RT9206GS Richtek USA Inc, RT9206GS Datasheet - Page 19

• 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

The design procedure as following :
(1). Selecting the zero crossover frequency f
(2). Place the zero of compensator is 70% fp that is
Design example
Design example of type 2 compensator: the schematic is
shown in Figure 4, where the parameters as following : V
= 12V, V
200kHz, L = 15 H, C
parameters of RT9206 as following : gm = 1.6ms, ramp
amplitude = 1.9V, and reference voltage Vref = 0.8V.
Step1. Determine the power stage poles and zeros. The
pole caused by the output inductor and output capacitor is
calculated as :
DS9206-12 April 2008
(3). Set a second pole to suppress the switching noise.
R
C =
C
f =
f =
P
Z
1/20 switching frequency. Then according equation (24)
set the resistor R
frequency.
resonance frequency of power stage. The compensator
capacitor Cc1 can be selected to set the zero. The
equation is shown in following :
C1
C2
C1
Assume the pole is one half of switching frequency
f
s
, which results in capacitor Cc2 as shows in following:
=
2
2
0.7 R
V
OUT
L C
Vr L f
IN
L C
r
1
1
R
C
C1
= 5V, I
gm r
O
C1
C
O
1
O
fs -
=
=
(F)
C
2
C1
C
C
2
OUT
1
C1
to determine the zero crossover
15
O
V
V
= 5A, switching frequency =
22mΩ 940 F
OUT
REF
= 940 F, r
1
1
940
R
( )
1
C1
fs
= 1.34kHz
C
(F)
= 22m , the
= 7.7kHz
C
is 1/10 to
(25)
(26)
(24)
IN
Step2. Determine the zero crossover frequency and
Select desired zero-crossover frequency :
Step3. Determine desired location of poles and zeros for
Select:
Assume
Step4. Calculate the real parameters-resistor and
From equation (21), the R
Select R
Calculate C
Select C
Second capacitor C
(26)
Select C
Select f
f
R
=
C
C
C
C1
C2
C 1
22m
20kH z 15 H 1.9
f /10 ~ f /20
=
S
=
f
compensated type.
type2 compensator.
CZ
capacitors for type2 compensator.
0.7 R
f
C2
C1
C1
CP
r
C
L C
C
= 0.7 f = 0.7 1.34kHz = 938Hz
f
= 22nF
= 220pF
= 8.2k
C1
C
= 20kHz
=
R
V
12V 1.6m s
from equation (25)
C1
1
f
2
S
S
O
L
C1
IN
= 100kHz
=
f
P
S
Vr
gm
C2
15
0.7 8.2k
can be calculated using equation
C1
V
V
8.2k
940
O U T
R E F
is calculated as following :
0.8V
5V
1
= 20.7nF
200kHz
= 8.4k
RT9206
www.richtek.com
194pF
19