MP1584
3A, 1.5MHz, 28V
Step-Down Converter
The Future of Analog IC Technology
MPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYDESCRIPTIONFEATURES

The MP1584 is a high frequency step-down
switching regulator with an integrated internal
high-side high voltage power MOSFET. It
provides 3A output with current mode control forfast loop response and easy compensation.

••

The wide 4.5V to 28V input range accommodates
a variety of step-down applications, including
those in an automotive input environment. A
100µA operational quiescent current allows use inbattery-powered applications.

•••High power conversion efficiency over a wide
load range is achieved by scaling down theswitching frequency at light load condition to
reduce the switching and gate driving losses.

APPLICATIONS

•

•
•
•
•
•
•

The frequency foldback helps prevent inductor
current runaway during startup and thermal
shutdown provides reliable, fault tolerant
operation.

Wide 4.5V to 28V Operating Input Range
Up to 1.5MHz Programmable Switching
Frequency
High-Efficiency Pulse Skipping Mode forLight Load
Ceramic Capacitor Stable
Internal Soft-Start
Internally Set Current Limit without aCurrent Sensing Resistor
Available in SOIC8E Package.
High Voltage Power Conversion
Automotive Systems
Industrial Power Systems
Distributed Power Systems
Battery Powered Systems“MPS” and “The Future of Analog IC Technology” are Registered Trademarks ofMonolithic Power Systems, Inc.

By switching at 1.5MHz, the MP1584 is able toprevent EMI (Electromagnetic Interference) noiseproblems, such as those found in AM radio and
ADSL applications.
The MP1584 is available in a thermally enhanced
SOIC8E package.

TYPICAL APPLICATION
Efficiency Curve
C4
100nF

1

(fSW=500kHz)

0.9
10
8,9

VIN

BST

SW

1,2

VOUT
3.3V
D1

EN

3

7

EN

MP1584

FB

COMP

FREQ

5

4

0.8
EFFICIENCY (%)

VIN

VIN=12V

0.7
0.6

VIN=24V

0.5
0.4
0.3

GND

0.2

6

0.1
0
0.01

0.1

1

10

OUTPUT CURRENT (A)MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

ORDERING INFORMATIONPart Number*

Package

Top Marking

Temperature

MP1584EN

SOIC8E

MP1584EN–20°C to +85°C* For Tape & Reel, add suffix –Z (e.g. MP1584EN–Z); For RoHS Compliant Packaging, add suffix –LF. (e.g.
MP1584EN–LF–Z)

PACKAGE REFERENCETOP VIEW
SW

1

8

BST

EN

2

7

VIN

COMP

3

6

FREQ

FB

4

5

GND

ABSOLUTE MAXIMUM RATINGS (1)Supply Voltage (VIN).....................–0.3V to +30V
Switch Voltage (VSW)............ –0.3V to VIN + 0.3V
BST to SW .....................................–0.3V to +6V
All Other Pins .................................–0.3V to +6V
Continuous Power Dissipation(TA = +25°C)(2)............................................................. 2.5W
Junction Temperature ...............................150°C
Lead Temperature ....................................260°C
Storage Temperature.............. –65°C to +150°C

MP1584 Rev. 1.0
4/7/2009

Recommended Operating Conditions(3)

Supply Voltage VIN ........................... 4.5V to 28V
Output Voltage VOUT ........................ 0.8V to 30V
Operating Temperature .............–20°C to +85°C

Thermal Resistance

(4)

θJA

θJC

SOIC8E .................................. 50 ...... 10... °C/W
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/ θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7, 4-layer PCB.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

ELECTRICAL CHARACTERISTICS
VIN = 12V, VEN = 2.5V, VCOMP = 1.4V, TA= +25°C, unless otherwise noted.
Parameter

Symbol Condition

Feedback Voltage
Upper Switch On ResistanceUpper Switch Leakage
Current Limit
COMP to Current Sense
Transconductance
Error Amp Voltage Gain (5)Error Amp Transconductance
Error Amp Min Source current
Error Amp Min Sink current
VIN UVLO Threshold
VIN UVLO Hysteresis
Soft-Start Time (5)VFB
RDS(ON)

4.5V < VIN < 28V
VBST – VSW = 5V
VEN = 0V, VSW = 0V, VIN = 28V

Min

Typ

Max

Units

0.776

0.8
150
1
4.7

0.824

V
mΩ
μA
A

4.0
GCS

9
ICOMP = ±3µA
VFB = 0.7V
VFB = 0.9V

40

2.7
0V < VFB < 0.8V

200
60
5
–5
3.0
0.35
1.5

Oscillator Frequency

RFREQ = 100kΩ

1

Shutdown Supply Current
Quiescent Supply Current

VEN = 0V
No load, VFB = 0.9V

12100

Thermal Shutdown
Thermal Shutdown Hysteresis(5)

Minimum Off Time
Minimum On Time (5)EN Up Threshold
EN Hysteresis

1.35

A/V
80

3.3

V/V
µA/V
µA
µA
V
V
ms
MHz

20
125

µA
µA

150

°C

15

°C
ns
ns
V
mV

100
100
1.5
300

1.65

Note:
5) Guaranteed by design.

MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYPIN FUNCTIONS
SOIC
Pin #

Name

1

SW

2

EN

3

COMP

4

FB

5
6
7
8

Description
Switch Node. This is the output from the high-side switch. A low forward drop Schottky diode to
ground is required. The diode must be close to the SW pins to reduce switching spikes.
Enable Input. Pulling this pin below the specified threshold shuts the chip down. Pulling it up
above the specified threshold or leaving it floating enables the chip.
Compensation. This node is the output of the error amplifier. Control loop frequency
compensation is applied to this pin.
Feedback. This is the input to the error amplifier. The output voltage is set by a resistive divider
connected between the output and GND which scales down VOUT equal to the internal +0.8V
reference.

GND
Ground. It should be connected as close as possible to the output capacitor to shorten the highExposedcurrent switch paths. Connect exposed pad to GND plane for optimal thermal performance.
Pad
Switching Frequency Program Input. Connect a resistor from this pin to ground to set theFREQ
switching frequency.
Input Supply. This supplies power to all the internal control circuitry, both BS regulators and theVINhigh-side switch. A decoupling capacitor to ground must be placed close to this pin to minimize
switching spikes.
Bootstrap. This is the positive power supply for the internal floating high-side MOSFET driver.
BST
Connect a bypass capacitor between this pin and SW pin.

MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, VOUT=5V, C1 = 10µF, C2 = 22µF, L1= 10µH, TA = +25°C, unless otherwise noted.
Oscillating Frequency
vs Rfreq
1500
1250
1000
750
500
250
0

10

100

1000

Steady State

Steady State

Steady StateIOUT=0.1A, fSW=500kHz

IOUT=1A, fSW=500kHz

IOUT=2A, fSW=500kHzVOUT
AC Coupled
10mV/div.

VOUT
AC Coupled
10mV/div.

VOUT
AC Coupled
10mV/div.

VSW
10V/div.

VSW
10V/div.

VSW
10V/div.

IL
1A/div.

IL
2A/div.

IL
1A/div.

1

MP1584 Rev. 1.0
4/7/2009

v.

2

v.

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2

v.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 12V, C1 = 10µF, C2 = 22µF, L1 = 10µH, fSW=500KHz, and TA = +25°C, unless otherwise noted.
StartupShutdown

Startup

IOUT = 0.1A

IOUT = 0.1A

IOUT = 1A

VEN
5V/div.

VEN
5V/div.

VEN
5V/div.

VOUT
2V/div.
VSW
10V/div.

VOUT
2V/div.

VOUT
2V/div.

VSW
10V/div.

VSW
10V/div.

IL
1A/div.

IL
1A/div.

IL
1A/div.

5ms/div.

1ms/div.

Shutdown

Startup

IOUT = 1A

IOUT = 2A

5ms/div.

Shutdown
IOUT = 2A

VEN
5V/div.

VEN
5V/div.

VEN
5V/div.

VOUT
2V/div.

VOUT
2V/div.

VOUT
2V/div.

VSW
10V/div.

VSW
10V/div.

VSW
10V/div.

IL
1A/div.

IL
2A/div.

IL
2A/div.

5ms/div.

Short Circuit Entry

Short Circuit Recovery

IOUT = 0.1A to Short

IOUT = Short to 0.1A

VOUT
2V/div.

VOUT
2V/div.

IL
1A/div.

IL
1A/div.

MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYBLOCK DIAGRAM
VIN

VIN

EN

REFERENCE UVLO/THERMAL
SHUTDOWN

5V +
-2.6V

INTERNAL
REGULATORS

+
-BST

SW
1.5ms SS

VOUT

SS

--

ISW

+
ISW

Level
Shift

FB

SW

Gm Error Amp
SS
0V8

--

COMP

+

OSCILLATOR

CLK
VOUT

COMP

GND

FREQ

Figure 1—Functional Block Diagram

OPERATION
The MP1584 is a variable frequency,
non-synchronous,
step-down
switchingregulator with an integrated high-side highvoltage power MOSFET. It provides a highly
efficient solution with current mode control forfast loop response and easy compensation. Itfeatures a wide input voltage range, internal
soft-start control and precision current limiting.
Its very low operational quiescent current
makes it suitable for battery powered
applications.

MP1584 Rev. 1.0
4/7/2009

PWM Control
At moderate to high output current, the MP1584
operates in a fixed frequency, peak current
control mode to regulate the output voltage. A
PWM cycle is initiated by the internal clock. The
power MOSFET is turned on and remains on
until its current reaches the value set by the
COMP voltage. When the power switch is off, itremains off for at least 100ns before the next
cycle starts. If, in one PWM period, the current
in the power MOSFET does not reach the
COMP set current value, the power MOSFET
remains on, saving a turn-off operation.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY
Error Amplifier
The error amplifier compares the FB pin voltage
with the internal reference (REF) and outputs acurrent proportional to the difference between
the two. This output current is then used tocharge the external compensation network toform the COMP voltage, which is used tocontrol the power MOSFET current.
During operation, the minimum COMP voltage
is clamped to 0.9V and its maximum is clamped
to 2.0V. COMP is internally pulled down to GND
in shutdown mode. COMP should not be pulled
up beyond 2.6V.
Internal Regulator
Most of the internal circuitries are powered fromthe 2.6V internal regulator. This regulator takes
the VIN input and operates in the full VIN range.
When VIN is greater than 3.0V, the output of
the regulator is in full regulation. When VIN islower than 3.0V, the output decreases.
Enable Control
The MP1584 has a dedicated enable control pin(EN). With high enough input voltage, the chipcan be enabled and disabled by EN which has
positive logic. Its falling threshold is a precision
1.2V, and its rising threshold is 1.5V (300mV
higher).
When floating, EN is pulled up to about 3.0V by
an internal 1µA current source so it is enabled.
To pull it down, 1µA current capability is needed.
When EN is pulled down below 1.2V, the chip is
put into the lowest shutdown current mode.
When EN is higher than zero but lower than its
rising threshold, the chip is still in shutdown
mode but the shutdown current increases
slightly.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The UVLO rising threshold isabout 3.0V while its falling threshold is aconsistent 2.6V.

MP1584 Rev. 1.0
4/7/2009

Internal Soft-Start
The soft-start is implemented to prevent theconverter output voltage from overshooting
during startup. When the chip starts, theinternal circuitry generates a soft-start voltage(SS) ramping up from 0V to 2.6V. When it islower than the internal reference (REF), SS
overrides REF so the error amplifier uses SS as
the reference. When SS is higher than REF,
REF regains control.
Thermal Shutdown
Thermal shutdown is implemented to preventthe chip from operating at exceedingly hightemperatures. When the silicon die temperature
is higher than its upper threshold, it shuts down
the whole chip. When the temperature is lower
than its lower threshold, the chip is enabledagain.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is poweredby an external bootstrap capacitor. This floating
driver has its own UVLO protection. ThisUVLO’s rising threshold is 2.2V with a thresholdof 150mV.
The bootstrap capacitor is charged andregulated to about 5V by the dedicated internalbootstrap regulator. When the voltage between
the BST and SW nodes is lower than its
regulation, a PMOS pass transistor connectedfrom VIN to BST is turned on. The charging
current path is from VIN, BST and then to SW.
External circuit should provide enough voltage
headroom to facilitate the charging.
As long as VIN is sufficiently higher than SW,
the bootstrap capacitor can be charged. Whenthe power MOSFET is ON, VIN is about equal
to SW so the bootstrap capacitor cannot becharged. When the external diode is on, thedifference between VIN and SW is largest, thus
making it the best period to charge. When there
is no current in the inductor, SW equals theoutput voltage VOUT so the difference between
VIN and VOUT can be used to charge thebootstrap capacitor.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY
At higher duty cycle operation condition, thetime period available to the bootstrap charging
is less so the bootstrap capacitor may not be
sufficiently charged.
In case the internal circuit does not havesufficient voltage and the bootstrap capacitor is
not charged, extra external circuitry can beused to ensure the bootstrap voltage is in thenormal operational region. Refer to External
Bootstrap Diode in Application section.
The DC quiescent current of the floating driveris about 20µA. Make sure the bleeding current
at the SW node is higher than this value, such
that:
IO +

VO
> 20μA(R1 + R2)

Current Comparator and Current Limit
The power MOSFET current is accurately
sensed via a current sense MOSFET. It is thenfed to the high speed current comparator for thecurrent mode control purpose. The current
comparator takes this sensed current as one of
its inputs. When the power MOSFET is turned
on, the comparator is first blanked till the end of
the turn-on transition to avoid noise issues. The
comparator then compares the power switch
current with the COMP voltage. When thesensed current is higher than the COMP
voltage, the comparator output is low, turning
off the power MOSFET. The cycle-by-cycle
maximum current of the internal power
MOSFET is internally limited.

MP1584 Rev. 1.0
4/7/2009

Startup and Shutdown
If both VIN and EN are higher than theirappropriate thresholds, the chip starts. The
reference block starts first, generating stablereference voltage and currents, and then theinternal regulator is enabled. The regulator
provides stable supply for the remaining
circuitries.
While the internal supply rail is up, an internal
timer holds the power MOSFET OFF for about
50µs to blank the startup glitches. When theinternal soft-start block is enabled, it first holds
its SS output low to ensure the remaining
circuitries are ready and then slowly ramps up.
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, power MOSFET is turned off first to
avoid any fault triggering. The COMP voltage
and the internal supply rail are then pulled down.
Programmable Oscillator
The MP1584 oscillating frequency is set by an
external resistor, Rfreq from the FREQ pin toground. The value of Rfreq can be calculatedfrom:
180000R freq (KΩ) =fs (KHz)1.1

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYAPPLICATION INFORMATIONCOMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB pin.
The voltage divider divides the output voltage
down to the feedback voltage by theratio:VFB = VOUT

R2
R1 + R2

Thus the output voltage is:(R1 + R2)
VOUT = VFB
R2

About 20µA current from high side BS circuitry
can be seen at the output when the MP1584 is
at no load. In order to absorb this small amountof current, keep R2 under 40KΩ. A typicalvalue for R2 can be 40.2kΩ. With this value, R1
can be determined by:
R1 = 50.25 × ( VOUT − 0.8)(kΩ)

For example, for a 3.3V output voltage, R2 is
40.2kΩ, and R1 is 127kΩ.
Inductor
The inductor is required to supply constantcurrent to the output load while being driven by
the switched input voltage. A larger value
inductor will result in less ripple current that will
result in lower output ripple voltage. However,the larger value inductor will have a larger
physical size, higher series resistance, and/or
lower saturation current.

MP1584 Rev. 1.0
4/7/2009

A good rule for determining the inductance to
use is to allow the peak-to-peak ripple current in
the inductor to be approximately 30% of the
maximum switch current limit. Also, make surethat the peak inductor current is below the
maximum switch current limit. The inductancevalue can be calculated by:
L1 =

⎛
⎞
VOUT
V
× ⎜1 − OUT ⎟⎟fS × ΔIL ⎜⎝VIN ⎠Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ΔIL is
the peak-to-peak inductor ripple current.
Choose an inductor that will not saturate underthe maximum inductor peak current. The peak
inductor current can be calculated by:
ILP = ILOAD +

⎛
⎞
VOUT
V
× ⎜⎜1 − OUT ⎟⎟2 × fS × L1 ⎝VIN ⎠Where ILOAD is the load current.
Table 1 lists a number of suitable inductors
from various manufacturers. The choice of
which style inductor to use mainly depends on
the price vs. size requirements and any EMI
requirement.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY
Table 1—Inductor Selection Guide
Inductance (µH)

Max DCR (Ω)

Current Rating (A)Dimensions
L x W x H (mm3)7447789003

3.3

0.024

3.42

7.3x7.3x3.2

744066100

10

0.035

3.6

10x10x3.8744771115

15

0.025

3.75

12x12x6

744771122

22

0.031

3.37

12x12x6

RLF7030T-3R3

3.3

0.02

4.1

7.3x6.8x3.2

RLF7030T-4R7

4.7

0.031

3.4

7.3x6.8x3.2

SLF10145T-100

100.03643

10.1x10.1x4.5

SLF12565T-220M3R5

22

0.03163.5

12.5x12.5x6.5

FDV0630-3R3M

3.3

0.031

4.3

7.7x7x3

FDV0630-4R7M

4.7

0.049

3.3

7.7x7x3

919AS-100M

100.02654.3

10.3x10.3x4.5

919AS-160M

16

0.0492

3.3

10.3x10.3x4.5

919AS-220M

22

0.07763

10.3x10.3x4.5

Part Number
Wurth Electronics

TDK

Toko

Output Rectifier DiodeThe output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.

Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating isgreater than the maximum load current. Table 2
lists
exampleSchottkydiodesandmanufacturers.

Input Capacitor
The input current to the step-down converter isdiscontinuous, therefore a capacitor is required tosupply the AC current to the step-down converter
while maintaining the DC input voltage. Use low
ESR capacitors for the best performance. Ceramic
capacitors are preferred, but tantalum or low-ESR
electrolytic capacitors may also suffice.

For simplification, choose the input capacitor
with RMS current rating greater than half of the
maximum load current.

Table 2—Diode Selection Guide
Diodes
B340A-13-F
CMSH3-40MA

MP1584 Rev. 1.0
4/7/2009

Voltage/
Current
Rating
40V, 3A
40V, 3A

Manufacturer
Diodes Inc.
Central Semi

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

The input capacitor (C1) can be electrolytic,
tantalum or ceramic. When using electrolytic ortantalum capacitors, a small, high quality
ceramic capacitor, i.e. 0.1μF, should be placed
as close to the IC as possible. When using
ceramic capacitors, make sure that they haveenough capacitance to provide sufficient charge
to prevent excessive voltage ripple at input. The
input voltage ripple caused by capacitance canbe estimated by:
ΔVIN =

⎛
⎞
ILOAD
V
V
× OUT × ⎜1 − OUT ⎟⎟fS × C1 VIN ⎜⎝VIN ⎠Output Capacitor
The output capacitor (C2) is required tomaintain the DC output voltage. Ceramic,
tantalum, or low ESR electrolytic capacitors arerecommended. Low ESR capacitors are
preferred to keep the output voltage ripple low.
The output voltage ripple can be estimated by:
ΔVOUT =⎞
⎞ ⎛VOUT ⎛
V1⎟
× ⎜⎜1 − OUT ⎟⎟ × ⎜⎜ R ESR +fS × L ⎝VIN ⎠ ⎝
8 × f S × C2 ⎟⎠Where L is the inductor value and RESR is theequivalent series resistance (ESR) value of theoutput capacitor.
In the case of ceramic capacitors, theimpedance at the switching frequency isdominated by the capacitance. The output
voltage ripple is mainly caused by thecapacitance. For simplification, the output
voltage ripple can be estimated by:
ΔVOUT =⎛⎞
V× ⎜⎜1 − OUT ⎟⎟VIN ⎠8 × fS × L × C2 ⎝VOUT
2In the case of tantalum or electrolytic capacitors,
the ESR dominates the impedance at theswitching frequency. For simplification, theoutput ripple can be approximated to:
ΔVOUT =

VOUT ⎛
V⎞× ⎜1 − OUT ⎟⎟ × R ESR
f S × L ⎜⎝VIN ⎠The characteristics of the output capacitor also
affect the stability of the regulation system. The
MP1584 can be optimized for a wide range ofcapacitance and ESR values.

MP1584 Rev. 1.0
4/7/2009

Compensation Components
MP1584 employs current mode control for easycompensation and fast transient response. The
system stability and transient response arecontrolled through the COMP pin. COMP pin is
the output of the internal error amplifier. A
series capacitor-resistor combination sets apole-zerocombination
tocontrolthecharacteristics of the control system. The DC
gain of the voltage feedback loop is given by:
A VDC = R LOAD × G CS × A VEA ×

VFB
VOUT

Where AVEA is the error amplifier voltage gain,
200V/V;GCS
isthecurrent
sense
transconductance, 9A/V; RLOAD is the load
resistor value.
The system has two poles of importance. One
is due to the compensation capacitor (C3), theoutput resistor of error amplifier. The other isdue to the output capacitor and the load resistor.
These poles are located at:
fP1 =

GEA
2π × C3 × A VEA

fP2 =

1
2π × C2 × R LOAD

isthe
Where,
GEA
transconductance, 60μA/V.

error

amplifierThe system has one zero of importance, due tothe compensation capacitor (C3) and thecompensation resistor (R3). This zero is locatedat:f Z1 =

1
2π × C3 × R3

The system may have another zero ofimportance, if the output capacitor has a large
capacitance and/or a high ESR value. The zero,due to the ESR and capacitance of the output
capacitor, is located at:
fESR =

1
2π × C2 × R ESR

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

In this case (as shown in Figure 2), a third pole
set by the compensation capacitor (C6) and thecompensation resistor (R3) is used tocompensate the effect of the ESR zero on theloop gain. This pole is located at:
f P3 =

1
2π × C6 × R3

1. Choose the compensation resistor (R3) to set
the desired crossover frequency. Determine theR3 value by the following equation:
R3 =2π × C2 × f C VOUT×G EA × G CS
VFB

Where fC is the desired crossover frequency.

The goal of compensation design is to shape
the converter transfer function to get a desired
loop gain. The system crossover frequency
where the feedback loop has the unity gain is
important. Lower crossover frequencies resultin slower line and load transient responses,
while higher crossover frequencies could cause
system unstable. A good rule of thumb is to set
the crossover frequency to approximately onetenth of the switching frequency. The Table 3
lists the typical values of compensation
components for some standard output voltages
with various output capacitors and inductors.
The values of the compensation components
have been optimized for fast transient
responses and good stability at given conditions.
Table 3—Compensation Values for Typical
Output Voltage/Capacitor Combinations
VOUT
(V)

L (µH)

C2
(µF)

R3
(kΩ)

C3
(pF)

C6

1.8

4.7

47

105

100

None

2.5

4.7 - 6.8

22

54.9

220

None

3.3

6.8 -10

22

68.1

220

None

5

15 - 22

22

100

150

None

12

22 - 33

22

147

150

None

2. Choose the compensation capacitor (C3) toachieve the desired phase margin. For
applications with typical inductor values, setting
the compensation zero, fZ1, below one forth ofthe crossover frequency provides sufficientphase margin. Determine the C3 value by thefollowing equation:
C3 >4
2π × R3 × f C

3. Determine if the second compensation
capacitor (C6) is required. It is required if the
ESR zero of the output capacitor is located atless than half of the switching frequency, or thefollowing relationship is valid:f1< S
2π × C2 × R ESR
2

If this is the case, then add the secondcompensation capacitor (C6) to set the pole fP3
at the location of the ESR zero. Determine theC6 value by the equation:
C6 =C2 × R ESR
R3

To optimize the compensation components forconditions not listed in Table 3, the following
procedure can be used.

MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYHigh Frequency Operation
The switching frequency of MP1584 can be
programmed up to 1.5MHz with an external
resistor.

With higher switching frequencies, the inductive
reactance (XL) of capacitor comes to dominate,
so that the ESL of input/output capacitor
determines the input/output ripple voltage at
higher switching frequency. As a result of that,high frequency ceramic capacitor is strongly
recommended as input decoupling capacitor
and output filtering capacitor for such highfrequency operation.
Layout becomes more important when thedevice switches at higher frequency. It isessential to place the input decoupling
capacitor, catch diode and the MP1584 (Vin pin,
SW pin and PGND) as close as possible, withtraces that are very short and fairly wide. Thiscan help to greatly reduce the voltage spike on
SW node, and lower the EMI noise level as well.
Try to run the feedback trace as far from theinductor and noisy power traces as possible. It
is often a good idea to run the feedback traceon the side of the PCB opposite of the inductor
with a ground plane separating the two. The
compensation components should be placed
closed to the MP1584. Do not place thecompensation components close to or underhigh dv/dt SW node, or inside the high di/dt
power loop. If you have to do so, the proper
ground plane must be in place to isolate those.
Switching loss is expected to be increased athigh switching frequency. To help to improve
the thermal conduction, a grid of thermal vias
can be created right under the exposed pad. It
is recommended that they be small (15mil
barrel diameter) so that the hole is essentiallyfilled up during the plating process, thus aiding
conduction to the other side. Too large a holecan cause ‘solder wicking’ problems during thereflow soldering process. The pitch (distance
between the centers) of several such thermal
vias in an area is typically 40mil.

MP1584 Rev. 1.0
4/7/2009

External Bootstrap Diode
It is recommended that an external bootstrap
diode be added when the input voltage is no
greater than 5V or the 5V rail is available in thesystem. This helps improve the efficiency of theregulator. The bootstrap diode can be a low
cost one such as IN4148 or BAT54.
5V

BSMP1584SW

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty
cycle operation (when VOUT /VIN >65%) or low
VIN (<5Vin) applications.
At no load or light load, the converter may
operate in pulse skipping mode in order tomaintain the output voltage in regulation. Thus
there is less time to refresh the BS voltage. In
order to have enough gate voltage under suchoperating conditions, the difference of VIN –VOUT
should be greater than 3V. For example, if the
VOUT is set to 3.3V, the VIN needs to be higher
than 3.3V+3V=6.3V to maintain enough BS
voltage at no load or light load. To meet thisrequirement, EN pin can be used to program
the input UVLO voltage to Vout+3V.

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY

TYPICAL APPLICATION CIRCUITS
C4
100nF
8
7

VIN
4.5V - 28V

BST

VIN

1

SW

VOUT
1.8V
D1

2

EN

6

EN

MP1584

4

FB

3

COMP

FREQ

C3
100pF

GND
5

C6
NS

Figure 3—1.8V Output Typical Application Schematic
C4
100nF
8
VIN
8V - 28V

7

VIN

BST

SW

1

VOUT
5V
D1

EN

2

6

EN

MP1584

FB

COMP

FREQ
GND
5

4

3
C3
150pF

C6
NS

Figure 4—5V Output Typical Application Schematic

MP1584 Rev. 1.0
4/7/2009

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MP1584 – 3A, 1.5MHz, 28V STEP-DOWN CONVERTERMPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLYPACKAGE INFORMATIONSOIC8E (EXPOSED PAD)
0.189(4.80)
0.197(5.00)

0.124(3.15)
0.136(3.45)

850.150(3.80)
0.157(4.00)

PIN 1 ID1

0.228(5.80)
0.244(6.20)

0.089(2.26)
0.101(2.56)

4

TOP VIEW

BOTTOM VIEW

SEE DETAIL "A"
0.051(1.30)
0.067(1.70)
SEATING PLANE
0.000(0.00)
0.006(0.15)

0.013(0.33)
0.020(0.51)

0.0075(0.19)
0.0098(0.25)

SIDE VIEW

0.050(1.27)
BSC

FRONT VIEW

0.010(0.25)
x 45o
0.020(0.50)
GAUGE PLANE
0.010(0.25) BSC

0.050(1.27)

0.024(0.61)

0o-8o

0.016(0.41)
0.050(1.27)

0.063(1.60)

DETAIL "A"
0.103(2.62)

0.138(3.51)

RECOMMENDED LAND PATTERN

0.213(5.40)

NOTE:1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASHOR PROTRUSIONS.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA.
6) DRAWING IS NOT TO SCALE.

NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third
party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will notassume any legal responsibility for any said applications.
MP1584 Rev. 0.9
4/7/2009

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