Light Load High Efficiency
Synchronous Rectification Buck Converter IC

NR263S

Data Sheet

Description

Package

The NR263S is synchronous rectification buckconverter IC with built-in power MOSFET. In light load,
the IC operates with the pulse skip mode to improve theefficiency. By using the peak current control method, theIC stably operates with a low ESR capacitor such as aceramic capacitor. The IC has the various protections
such as the overcurrent protection, the undervoltage
lockout, and the thermal shutdown.
The IC achieves the switching regulator circuit withfew components and small mounting area.

SOP8

Features

Specifications● Synchronous Rectification● Operation Modes:
Normal Load: Current Mode PWM Control
Light Load: Pulse Skip Operation● Maximum Efficiency (VIN = 9 V, VOUT = 5 V)
Normal Load: 93%
Light Load (IOUT = 10 mA): 86%● Stable with a Low ESR Ceramic Output Capacitor● Few External Component Counts(Fixed Output Voltage of 5 V)
● Soft-start Period Adjustment by External Capacitor● Enable Function● Protections:Overcurrent Protection (OCP): Drooping Type, Autorestart
Thermal Shutdown (TSD): Auto-restart
Undervoltage Lockout (UVLO)
Output Short Circuit Protection: Burst Oscillation
Operation (Hiccup)● Input Voltage, VIN: 8.0 V to 31 V
● Fixed Output Voltage, VOUT: 5 V● Output Current, IOUT: 1 A● Fixed Operating Frequency: 500 kHz

Not to scale

Applications● White Goods● Audio Visual Equipment● Office Automation Equipment● Other Switched Mode Power Supply (SMPS)

Typical Application
VIN

REN
6

5

IN

EN

NC

7

VO

8

CSS

BS
2

SW

SS
1

GND

NR263S

CIN

3

CBS

4

L

VOUT
COUT

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NR263S
Contents
Description ------------------------------------------------------------------------------------------------------ 1
Contents --------------------------------------------------------------------------------------------------------- 2
1. Absolute Maximum Ratings----------------------------------------------------------------------------- 3
2. Recommended Operating Conditions ----------------------------------------------------------------- 3
3. Electrical Characteristics -------------------------------------------------------------------------------- 4
4. Block Diagram --------------------------------------------------------------------------------------------- 5
5. Pin Configuration Definitions --------------------------------------------------------------------------- 5
6. Typical Application --------------------------------------------------------------------------------------- 6
7. Physical Dimensions -------------------------------------------------------------------------------------- 7
8. Marking Diagram ----------------------------------------------------------------------------------------- 8
9. Operational Descriptions -------------------------------------------------------------------------------- 8
9.1 PWM Output Control ------------------------------------------------------------------------------ 9
9.2 Enable Function ------------------------------------------------------------------------------------- 9
9.3 Soft-start Function ---------------------------------------------------------------------------------- 9
9.4 Thermal Shutdown -------------------------------------------------------------------------------- 10
9.5 Overcurrent Protection and Output Short Circuit Protection --------------------------- 11
9.6 Pulse Skip Mode ----------------------------------------------------------------------------------- 12
10. Design Notes ---------------------------------------------------------------------------------------------- 13
10.1 Thermal Derating --------------------------------------------------------------------------------- 13
10.2 External Components ---------------------------------------------------------------------------- 13
10.2.1 Inductor --------------------------------------------------------------------------------------- 13
10.2.2 Input/Output Capacitor -------------------------------------------------------------------- 14
10.3 Spike Noise Reduction Methods ---------------------------------------------------------------- 15
10.4 For Applications Where Output Voltage Is Higher than Input Voltage --------------- 15
10.5 For Applications Inserting/Removing Load Wire in Power Supply Operation ------- 15
10.6 PCB Layout----------------------------------------------------------------------------------------- 16
10.7 Using Bead-core ----------------------------------------------------------------------------------- 16
11. Pattern Layout Example ------------------------------------------------------------------------------- 17
12. Typical Characteristics --------------------------------------------------------------------------------- 19
Important Notes ---------------------------------------------------------------------------------------------- 21

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NR263S
1.

Absolute Maximum Ratings

Current polarities are defined as follows: current going into the IC (sinking) is positive current (+); current coming outof the IC (sourcing) is negative current (−).
Unless otherwise specified, TA = 25 °C.
Parameter
SymbolConditions
Ratings
Unit
Input Voltage

VIN−0.3 to 35

V

BS Pin Voltage

VBS−0.3 to 40.5

V

Voltage between BS and
SW Pins−0.3 to 5.5

VBS-SW

V

8

V

SW Pin Voltage

VSW

DC
Pulse width ≤10 ns
DC−1 to 35

Pulse width ≤100 ns−2 to 35

Pulse width ≤10 ns−6 to 35

V

VO Pin Voltage

VO−0.3 to 6

V

EN Pin Voltage

VEN−0.3 to 35

V

SS Pin Voltage

VSS−0.3 to 7.0

V

SS Pin Sink Current

ISSB

5.0

mA

1.56

W

−40 to 150°C−40 to 150

°C

60

°C/W

80

°C/W

Power Dissipation(1)PD

Junction Temperature(2)

TJ

Mounted on the board (seeSection 0),
TJ = 150 °C

Storage Temperature
TsSTG
(3)
Junction-to-Lead
θJ-L
Thermal ResistanceJunction-to-Ambient
Mounted on the board
θJ-A
Thermal Resistance(see Section 0)(1)
Limited by thermal shutdown.
(2)
The temperature detection of thermal shutdown is about 165 °C.
(3)The lead temperature is measured at pin 4.

2.

Recommended Operating Conditions
Parameter

SymbolInput Voltage

VIN

Output Current*

IOUT

Operating Ambient Temperature*TA

Conditions
L = 6.8 μH

Operating Junction Temperature*
TJ* Must be used in the range of thermal derating (see Section 10.1).

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Min.

Max.

Unit

8

31

V

0

1.0

A

−40

85

°C

−40

125

°C

3

NR263S
3.

Electrical Characteristics

Current polarities are defined as follows: current going into the IC (sinking) is positive current (+); current coming outof the IC (sourcing) is negative current (−).
Unless otherwise specified, TA = 25 °C.
Parameter
SymbolConditions
Min
Typ.
Max
Unit
Output Voltage
Output Voltage Temperature
Coefficient
Operating Frequency

VOUT
ΔVOUT/ΔT
fO

4.85

5.00

5.15

V

—

±0.3

—

mV/°C

−30%

500

30%

kHz

—

50

—

mV

—

50

—

mV

VIN = 12 V, VOUT = 5.0 V

−2.6

−1.5

−1.1

A

—

250

—

μA

—

1.2

10

μA

VIN = 12 V, IOUT = 0.5 A
VIN = 12 V, IOUT = 0.5 A,−40 °C to 85 °C
VIN = 12 V, VOUT = 5.0
V,
IOUT = 0.5 A
VIN = 8 V to 31 V,
VOUT = 5.0 V,
IOUT = 0.5 A
VIN = 12 V, VOUT = 5.0 V
IOUT = 0.1 A to 1.0 A

Line Regulation*

VLINE

Load Regulation*

VLOAD

Overcurrent Protection
Start Current

IS

Operating Circuit Current

IIN

Quiescent Circuit Current

IIN(OFF)

VIN = 12 V, VEN = 12 V,
IO = 0 mA
VIN = 12 V,VEN = 0 V

UVLO Threshold Voltage

VUVLO

VIN increases

5

6

7

V

UVLO Hysteresis Voltage

VUVLO_HYSUVLO on to UVLO off

—

0.55

—

V

SS Pin Capacitor Charge Current

ISS

VSS = 0 V, VIN = 12 V

−8.5

−5.0

−2.5

μA

EN Pin Sink Current

IEN

VEN = 12 V, VIN = 12 V

—

14

30

μA

EN Pin On Threshold Voltage

VEN

VIN =12 V

0.8

1.1

2.1

V

EN Pin Hysteresis Voltage

VEN_HYS

VIN =12 V

—

0.15

—

V

Maximum Duty Cycle*

DMAX

VIN = 12 V

—

85

—

%

Minimum On-time*
Thermal Shutdown Operation
Temperature *Thermal Shutdown Restart
Hysteresis*
High-side Power MOSFET Onresistance*
Low-side Power MOSFET Onresistance** Guaranteed by design.

tON(MIN)

VIN = 12 V

—

200

—

ns

TSD

VIN = 12 V

151

165

—

°C

TSD_HYS

VIN = 12 V

—

15

—

°C

RONH

VIN = 12 V

—

250

—

mΩ

RONL

VIN = 12 V

—

200

—

mΩ

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NR263S
4.

Block Diagram
5

2
6

3

4

7

1

8

5.

Pin Configuration Definitions
SS 1

8 NC

BS 2

7 VO

SW 3

6 EN

GND 4

5

IN

Pin
Number

Pin
Name

1

SS

2

BS

3

SW

4

GND

5

IN

6

EN

7

VO

8

NC

Description
Soft-start period setting pin. Capacitor for soft-start
period setting is connected between the SS and GND
pins.
Power supply pin for the high-side MOSFET drive
circuit. Connect a capacitor between the SW and BS
pins.
Output pin. The LC filter for the output is connectedto the SW pin.
GroundPower supply input pin of the IC
Enable signal input pin. When the EN pin input ishigh level, the regulator is enabled. When it is low
level, the regulator is disabled.
Feedback pin, which compares the reference voltage(5 V) with output voltage. The VO pin is directly
connected to the output voltage.
No connection

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5

NR263S
6.

Typical Application
VIN

REN
5

IN

EN

6

VO

7
NC

8

CSS

BS
2

SW

SS

1

GND

NR263S

CIN

3

4

L

VOUT

CBS

Figure 6-1.

COUT

Typical Application

Table 6-1. Reference Value (VIN = 12 V)
SymbolReference ValueCIN

10 μF, 25 V

COUT

22 μF, 16 VCBS

0.1 μFCSS

0.1 μFL

6.8 μH*REN

100 kΩ

* Minimum value of inductor when the control duty cycle is set less than 0.5. When ΔIL is decreased, the required
inductance is increased.

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6

NR263S
7.

Physical Dimensions● SOP8 Package

NOTES:● Dimensions in millimeters● Bare lead frame: Pb-free (RoHS compliant)● SOP8 Land Pattern Example

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NR263S
8.

Marking Diagram
8
NR263SPart Number
SK YM WW

Lot Number:
Y is the last digit of the year of manufacture (0 to 9)
M is the month of the year (1 to 9, O, N, or D)
D is the period of days represented by:
1: the first 10 days of the month (1st to 10th)
2: the second 10 days of the month (11th to 20th)
3: the last 10–11 days of the month (21st to 31st)

1

Control Number

9.

Operational Descriptions

All the characteristic values given in this section are typical values, unless they are specified as minimum or maximum.
Current polarities are defined as follows: current going into the IC (sinking) is positive current (+); current coming out of
the IC (sourcing) is negative current (−).

5

2
6

3

4

7

8

Figure 9-1.

1

Basic Structure of Buck Regulator with PWM Control by Current Mode Control

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NR263S
9.1

Figure 9-2.

PWM Output Control

The PWM control circuit of the IC consists of thecurrent detection amplifier, the error amplifier, the PWM
comparator, and the slope superimposed circuit. The duty
cycle is controlled by comparing with VTRIP and VCOMP in
the PWM comparator. VTRIP is the drain current feedback
signal detected by the current detection amplifier. VCOMP
is the error amplification signal generated by the error
amplifier with the output voltage and the reference
voltage.
The slope superimposed circuit is for avoiding the subharmonic oscillation that is generated at the duty cycle of
50% or more. The slope signal is superimposed to the
feedback signal, VTRIP.
CBS in Figure 9-1 is the boost capacitor that is a power
supply for driving the high-side circuit in the IC and thehigh-side switch (M1). The power is supplied to the
output by the high-side MOSFET (M1) and the low-side
MOSFET (M2).
When the IN pin voltage becomes the UVLO
Threshold Voltage, VUVLO = 6 V, or more, and the EN pin
voltage increases threshold voltage or more, the SS pin
voltage increases. M2 is turned on to change CBS before
the SS pin voltage reaches 0.6 V. After that, when the SS
pin voltage increases 0.6 V or more, the IC starts theswitching operation. M1 and M2 repeat on and off
alternately. When M1 is turned on, the current of inductor,
L, is increased, and the output of current detection
amplifier is also increased. In the PWM comparator,
when VTRIP exceeds VCOMP, the IC turns off M1 and turns
on M2. The regenerative current of inductor flows via M2
from the GND pin. After that, M1 is turned on again when
receiving a set signal from the oscillator, OSC.

9.2

Enable Function

U1

VIN
CIN

5
REN

U1
VIN

5
REN

L

SW 3

IN

SW 3

IN

L

VOUT

6 EN

CIN

GND
4

COUT

Figure 9-3. EN Pin Peripheral Circuit(Not Using Enable Function)

9.3

Soft-start Function

Figure 9-4 and Figure 9-5 show the soft-start
operational waveform without the enable function andwith the enable function, respectively. The soft-start
period is set by the value of capacitor, CSS, connected
between the SS and GND pins. The output voltage, VOUT,
increases according to the SS pin voltage. CSS is charged
by the constant current supplied from the SS pin,
ISS = −5.0 μA. Thus, the SS pin voltage, VSS, increases
linearly. During the soft-start period, the IC controls theoutput rising period by controlling the off period of PWM
signal. The delay time, i.e., from enabling the IC tostarting the output voltage rising, is defined as tDELAY. The
soft-start period, tSS, of the output voltage is the range of
VSS = 0.6 V to 1.4 V.
The approximate values of tDELAY and tSS are calculatedby the following equations.
t DELAY =Figure 9-2 shows the EN pin peripheral circuit. The
signal is input to the EN pin using switching transistors.
When both of the following conditions are satisfied, theregulator is enabled and starts the switching operation: theIN pin voltage increases to UVLO Threshold Voltage,
VUVLO = 6 V, or more, and the EN pin voltage increases
to the On Threshold Voltage, VEN = 1.1 V, or more. Whenthe EN pin voltage decreases to VEN − VEN_HYS or less, theregulator is disabled, and stops the switching operationeven if the IN pin voltage is VUVLO or more. When notusing the enable function, the EN pin is pulled up to theIN pin as shown in Figure 9-3. The value of the pull-up
resistor, REN, is about 100 kΩ.

EN Pin Peripheral Circuit

t SS =

0.6 × CSS
|ISS |

0.8 × CSS
|ISS |(1)(2)

Where, ISS is charge current of the capacitor connectedto the SS pin (−5.0 μA).

VOUT

6 EN

GND
4

COUT

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NR263S
When the IC is restarted with the high SS pin voltage(e.g., input voltage variation, high-speed switching of the
EN pin signal), a forced discharge circuit in the IC
operates. Then, the SS pin voltage is decreased to 0.6 V
by the forced discharge circuit. After that, the soft-start
operation is started (see Figure 9-7). The value of internal
impedance at discharging is about 600 Ω.
When the IC is restarted with the high SS pin voltage,
VSS, the required period until the output voltage becomes
constant after the period on-signal is input to the EN pin
is tDIS + tSS. For applications that perform consecutive
on/off operation, this forced discharge period also must
be taken into account.
In steady operation, VSS, i.e., the voltage across CSS,
increases to the internal regulator voltage (1.8 V). Whendischarging CSS from 1.8 V, VSS in arbitrary time, t, iscalculated by Equation (3). The period until VSS decreases
to 0.6 V, tDIS, is calculated by Equation (4).

VIN
VUVLO
0

t

VSS

1.4 V
0.6 V

0

t

VOUT
0

tDELAYttSS

Figure 9-4. Soft-start Operational Waveform(Not Using Enable Function)
VIN
VUVLO
0

EN PinVoltaget−t × 600
VSS = 1.8 V × EXP (
)
CSS

(3)

t

0.6
t DIS = −CSS × 600 × ln ( )
1.8

(4)

VEN

0

VSS

1.4 V
0.6 V

0

t

VOUT
0

tDELAYEN PinVoltage
0

t

tSS

VEN
VEN−VEN_HYS
t

VSS
1.4 V

Figure 9-5. Soft-start Operational Waveform(Using Enable Function)

0.6 V

0

1.8 V

t

VOUT

Be sure to confirm the output rising waveform with theactual operation, and adjust the soft-start period. If tSS is
too short, the soft-start period ends before the constantvoltage control follows, and the output voltage may
overshoot excessively (see Figure 9-6). If tSS is long, theovershoot is reduced, but the startup period becomes long.
VSS
0

1.4 V
0.6 V
t

VOUT
0

t

Figure 9-6. Soft-start Operational Waveform(Soft-start Period is Too Short)0

Figure 9-7.

9.4

tDIS

tSS

t

CSS Forced Discharge and Soft-start
Operational Waveform(Using Enable Function)

Thermal Shutdown

When the junction temperature of the IC increases to
the Thermal Shutdown Operation Temperature,
TSD = 165 °C, or more, the thermal shutdown (TSD)
operates, and the IC stops the oscillation. TSD has the
Thermal Shutdown Restart Hysteresis, TSD_HYS = 15 °C.
When the IC temperature decreases to TSD − TSD_HYS or
less, the IC returns the normal operation automatically.
The purpose of TSD is to protect the IC when the lossof the IC increases due to the abnormal conditions suchas an instantaneous short-circuit of the SW pin. TSD does

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NR263S

9.5

Overcurrent Protection and Output
Short Circuit Protection

The IC has the overcurrent protection (OCP) circuitwith drooping characteristics as shown in Figure 9-8. The
OCP circuit detects the peak current flowing to the power
MOSFET in the IC by pulse-by-pulse. When this peakcurrent exceeds the OCP threshold value, on-period of thepower MOSFET is forcibly terminated. Thus, the output
voltage is decreased, and the output current is limited.
As shown in Figure 9-9, when the VO pin voltage
decreases from the setting value of 5 V, and reaches 3.50
V (70%), the IC transits to the switching frequency
reduction mode. This improves the drooping
characteristics.
Moreover, when the VO pin voltage decreases to 1.50
V (30%), the IC charges the soft-start capacitor, CSS of
the SS pin by ISS = −5.0 μA. When the SS pin voltage, VSS,
increases to 2.2 V or more, the output short circuit
protection is started. When the output short circuit
protection is started, the IC discharges CSS by current of
2.5 μA, and stops the switching operation until VSS

OutputCurrent,
IOUT

OCP

decreases to 0.23 V. When VSS decreases to 0.23 V, thesoft-start operation is restarted.
As described above, while the output short circuit
protection is operated, intermittent operation (hiccup) is
repeated. This intermittent operation reduces the stress ofparts such as heat generation. When the overcurrent stateis released, the output voltage returns automatically.

Output Voltage, VOUT (V)not guarantee the operation including the IC reliability inthe short-circuit state for long period or the state where
the heat generation continues.

6.0
5.0
4.0
3.0
2.0
1.0
0.0
0.0

0.5

1.0

1.5

2.0

Output Current, IOUT (A)Figure 9-8.

Overcurrent Protection Characteristic
Example (VIN = 12 V)

Short Circuit Protection

0t

SW PinVoltage0tHigh-side 2.1 A
Drain
Current
0t

VO PinVoltage0

1.5 V

SS PinVoltage

2.2 V

0SS PinCurrent

0.23 Vt

1.4 V
t

2.5 μA0t−5.0 μA

Figure 9-9.

Operational Waveforms of Overcurrent Protection and Output Short Circuit Protection

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NR263S
9.6

Pulse Skip Mode

The IC has the pulse skip mode to improve theefficiency in light load. The pulse skip mode cannot bedisabled by the external signal.
When the load current decreases, the IC controls so as
to decrease the output voltage of error amplifier, VCOMP(see Section 4). VCOMP cannot be checked directly fromthe outside of the IC. When the state where VCOMP is low
continues for a certain period, the IC switches the pulse
skip mode. In the pulse skip mode, the drain current peakvalue that flows the high-side MOSFET in the IC, ILP, islimited to the constant value. This limit value isdetermined by the input voltage, VIN, and the inductanceof the used inductor, L. The pulse skip frequency is varied
according to the load. When the state where VCOMP is
increased continues for a certain period by increasing theload current, the IC returns to the normal PWM operation.
Thus, the switching losses of high-side and low-side
MOSFETs in the IC are reduced by decreasing the pulse
skip frequency in light load.

When the pulse skip frequency decreases to the audible
frequency (20 kHz or less), note that the audible noise
may be generated in the actual operation. In this case,adjust the inductor value with reference to Equation (5).
The approximate pulse skip frequency, fSKIP, iscalculated by Equation (5).
fSKIP ≈

2 × IOUT × VOUT × (VIN − VOUT )(5)

ILP 2 × L × VIN

Where:IOUT is the output current (A),VOUT is the output voltage (fixed to 5 V internally),
VIN is the input voltage,
L is the inductance, and
ILP is the high-side drain current peak value in pulse
skip operation (Since ILP depends on the input voltage,
read the value of ILP from Figure 9-10, and substitute it.
The values in Figure 9-10 are reference, and are notguaranteed under the conditions requiring accuracy.)

1.2

L=6.8μH

High-side Drain Peak Current, ILP (A)L=10μH1.0

L=22μH
L=33μH0.8

L=47μH
L=68μH

0.6

0.4

0.2

0.0
5

10

15

20

25

30

35

Input Voltage, VIN (V)
Figure 9-10.

ILP Input Dependence (Reference Value)

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NR263S
10. Design Notes
10.1 Thermal Derating
Figure 10-1 shows the IC derating when mounting on
the board described in Section 0. When using the IC,
ensure enough margins.

Power Dissipation, PD (W)

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2

that a low leakage flux core (structure) is used. In the open
magnetic circuit core such as drum type, the peripheral
circuit may be damaged by noise because the magnetic
flux passes outside the coil. For details, contact inductor
manufacturer.
● DC Superimposed Characteristic
The inductance has the DC superimposed characteristic(i.e., the characteristic the inductance decreases as DC
increases). Be sure to check the maximum value of theactual flowing current whether the inductance issignificantly decreased from the design value. The
saturation point and the DC superimposed characteristic
should be confirmed after obtaining the characteristics of
the inductor to be used from the inductor manufacturer.
For example, when the maximum load is IOUT = 1 A, acoil with a saturation point of 0.5 A cannot be used.
Moreover, care should be taken when the inductor
characteristic with the inductance of 10 μH at no load is
5 μH at 1 A.

0.0
-40 -20 0

20 40 60 80 100 120 140 160

Ambient Temperature, TA (°C)
Figure 10-1.

Thermal Derating Curve

The IC loss is calculated by Equation (6). Since theefficiency, ηx, is varied depending on the input and output
voltages, substitute the appropriate value according to thepower supply specifications (see Figure 12-1).
100
PD = VOUT × IOUT (
− 1)
ηx

(6)

Where:
VOUT is the output voltage,
VIN is the input voltage,
IOUT is the output current, andηx is the efficiency (%).

10.2 External Components
Each part suitable for the usage condition should be
used.

● Inductor TemperatureSelf-heating of an inductor depends on the DC
resistance, DCR, of the winding. Reducing the winding
diameter increases the DC resistance (DCR) and causes
the inductor temperature rising. In general, there are thefollowing limitations depending on the inductor type:– Automotive grade product: 150 °C– Highly reliable product: 125 °C– General product: 85 °C to 100 °C
The inductor temperature is varied according to theheat dissipation conditions. Be sure to check the inductor
temperature including self-heating and temperature riseby heat generation of surrounding parts. Appropriate
inductor should be selected taking into account the usage
conditions, mounting conditions, and heat dissipation
conditions.
● ΔIL/IOUT Setting
When ΔIL/IOUT, which is the ratio of the inductor ripple
current (ΔIL) and the output current (IOUT), are large, theinductance decreases, but the output ripple voltage
increases. Decreasing ΔIL/IOUT increases the inductance,
and also increases the inductor size.

10.2.1 Inductor
For the regulator stable operation, it is required to avoid
saturating the inductor and self-heating excessively.
When choosing an inductor, care should be taken for thefollowing contents.
● Inductor TypeBe sure to choose an inductor for a switching regulator.
Using an inductor for noise filter is prohibited because theloss is large. For suppressing the noise effect to theperipheral circuit, it is recommended to use the inductor
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NR263S● Inductance Calculation
The IC adopts the peak detection current control
method. In this method, the problem of sub-harmonic
oscillation occurs in principle. The sub-harmonic
oscillation is a phenomenon that the inductor current
fluctuates with a cycle at an integral multiple of theswitching frequency. The sub-harmonic oscillation may
occur when the duty cycle reaches 0.5 or more in thecontinuous current mode. In order to avoid the subharmonic oscillation, the slope compensation is
performed inside the IC. However, since the slope
compensation amount is fixed inside the IC, the slope
compensation is not performed perfectly for rapid current
change. Therefore, the inductance must be set so that theslope of the inductor current is small. As shown inEquation (7) and Equation (8), the inductor ripple current,
ΔIL, and the inductor peak current, ILP, increase as theinductance is small, and the slope of the current waveform
also increases.
(VIN − VOUT ) × VOUT
L × VIN × fSW

(7)

ILP =

ΔIL
+ IOUT
2(8)

Where:
VIN is the input voltage,
VOUT is the output voltage (fixed to 5 V internally),
L is the inductance,
fSW is the switching frequency, and
IOUT is the output current (A).
High inductance

IOUT

Low inductance

ΔIL

ΔIL
ILP

0

Figure 10-2

(VIN − VOUT ) × VOUT
ΔIL × VIN × fSW(9)Where:
L is the inductance,
VIN is the input voltage,
VOUT is the output voltage (fixed to 5 V internally),
ΔIL is the ripple current (see Table 10-1), andfSW is the switching frequency.
Table 10-1. ΔIL Setting Value
Duty Cycle

Ripple Current, ΔIL

More than 0.5

Less than 0.2 A

Less than 0.5

More than 0.2 A, less than 1 A

10.2.2 Input/Output Capacitor

ΔIL =

IL

L≥

ILP
t

Relationship between Inductance andRipple Current

The inductance is set in the range of Equation (9).
The ripple current, ΔIL, in Equation (9) must be set
according to the duty cycle to avoid the sub-harmonic
oscillation (see Table 10-1). The duty cycle is determinedby VOUT/VIN, which is the ratio of the output voltage(VOUT) and the input voltage (VIN). Since the output
voltage of the IC is 5 V, the duty cycle reaches 0.5 or morewhen the input voltage is decreased to 10 V or less. The
inductance must be set to prevent the inductor from being
magnetically saturated even during overload or shortcircuit load condition.

To operate the IC stably, the input capacitor, CIN, must
be used a ceramic capacitor to decrease the input
impedance. In addition, CIN must be placed close to theIC, and be connected to the IN and GND pins with aminimum length of traces. Even when there is asmoothing capacitor for the rectifier circuit placed at the
input side of the IC, CIN is required to connect near the IC.
The output capacitor, COUT, is for smoothing of theswitching output. An LC low-pass filter consists of COUT
and inductor. The inductor ripple current, ΔIL, flows to
COUT. A low ESR ceramic capacitor can be used for COUT.
Conventionally, an electric capacitor with large
capacitance is required for the output to compensate thesecond delay of the LC filter. However, the mounting area
can be greatly reduced because the ceramic capacitor forthe output can be used in the IC with the current control
method.
The ceramic capacitor has the equivalent series resistor,
ESR. The output ripple voltage, VORIPPLE, is calculated by
the following equation.
VORIPPLE = ESR(COUT ) × ΔIL(10)

Where:ESR(COUT) is the equivalent series resistor of theoutput capacitor, and
ΔIL is the inductor ripple current.

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NR263S
When the output ripple voltage is set less than VORIPPLE,
the ESR requirements for ceramic capacitors are as
follows:
VORIPPLE
ESR(COUT ) <
ΔIL

RBS

U1
VIN

5

(11)

As shown in Equation (11), when ΔIL is large, theoutput ripple voltage, VORIPPLE, becomes relatively large.
To decrease ESR, the workaround such as connecting theceramic capacitors in parallel is required.
For the input capacitor, CIN, and the output capacitor,
COUT, must be selected the appropriate capacitor taking
into account enough margins for the usage, mounting, andheat dissipation conditions. In particular, care should betaken for the following contents (for details, contact
capacitor manufacturer).
● The breakdown voltage of the capacitor is sufficient for
the voltage range to be used.
● Change in capacitance is small in the voltage range tobe used.
● Change in capacitance is small in the temperature range
to be used.
● The capacitor temperature including a self-heating andan ambient temperature is within the maximum
operating temperature range of the capacitor.
(When the ripple current flows to the ceramic capacitor,
the capacitor temperature increases due to ESR.)● The impedance of the capacitor is sufficiently low
under the frequency and temperature conditions to be
used.

10.3 Spike Noise Reduction Methods
When measuring spike noises with an oscilloscope, thespike noises may be measured larger than the actual value
because the probe ground lead wire behaves as an antenna.
To suppress this, connect the ground lead wire of theprobe as short as possible, and connect it to the root of theoutput capacitor.
The spike noise reduction methods are described asfollows. Note that the circuit efficiency is decreased ineither method.
● Adding RBS
To slow down a turn-on switching speed of the internal
power MOSFET, add a resistor, RBS, between the BS andSW pins (see Figure 10-3). This reduces the spike noises.
RBS should be set 10 Ω or less. If the value of RBS is too
high, the startup failure or the damage by under drive stateof the power MOSFET may be caused.

2
BS

IN

CBS
VOUT

SW 3

L

GND
4

CIN

Figure 10-3.

COUT

Adding Series Resistor● Adding Snubber Circuit
To compensate the output waveform and the dioderecovery time, add a resistor and a capacitor (RC snubber)
between the SW and GND pins (see Figure 10-4). This
reduces the spike noise.
VIN 5

U1

L

SW 3

IN

GND

VOUT

About 10Ω

CIN

About 1000pF COUT
4

Figure 10-4.

Adding Snubber Circuit

10.4 For Applications Where Output
Voltage Is Higher than Input Voltage
For the applications where the SW pin voltage is higher
than the IN pin voltage (e.g., battery charger), add a diodefor reverse bias protection between the IN and SW pins.
D
VIN
CIN

Figure 10-5.

U1
5

SW 3

IN
GND
4

VOUT
L
COUT

Adding Reverse Bias Protection Diode10.5 For Applications Hot Swapping Load
Wire in Power Supply Operation
For applications where active wires such as load line
connectors connected to the output circuit are inserted andremoved while the switching regulator circuit is operating(i.e., hot swapping), add RVO so that the surge voltage by
hot swapping does not exceed the absolute maximum
rating (6 V) of the VO pin (see Figure 10-6). RVO
reference value is 100 Ω. Note that the output voltage (5V) increases when adding RVO (e.g., the output voltage
increases by about 5 mV when RVO = 100 Ω).

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NR263S
U1

L

SW 3

IN

CIN

VO

VOUT

RVO

7

About 100Ω

GND

COUT

4

Adding VO Pin Thermal Shutdown
Resistor, RVO

VIN

REN

6

5

CSS

1

2

IN
GND

NR263S
CIN

3

4

L

VOUT

CBS

COUT

Bead-core Insertion Prohibited Area

5

IN

EN

6

7

EN

8

Figure 10-9.

VO

7

NC

8

Bead-core Insertion
Prohibited Area

REN

VO

Since a large current flows to the bold line in Figure
10-7, the trace should be wide and short. Also, the control
ground must be separated from the ground where thelarge current flows, and should be connected to the rootof the output capacitor at a single point.
Since the ripple current flows to CIN and COUT, theimpedance of the trace between these capacitor electrodes
should be small. Therefore, the input capacitor, CIN, andthe output capacitor, COUT, must be placed as close as
possible to the IC, and be connected to each pin as short
as possible with thick trace (see Figure 10-8).

SW

10.6 PCB Layout

VIN

To operate the IC safety, a parasitic inductance of
wiring should be minimized. When inserting the bearcore such as ferrite bead in the shaded area of Figure 10-9,
the bead-core inductance is added to the parasitic
inductance of traces. The surge voltage generated by the
inductance on these traces may cause malfunction of theIC, and in the worst case, critical damage to the IC.
Therefore, do not insert the bead-core on the wiring in theshaded area of Figure 10-9.

BS

Figure 10-6.

10.7 Using Bead-core

NC

5

SS

VIN

BS
2

CSS

Figure 10-7.

SW

SS
1

GND

NR263S
CIN

3

4

L

CBS

VOUT
COUT

Large Current Pattern

Copper area(A) Low Impedance
Figure 10-8.

(B) High Impedance

Peripheral Layout Example of CIN and
COUT

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NR263S
11. Pattern Layout Example
Note that the pattern layout example only uses the parts illustrated in the circuit diagram below because this board isused for some other products.
Size: 40 mm × 40 mm
Thickness of the board: 1.6 mm
Copper thickness: 35 μm(A) Top View

(B) Bottom View
Figure 11-1.

Pattern Layout Example

Vin
U1

C3
C1

R3

C7

C2

1 SS

NC 8

2 BS

VO 7

3 SW

EN 6

4 GND

IN 5

R4
R1

R5
Vout

L1
R10

C4

C5

C13
GND

GND

Figure 11-2.

Circuit Diagram of Pattern Layout Example

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NR263S
Table 11-1. Reference Value (VIN = 12 V)
Symbol
C1
C2
C3
C4
C5
C7
C13
L1
R1
R3
R4
R5
R10
U1

Part
Chip ceramic capacitor
Chip ceramic capacitor
Chip ceramic capacitor
Chip ceramic capacitor
Chip ceramic capacitor
Chip ceramic capacitor
Chip ceramic capacitor
Inductor
Chip resistor
Chip resistor
Chip resistor
Chip resistor
Chip resistor
Buck converter

Reference Value
10 μF, 50 V, 3216
10 μF, 50 V, 3216
0.1 μF, 50 V, 1608
22 μF, 25 V, 3225
22 μF, 25 V, 3225
0.047 μF, 50 V, 1608
Open
6.8 μH
100 kΩ, 0.1 W, 1608
0 Ω, 1608
0 Ω, 1608
0 Ω, 1608
Open
SOP8

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Remarks

Low ESR type
Low ESR type
Adjustment capacitor
SLF12575T-6R8N5R9-PF (TDK)
Adjustment resistor
JumperJumperAdjustment resistor
NR263S (Sanken)

18

NR263S
12. Typical Characteristics
Unless otherwise specified, TA = 25 °C, VIN = 12 V, and VOUT = 5 V.
VIN = 8 V

100
90

Efficiency, η (%)c8070
VIN = 12 V

60

VIN = 18 V

50

VIN = 24 V

40

VIN = 31 V

30
20
10

0
0.001

0.010

0.100

1.000

Output Current, IOUT (A)Figure 12-1.

2.5
Input Current, IIN (mA)

6.0

Output Voltage, VOUT (V)Efficiency Curves

5.0
4.0

2

1.5

3.0
2.0

1

0.5

1.0

0.0
4.0

5.0

6.0

7.0

8.0

0

0

5

Input Voltage, VIN (V)
Figure 12-2.

Output Voltage Rising (IOUT = 1 A)

10

15

20

25

30

Input Voltage, VIN (V)
Figure 12-3.

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Input Current, IIN

19

5.20

10

5.15

9

5.10
5.05
5.00

4.95
4.90

4.85
4.80
0.0

0.2

0.4

0.6

0.8

1.0

Quiescent Circuit Current (μA)

Output Voltage, VOUT (V)NR263S

8

7
6
5
4
3
2

1
0
0

5

10

Output Current, IOUT (A)

20

25

30

Input Voltage, VIN (V)

Load Regulation

Figure 12-5.

Quiescent Circuit Current

6.0

1000

Output Voltage, VOUT (V)Operating Frequency, fOSC (kHz)

Figure 12-4.

15

100

10

1
0

0.2

0.4

0.6

0.8

1

5.0
4.0

VIN = 8 V
VIN = 12 V
VIN = 18 V

3.0
2.0

VIN = 31 V
VIN = 24 V

1.0
0.0
0.0

0.5

1.0

1.5

2.0

2.5

Output Current, IOUT (A)Output Current, IOUT (A)Figure 12-6.

Operating Frequency

Figure 12-7.

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Overcurrent Protection Characteristics

20

NR263S

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and its control systems, traffic signal control systems or equipment, disaster/crime alarm systems, various safety devices, etc.), youmust contact a Sanken sales representative to discuss the suitability of such use and put your signature, or affix your name and seal,on the specification documents of the Sanken Products and return them to Sanken, prior to the use of the Sanken Products. The
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DSGN-CEZ-16003

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