RT9206GS Richtek USA Inc, RT9206GS Datasheet - Page 18

• Manufacturer Part Number: RT9206GS
• Description: IC CTRLR DUAL SYNC BUCK 16SOP
• Manufacturer: Richtek USA Inc

Specifications of RT9206GS

• Topology: Step-Down (Buck) Synchronous (1), Linear (LDO) (2)
• Function: Any Function
• Number Of Outputs: 3
• Frequency - Switching: 200kHz ~ 600kHz
• Voltage/current - Output 1: Controller
• Voltage/current - Output 2: Controller
• Voltage/current - Output 3: Controller
• W/led Driver: No
• W/supervisor: No
• W/sequencer: No
• Voltage - Supply: 4.75 V ~ 28 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RT9206
The Effective Series Resistance (ESR) of capacitor and
capacitance introduces one zero into system, the zero is
given as :
In the voltage-mode Buck converter shown in Figure 5, the
loop gain of system is
The desired loop gain and phase margin is show in the
Bode plot of Figure 8.
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18
Figure 8. The Bode plot of desired loop gain and phase
T
f
Z
L(S)
VIN/Vr
Phase
-180 °
TL(s)
-90 °
2
0°
Gain
C
G(s)
x
(S)
rc x
1
x
Vr
C
1
O
fp
x
Power
stage
G
(Hz)
loop gain
P(S)
Desired
margin
x
H
fz
(S)
fc
C
(S)
x
margin
Phase
G
(S)
x
H
(S)
f
f
f
(22)
(23)
Where the f
frequency when the loop gain equals unity. Typically, f
chosen in range 1/10 to 1/20 of switching frequency. f
determines how fast the dynamic load response is. The
higher f
margin in the range of 45 to 60 is desirable.
So, the transfer function of compensator C(s) must be
designed to meet these requirements. In many applications,
use an electrolytic capacitor as the output capacitor, if the
zero (f
capacitor is a few kHz and smaller than 8 times f
type 2 (PI) can be used to get desired compensation. Figure
9 shows the typical type 2 trans-conductance error
amplifier and the Bode plot is also shown in Figure 10.
Figure 10. The Bode plot of type 2 trans-conductance
Figure 9. The typical type 2 trans-conductance error
Z
) caused by Effective Series Resistance (ESR) of
C
gmRc1
with the faster dynamic response, and the phase
Ra
Rb
-90
C
V
OUT
is zero crossover frequency defined as the
Gain(dB)
Phase
V
REF
error amplifier
fcz
amplifier.
+
-
gm
Boost
DS9206-12 April 2008
Rc1
Cc1
Vc
fcp
Cc2
f
f
P
, the
C
be
C