BD9137MUV Datasheet, PDF (11/17 Pages) Rohm – High Efficiency Step-down Switching Regulator

Rf
Cf
VCC
Cin
EN
PVCC
VCC
CBST
VOUT
ADJ
L
ITH
GND,PGND
SW
VOUT
RITH
ESR
RO
CITH
CO
Fig.32 Typical application
Stable feedback loop may be achieved by canceling the pole fp (Min.) produced by the output capacitor and the load resistance
with CR zero correction by the error amplifier.
fz(Amp.)= fp(Min.)
1
2π×RITH×CITH
=
1
2π×ROMax.×CO
5. Determination of output voltage
The output voltage VOUT is determined by the equation (6):
VOUT=(R2/R1+1)×VADJ・・・(6) VADJ: Voltage at ADJ terminal (0.8V Typ.)
With R1 and R2 adjusted, the output voltage may be determined as required.
Adjustable output voltage range : 0.8V～3.3V
6
SW
1
ADJ
L
Co
Output
R2
R1
Fig.33 Determination of output voltage
Use 1 kΩ～100 kΩ resistor for R1. If a resistor of the resistance higher than 100 kΩ is used, check the assembled set carefully
for ripple voltage etc.
3.7
The lower limit of input voltage depends on the output voltage.
Basically, it is recommended to use in the condition :
VCCmin = VOUT+1.2V.
Fig.34. shows the necessary output current value at the lower
limit of input voltage. (DCR of inductor : 20mΩ)
This data is the characteristic value, so it’ doesn’t guarantee the
operation range,
3.5
Vo=2.5V
3.3
Vo=2.0V
3.1
Vo=1.8V
2.9
2.7
0
1
2
3
OUTPUT CURRENT : IOUT[A]
Fig.34 minimum input voltage in each output voltage
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