R1224N122G RICOH [RICOH electronics devices division], R1224N122G Datasheet - Page 9

• Manufacturer Part Number: R1224N122G
• Description: PWM/VFM step-down DC/DC Converter
• Manufacturer: RICOH [RICOH electronics devices division]

How to Adjust Output Voltage and about Phase Compensation
As for Adjustable Output type, feedback pin (V
Output Voltage, V
Thus, with changing the value of R2 and R4, output voltage can be set in the specified range.
In the DC/DC converter, with the load current and external components such as L and C, phase might be behind
180 degree. In this case, the phase margin of the system will be less and stability will be worse. To prevent this,
phase margin should be secured with proceeding the phase. A pole is formed with external components L and
C3.
A zero (signal back to zero) is formed with R4 and C4.
For example, if L=27µH, C3=47µF, the cut off frequency of the pole is approximately 4.5kHz.
To make the cut off frequency of the pole as much as 4.5kHz, set R4=33kΩ and C4=1000pF.
If V
R3 prevents feedback of the noise to V
OUT
is set at 2.5V, R2=22kΩ is appropriate.
V
V
≅Fzero~1/(2π×R4×C4)
Fpole
OUT
OUT
: R2+R4=V
=V
~
FB
1/2
OUT
×(R2+R4)/R2
R1
π
is as following equation:
L
FB
×
C3
: R2
C1
C2
5
1
V
CE
CE CONTROL
IN
FB
pin, about 2.7kΩ is appropriate value.
R1224N
FB
GND
EXT
4
2
) voltage is controlled to maintain 1.0V.
PMOS
V
FB
3
SD
L
R4
R2
R3
C4
LOAD
C3
R1224N
9