rt9232b Richtek Technology Corporation, rt9232b Datasheet - Page 13

• Manufacturer Part Number: rt9232b
• Description: Programmable Frequency Synchronous Buck Controller
• Manufacturer: Richtek Technology Corporation

Feedback Loop Design Procedure
Use these guidelines for locating the poles and zeros of
the compensation network :
1. Pick Gain (R2/R1) for desired 0dB crossing frequency
2. Place 1
3. Place 2
4. Place 1
5. Place 2
6. Check gain against error amplifier's open-loop gain.
7. Pick R
8. Estimate phase margin and repeat if necessary.
Layout Consideration
Layout is very important in high frequency switching
converter design. If designed improperly, the PCB could
radiate excessive noise and contribute to the converter
instability. First, place the PWM power stage components.
Mount all the power components and connections in the
top layer with wide copper areas. The MOSFETs of Buck,
inductor, and output capacitor should be as close to each
other as possible. This can reduce the radiation of EMI
due to the high frequency current loop. If the output
capacitors are placed in parallel to reduce the ESR of
capacitor, equal sharing ripple current should be
considered. Place the input capacitor directly to the drain
DS9232B-03 March 2007
(F
(~75% F
100
-20
-40
-60
C
80
60
40
20
0
).
10
FB
20LOG
(R1/R2)
ST
ND
ND
ST
LC
for desired output voltage.
zero F
).
pole F
zero F
pole F
Modulator
100
Gain
Z1
Z1
Z2
Z2
1K
below modulator's double pole F
F
at the ESR zero F
at half the switching frequency.
at modulator's double pole F
Z1
F
Figure 3
LC
F
Frequency (Hz)
Z2
10K
F
20LOG
(V
P1
F
IN
ESR
/ΔV
100K
F
P2
OSC
)
Z_ESR.
Open Loop Error
AMP Gain
Closed Loop Gain
1M
Compensation
Gain
10M
LC
.
LC
of high-side MOSFET. The MOSFETs of linear regulator
should have wide pad to dissipate the heat. In multilayer
PCB, use one layer as power ground and have a separate
control signal ground as the reference of the all signal. To
avoid the signal ground is effect by noise and have best
load regulation, it should be connected to the ground
terminal of output. Furthermore, follows below guidelines
can get better performance of IC :
(1). The IC needs a bypassing ceramic capacitor as a R-C
(2). Place the high frequency ceramic decoupling close
(3). The feedback part should be placed as close to IC as
(4). The components of bootstraps should be closed to
(5).The PCB trace from Ug and Lg of controller to
(6). Place all of the components as close to IC as possible.
filter to isolate the pulse current from power stage
and supply to IC, so the ceramic capacitor should be
placed adjacent to the IC.
to the power MOSFETs.
possible and keep away from the inductor and all noise
sources.
each other and close to MOSFETs.
MOSFETs should be as short as possible and can
carry 1A peak current.
RT9232B
www.richtek.com
13