BD3540NUV, BD3541NUV

Technical Note

11/16

www.rohm.com

2009.04 - Rev.B

© 2009 ROHM Co., Ltd. All rights reserved.

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Recommended Circuit Example

Component

Recommended

Value

Programming Notes and Precautions

R1/R2

3.9k/3.3k

IC output voltage can be set with a configuration formula using the values for the internal

values that will avoid the impact of the VREF current (±100nA). The recommended total

resistance value is 10KΩ.

C3

22μF

To assure output voltage stability, please be certain the VOUT1 pins and the GND pins are

connected. Output capacitors play a role in loop gain phase compensation and in

mitigating output fluctuation during rapid changes in load level. Insufficient capacitance

may cause oscillation, while high equivalent series reisistance (ESR) will exacerbate

output voltage fluctuation under rapid load change conditions. While a 22μF ceramic

capacitor is recomended, actual stability is highly dependent on temperature and load

conditions. Also, note that connecting different types of capacitors in series may result in

insufficient total phase compensation, thus causing oscillation. In light of this information,

please confirm operation across a variety of temperature and load conditions.

C1

1μF

Input capacitors reduce the output impedance of the voltage supply source connected to

the (VCC) input pins. If the impedance of this power supply were to increase, input voltage

(VCC) could become unstable, leading to oscillation or lowered ripple rejection function.

While a low-ESR 1μF capacitor with minimal susceptibility to temperature is

recommended, stability is highly dependent on the input power supply characteristics and

the substrate wiring pattern. In light of this information, please confirm operation across a

variety of temperature and load conditions.

C2

22μF

Input capacitors reduce the output impedance of the voltage supply source connected to

the (VIN) input pins. If the impedance of this power supply were to increase, input voltage

(VIN) could become unstable, leading to oscillation or lowered ripple rejection function.

While a low-ESR 22μF capacitor with minimal susceptibility to temperature is

recommended, stability is highly dependent on the input power supply characteristics and

the substrate wiring pattern. In light of this information, please confirm operation across a

variety of temperature and load conditions.

C4

0.01μF

The Non Rush Current on Startup (NRCS) function is built into the IC to prevent rush

current from going through the load (VIN to VO) and impacting output capacitors at power

supply start-up. Constant current comes from the NRCS pin when EN is HIGH or the UVLO

function is deactivated. The temporary reference voltage is proportionate to time, due to

the current charge of the NRCS pin capacitor, and output voltage start-up is proportionate

to this reference voltage. Capacitors with low susceptibility to temperature are

recommended, in order to assure a stable soft-start time.

C5

-

This component is employed when the C3 capacitor causes, or may cause, oscillation. It

provides more precise internal phase correction.

R5

100k

It is pull-up resistance of Open Drain pin. 100kΩ is recommended.

R4

Several kΩ

～

several 10kΩ

It is recommended that a resistance (several kΩ to several 10kΩ) be put in R4, in case

negative voltage is applied in EN pin.

1

2

3

4

10

9

8

7

VOUT1(1.2V)

C3

R2

R1

FB

C4

GND

VCC

C1

EN

C2

VIN

R4

C5

6

5

VCC

R5

C6