RT9202BGS RICHTEK [Richtek Technology Corporation], RT9202BGS Datasheet - Page 11

• Manufacturer Part Number: RT9202BGS
• Description: Single Synchronous Buck PWM DC-DC Controller
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Table 1
*Refer to Sanyo low ESR series (CE, DX, PX.....)
The suggested L and C are as follows:
2
5 H with 1000 F C
DS9202B-03 March 2007
1000 F (ESR=53m )
1500 F (ESR=33m )
3000 F (ESR=21m )
H with 1500 F C
C.C.M
V
i
i
V
Q
I
L
i
D
L
Inductor
V
OUT
T
ON
Q
T
S
V
I
D
T
- V
OUT
OUT
OFF
mI
O
L
Figure 5
V
- V
L
100mV
L
62mV
40mV
2 H
O
C
3.3V
uQ
R
40mV
25mV
16mV
5 H
V
O
I
I
I
L
Q
D
= I
110mV
O
68mV
43mV
2 H
2.5V
44mV
28mV
18mV
5 H
Input / Output Capacitor
High frequency/long life decoupling capacitors should be
placed as close to the power pins of the load as physically
possible. Be careful not to add inductance to the PCB
trace, as it could eliminate the performance from utilizing
these low inductance components. Consult with the
manuf acturer of the load on specific decoupling
requirements.
The output capacitors are necessary for filtering output
and stabilizing the close loop (see the PWM loop stability).
For powering advanced, high-speed processors, it is
required to meet with the requirement of fast load
transient, high frequency capacitors with low ESR/ESL
capacitors are recommended.
Another concern is high ESR induced ripple may trigger
UV or OV protections.
PWM Loop Stability
The RT9202B is a voltage mode buck controller designed
for 5V step-down applications. The gain of error amplifier
is fixed at 35dB for simplified design.
The output amplitude of ramp oscillator is 1.75V, the loop
gain and loop pole/zero are calculated as follows :
DC loop gain G
LC filter pole P
Error Amp pole P
ESR zero Z
The RT9202B Bode plot as shown Figure 6 is stable in
most of application conditions.
93mV
58mV
37mV
2 H
O
=
1.5V
O
A
2
=
=
A
= 300kHz
35dB
2
ESRC
37mV
23mV
15mV
5 H
1
1
LC
1.75
5
V
0.8
OUT
RT9202B
www.richtek.com
11