BD3523HFN, BD35230HFN, BD35231HFN
Technical Note
15/20
www.rohm.com
2009.04 - Rev.B
© 2009 ROHM Co., Ltd. All rights reserved.
●Recommended Circuit Example (BD3523HFN)
Component
Recommended
Value
Programming Notes and Precautions
R1/R2 3.3k /3.9k
IC output voltage can be set with a configuration formula V
FB×(R1+R2)/R7 using the values
for the internal reference output voltage (VFB) and the output voltage resistors (R6, R7).
Select resistance values that will avoid the impact of the FB bias current (±100nA). The
recommended total resistance value is 10kΩ.
C3 22μF
To assure output voltage stability, please be certain the output capacitors are connected
between Vo1, Vo2, Vo3 pin and GND. 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 47μF
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/ C2 1μF/22μF
Input capacitors reduce the output impedance of the voltage supply source connected to the
input pin (V
CC,). 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.
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.
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.
6
V
cc
EN
VIN
4
3
2
1
V
o
V
o
8
7
6
5
GND
FB
NRCS
C1
V
cc
R4
EN
C4
VIN
C2
R2
R1
C3
GND
FB
V
o
C5
