BD3550HFN_08 Datasheet, PDF (11/17 Pages) Rohm – Ultra Low Dropout Linear Regulators for PC

●Recommended Circuit Example
VCC
EN
1
C1
2
R4
3
4
VIN
C2
8
GND
7
C4
6
R1
5 ^R2
FB
C5
VOUT1(1.2V)
C3
Component
R1/R2
C3
C1
C2
C4
C5
R4
Recommended
Value
3.9k/3.3k
22μF
1μF
22μF
0.01μF
-
Several kΩ
～several 10kΩ
Programming Notes and Precautions
IC output voltage can be set with a configuration formula using the values for the internal
reference output voltage (V_FB)and the output voltage resistors (R1, R2). Select resistance
values that will avoid the impact of the VREF current (±100nA). The recommended total
resistance value is 10KΩ.
To assure output voltage stability, please be certain the Vo1, Vo2, and Vo3 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.
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 1 μ F 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.
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 22 μ F 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.
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.
This component is employed when the C3 capacitor causes, or may cause, oscillation. It
provides more precise internal phase correction.
It is recommended that a resistance (several kΩ to several 10kΩ) be put in R4, in case
negative voltage is applied in EN pin.
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