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參數(shù)資料
| 型號： | RT9209GS |
| 廠商： | Richtek Technology Corporation |
| 英文描述： | Synchronous Buck PWM DC-DC with Enable & PGOOD |
| 中文描述： | 同步降壓PWM直流與直流啟用 |
| 文件頁數(shù)： | 12/14頁 |
| 文件大小： | 217K |
| 代理商： | RT9209GS |
RT9209/A
12
DS9209/A-08 March 2007
www.richtek.com
F
(
V
OUT
(V)
4
3.5
3
1
1.5
2
2.5
0.82
0.78
0.80
0.81
0.79
0.5
4.5
VIN = 5V
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
manufacturer 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 RT9209/A 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 1.6V, the loop
gain and loop pole/zero are calculated as follows :
The RT9209/A Bode plot as shown Figure 5 is stable in
most of application conditions.
Figure 5
Figure 6
Figure 7
Loop Gain
40
30
20
10
1M
10k
1k
100
100k
V
OUT
= 3.3V
C
= 1500uF(33m
Ω
)
L = 2uH
V
OUT
= 1.5V
V
OUT
= 2.5V
V
OUT
= 3.3V
P
O
= 2.9kHz
Z
O
= 3.2kHz
π
π
×
×
×
×
×
×
A
OUT
O
O
5
0.8
DC loop gain G = 35 dB
1.6
V
1
LC filter pole P =
LC
2
Error Amp pole P = 300kHz
1
ESR zero Z =
ESR C
2
Reference Voltage
Because RT9209/A use a low 35dB gain error amplifier,
shown in Figure 6. The voltage regulation is dependent
on V
IN
& V
OUT
setting. The FB reference voltage of 0.8V
were trimmed at V
IN
= 5V & V
OUT
= 2.5V condition. In a
fixed V
IN
= 5V application, the FB reference voltage vs.
V
OUT
voltage can be calculated as Figure 7.
Feedback Divider
The reference of RT9209/A is 0.8V. The output voltage can
be set using a resistor based divider as shown in Figure 8.
Put the R1 and R2 as close as possible to FB pin and R2
should less than 1 k
Ω
to avoid noise coupling.
Figure 8
+
C
OUT
V
OUT
R1
R2
L
VIN
RT9209/A
FB
A
+
+
-
PWM
R2
56K
R1
1K
+
-
FB
REF
0.8V
RAMP
1.75V
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| RT9210PC | 制造商:RICHTEK 制造商全稱:Richtek Technology Corporation 功能描述:Dual 5V Synchronous Buck DC-DC PWM Controller for DDR Memory VDDQ and VTT Termination |
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