m

20 m

24 nC

7.8 nC

7.2 nC

40 ns

6 ns

4.9 ns

8.3 W

1.75 W

8.33 WQG
tf (fall time)
Ptot (tsp25 oC)

For both small board space requirements and good thermal performance, 2 mm x 2 mm
DFN2020MD-6 (SOT1220) package is a very good choice. For medium power
requirements, MOSFETs of this type can replace power packages like DFN3030 or
SO8 (SOT96) packages.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

26 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Table 2.

N-channel MOSFETs in DFN2020MD-6 (SOT1220)

Type

VDS(max)

VGS(max)

ESD

RDSon(typ)(VGS  4.5 V)

PMPB12UN

20 V

 8 V-

12 mPMPB12UN

20 V

 8 V-

20 mPMPB10XNE

20 V

 12 V

2 kV

10 m

PMPB15XN

20 V

 12 V-

15 m

PMPB23XNE

20 V

 12 V

2 kV

23 m

PMPB16XN

30 V

 12 V-

16 m

PMPB13XNE

30 V

 12 V

2 kV

13 m

PMPB29XNE

30 V

 12 V

2 kV

29 m

PMPB33XN

30 V

 12 V-

33 m

PMPB11EN

30 V

 20 V-

12 m

PMPB20EN

30 V

 20 V-

20 m

PMPB40SNA

60 V

 16 V-

40 m

Thermal photograph on Figure 20 shows reference DC-to-DC converter PCB running withan output current of 6 A . It performs a voltage down conversion from 10 V to 1.5 V. Due tothe small duty cycle of 0.15, low side-switch has to dissipate a higher amount of energy
than high side switch. The temperature of this device is about 80 oC. Considering the ruleof thumb that junction temperature Tj is 5 to 10 oC warmer than the surface of the
package, Tj is below 90 oC in this test.

VIN 10 V
VOUT  1.5 V
IOUT  6 A
fSW 490 kHz

Fig 20. Thermal photograph of the DC-to-DC converter PCB with PMPB20EN

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

27 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

4.2 Measurements at the reference PCB with PMPB20EN switching stage
Figure 21 shows a scope curve of the falling edge measured for the SW signal, the outputof the FET switching stage. The load current was adjusted to 3.5 A. The output voltage is
3.3 V. Figure 22 depicts measurement result of the rising edge.

Fig 21. Falling edge measured at the output of the FET switching stage(Figure 16 SW node)Fig 22. Rising edge measured at the output of FET switching stage (Figure 16 SW node)

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

28 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Table 3.

Stability of the output voltage versus load current, FET stage 2 × PMPB20EN in
DFN2020MD-6 (SOT1220) package measured at power and sense contacts

Output load current

Output Voltage

0A

3.296 V

0.1 A

3.296 V

0.5 A

3.295 V

1.0 A

3.295 V

2.0 A

3.294 V

3.0 A

3.294 V

4.0 A

3.293 V

6.0 A

3.292 V

5. Summary
Highly efficient medium power DC-to-DC converters can be designed with NXP
Semiconductors small-signal MOSFETs. This can be a simple converter with a P-channel
FET as high-side switch combined with a Schottky diode. For a Schottky diode NXP
Semiconductors offers a wide selection of components with low forward voltages incompact flat power packages. For even better efficiency, synchronous DC-to-DC
converters are recommended. Also for this topology NXP Semiconductors can offer
suitable small-signal MOSFETs in various packages.
This document describes the way of working of different DC-to-DC conversion topologies.
A reference design for synchronous DC-to-DC converter was presented with mostimportant design aspects, such as power dissipation in the switching stage.

6. Appendix
Figure 22 and 23 show the component placement plans of the DC-to-DC converter
reference board. The first figure shows component names whereas the second one
indicates component values. This PCB is a 4 layer board with top layer containing solid
copper areas which are connected to VIN, VOUT and ground. Layer 2 and the bottom layer
are solid ground layers. Layer 3 contains signal connections.

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

29 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Fig 23. Component placement plan of the DC-to-DC converter reference board withcomponent names

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

30 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

Fig 24. Component placement plan of the DC-to-DC converter reference board withcomponent values

AN11119

Application note

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

31 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

7. Legal information
7.1

Definitions

Draft — The document is a draft version only. The content is still underinternal review and subject to formal approval, which may result in
modifications or additions. NXP Semiconductors does not give any
representations or warranties as to the accuracy or completeness of
information included herein and shall have no liability for the consequences ofuse of such information.

7.2

Disclaimers

Limited warranty and liability — Information in this document is believed tobe accurate and reliable. However, NXP Semiconductors does not give any
representations or warranties, expressed or implied, as to the accuracy orcompleteness of such information and shall have no liability for theconsequences of use of such information. NXP Semiconductors takes noresponsibility for the content in this document if provided by an information
source outside of NXP Semiconductors.
In no event shall NXP Semiconductors be liable for any indirect, incidental,
punitive, special or consequential damages (including - without limitation - lost
profits, lost savings, business interruption, costs related to the removal or
replacement of any products or rework charges) whether or not suchdamages are based on tort (including negligence), warranty, breach ofcontract or any other legal theory.
Notwithstanding any damages that customer might incur for any reason
whatsoever, NXP Semiconductors’ aggregate and cumulative liability towards
customer for the products described herein shall be limited in accordancewith the Terms and conditions of commercial sale of NXP Semiconductors.
Right to make changes — NXP Semiconductors reserves the right to makechanges to information published in this document, including without
limitation specifications and product descriptions, at any time and without
notice. This document supersedes and replaces all information supplied prior
to the publication hereof.
Suitability for use — NXP Semiconductors products are not designed,
authorized or warranted to be suitable for use in life support, life-critical orsafety-critical systems or equipment, nor in applications where failure or
malfunction of an NXP Semiconductors product can reasonably be expected
to result in personal injury, death or severe property or environmental
damage. NXP Semiconductors and its suppliers accept no liability forinclusion and/or use of NXP Semiconductors products in such equipment orapplications and therefore such inclusion and/or use is at the customer’s own
risk.
Applications — Applications that are described herein for any of theseproducts are for illustrative purposes only. NXP Semiconductors makes norepresentation or warranty that such applications will be suitable for the
specified use without further testing or modification.

AN11119

Application note

Customers are responsible for the design and operation of their applications
and products using NXP Semiconductors products, and NXP Semiconductors
accepts no liability for any assistance with applications or customer productdesign. It is customer’s sole responsibility to determine whether the NXP
Semiconductors product is suitable and fit for the customer’s applications andproducts planned, as well as for the planned application and use ofcustomer’s third party customer(s). Customers should provide appropriate
design and operating safeguards to minimize the risks associated with theirapplications and products.
NXP Semiconductors does not accept any liability related to any default,
damage, costs or problem which is based on any weakness or default in thecustomer’s applications or products, or the application or use by customer’s
third party customer(s). Customer is responsible for doing all necessary
testing for the customer’s applications and products using NXP
Semiconductors products in order to avoid a default of the applications andthe products or of the application or use by customer’s third party
customer(s). NXP does not accept any liability in this respect.
Export control — This document as well as the item(s) described herein
may be subject to export control regulations. Export might require a priorauthorization from competent authorities.
Evaluation products — This product is provided on an “as is” and “with all
faults” basis for evaluation purposes only. NXP Semiconductors, its affiliates
and their suppliers expressly disclaim all warranties, whether express, impliedor statutory, including but not limited to the implied warranties of
non-infringement, merchantability and fitness for a particular purpose. The
entire risk as to the quality, or arising out of the use or performance, of thisproduct remains with customer.
In no event shall NXP Semiconductors, its affiliates or their suppliers be liable
to customer for any special, indirect, consequential, punitive or incidental
damages (including without limitation damages for loss of business, businessinterruption, loss of use, loss of data or information, and the like) arising out
the use of or inability to use the product, whether or not based on tort(including negligence), strict liability, breach of contract, breach of warranty or
any other theory, even if advised of the possibility of such damages.
Notwithstanding any damages that customer might incur for any reason
whatsoever (including without limitation, all damages referenced above andall direct or general damages), the entire liability of NXP Semiconductors, itsaffiliates and their suppliers and customer’s exclusive remedy for all of theforegoing shall be limited to actual damages incurred by customer based onreasonable reliance up to the greater of the amount actually paid by customer
for the product or five dollars (US$5.00). The foregoing limitations, exclusions
and disclaimers shall apply to the maximum extent permitted by applicablelaw, even if any remedy fails of its essential purpose.

7.3

Trademarks

Notice: All referenced brands, product names, service names and trademarks
are the property of their respective owners.

All information provided in this document is subject to legal disclaimers.

Rev. 3 — 7 May 2013

© NXP B.V. 2013. All rights reserved.

32 of 33

AN11119NXP Semiconductors

Medium power small-signal MOSFETs in DC-to-DC conversion

8. Contents
1
2
2.1
2.2
2.3
2.3.1
2.3.2
2.3.3
3
3.1
3.2
3.3
3.4
4
4.1
4.2
5
6
7
7.1
7.2
7.3
8

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
DC-to-DC conversion methods. . . . . . . . . . . . . 3
Linear voltage regulation . . . . . . . . . . . . . . . . . 3
Voltage conversion with a charge pump . . . . . . 7
Topologies of voltage converters withinductances . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
DC-to-DC down-converter . . . . . . . . . . . . . . . . 9
DC-to-DC up-converter. . . . . . . . . . . . . . . . . . 14
DC-to-DC up- and down-converter . . . . . . . . . 18
Medium power DC-to-DC down-converter using
small-signal MOSFETs . . . . . . . . . . . . . . . . . . 18
DC-to-DC down-converter application board . 18
NXP Semiconductors small-signal MOSFETs
suitable for DC-to-DC conversion . . . . . . . . . . 21
Dimensioning aspects for the inductor and output
capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
MOSFET losses calculation . . . . . . . . . . . . . . 23
NXP Semiconductors high-performancesmall-signal MOSFETs in small packages. . . 26
Low RDSon N-channel small-signal MOSFETs 26
Measurements at the reference PCB with
PMPB20EN switching stage . . . . . . . . . . . . . . 28
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Legal information. . . . . . . . . . . . . . . . . . . . . . . 32
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Please be aware that important notices concerning this document and the product(s)described herein, have been included in section ‘Legal information’.

© NXP B.V. 2013.

All rights reserved.

For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
Date of release: 7 May 2013
Document identifier: AN11119