RT9206GS Richtek USA Inc, RT9206GS Datasheet - Page 17

• 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

V
IN
V
DS9206-12 April 2008
From control system point of view, the block diagram of
Figure 5 is shown in Figure 6.
REF
First, deriving the accurate small-signal models of power
stage, the equation (18) is the transfer function of
v
technique.
G
Figure 5. The simplified diagram for synchronous Buck
O
P(S)
Figure 6. The control block diagram of synchronous
(s)/d(s), which be obtained by space averaging
i
+
S1
=
-
V
Generator
OUT(S)
PWM
d
d
(S)
S1
Compensator
-
+
converter and control loop.
S2
=
C(s)
S
2
Buck converter
x
Vc(s)
Sensor Gain
L
i
S2
Ra+Rb
x
Compensator
Rb
C
+ V
1
V
O
L
+
C
Generator
L
Cc2
+
rc x
-
PWM
1/Vr
S(
H (s)
V
R
V
C
+
OC
i
L
L
-
+
OR
-
L
O
Rc1
Cc1
d(s)
+
G(S)
x
rc x
S
r
C
C
i
C
OUT
gm
Converter
Gp(s)
C
BUCK
+
-
R
O
L
V
)
REF
+
V
1
I
Rb
OUT
OUT
Ra
+
-
x V
(18)
V
Sensor
OUT
IN
Gain
In Figure 7, the resonance of the output LC filter produces
a double pole and −40dB/decade slop. The resonance
frequency is expressed as follows :
Next, deriving the transfer function d(s)/v
duty ratio pulse-width modulator (PWM Generator). The
transfer function T
where, V
in datasheet.
For simplification, the transfer function of PWM generator
and Buck
in equation (20)
The transfer function of Equation (20) is a second order
system and Bode plot is shown in Figure 7.
G
(S)
T
f
P
m(S)
Phase
=
=
VIN/Vr
Figure 7. The Bode plot of Buck power stage
2
V
-180°
=
π
-90°
V
OUT(S)
r
0°
converter can is combined. The
C(S)
is the amplitude of ramp-waveform which is listed
V
x
d
C(S)
(S)
Gain
1
L
=
x
=
S
C
Vr
m
2
O
1
fp
(s) of the modulator
x
L
+
C
1
O
+
x
rc x
S(
fz
R
C
L
L
O
+
x
rc x
S
RT9206
resulting is shown
C
is given by
www.richtek.com
(s) of the direct
C
(Hz)
O
)
+
1
x
f
f
V
Vr
(21)
(19)
(20)
IN
17