RT9206GS Richtek USA Inc, RT9206GS Datasheet - Page 16

• 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
For the example of C
T
Shutdown
The power stage can be shutdown by pulling soft-start pin
below 0.7V. During shutdown, both of high side MOSFET
(S1) and low side MOSFET (S2) are turned off.
Setting the switching frequency
The switching frequency can be set by a resistor (R
connecting between RT and GND pins. Equation (16)
describes the relationship of R
As R
www.richtek.com
16
VR
R
RT
Figure 4. The soft-stat timing diagram of RT9206
= 57ms, T
T
open the normally operated frequency is 200kHz.
=
f - 200 10
S
62 10
T
T
VR
SS
×
SS
R
×
f
= 133ms and T
RT
S
8
250
300
350
400
450
500
550
600
(kHz)
T
RT and GND Pins
PGOOD
Connecting Between
3
SS
= 1μF, V
(Ω)
RT
R
IN
PGOOD
and switching frequency.
RT
37.5
30.6
24.4
22.5
19.3
16.8
= 12V, V
120
55
(kΩ)
= 640ms.
OUT
V
V
V
PGOOD
SS
DD
OUT
= 5V, then
(16)
RT
)
Boost Component Selection
The booststrap gate drive circuit is used to drive high side
N-channel MOSFET. The boost capacitor should be a good
quality and can operate in high frequency. The value of
boost capacitor depends on the total gate charge (Q
turn on the MOSFETs. Assuming steady state operation,
the following equation can be used to calculate the
capacitance value to achieve the targeted ripple voltage
Δ V
The capacitor in the range of 0.1μF to 1μF is generally
adequate for most applications.
The VINT pin bypass capacitor C
boost capacitor, to drive the low side MOSFET, and to power
the RT9206. C
with short and wide traces. Generally, a 4.7μF high
frequency ceramic capacitor is recommended.
Feedback Compensation
The RT9206 is a voltage mode controller. The control loop
is a single voltage feedback loop including a trans-
conductance error amplifier and a PWM comparator.
To achieve fast transient response and accurate output
regulation, appropriate feedback compensation is
necessary. The goal of the compensation network is to
provide a closed loop transfer function with the highest
0dB crossing frequency and adequate phase margin.
Generally, the phase margin in a range of 45° to 60° is
desirable. Figure 4 shows the simplified diagram of
synchronous buck converter and control loop.
C
BOOT
BOOT
.
=
ΔV
Q
BOOT
INT
Hg
should locate near VINT and GND pins
INT
DS9206-12 April 2008
needs to charge the
H
g) to
(F)