RT9206
High Efficiency, Synchronous Buck with Dual Linear
Controllers
General Description
The RT9206 is a low cost, combo power controller, which
integrates a synchronous step-down voltage-mode PWM
and two HV linear controllers. Directly drive external
N-MOSFET makes it easy to implement a high efficiency
and cost attractive power solution. Voltage mode control
loop and constant operation frequency with external
compensation network provide better stability in wide
operation range. Adjustable operation frequency up to
600kHz can minimize the inductor size and PCB space. It
is particularly suitable in wide input voltage range (from
4.75V to 28V) and multi-output applications.
Linear controller features flexible linear power design.
Delivered power can be simply decided by external
N-MOSFET selection. Output voltage level is chosen via
external resistor divider. The 0.8V internal reference can
satisfy most of the applications. Under voltage lockout
provide cost effective protection of output.
RT9206 provides complete safety protection function: soft
start, over current protection, over voltage and under voltage
protection. Set current limit by choosing different MOSFET.
Synchronous Buck control mode provides excellent over
voltage protection by turning on low side MOSFET to
prevent any damage of end device from abnormal voltage
stress as over voltage condition occurs.
Features
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Wide Input Range (4.75V to 28V)
0.8V Internal Reference
High Efficiency Synchronous Buck Topology
Integrate two HV Linear Controllers
Low cost N-MOSFET Design
Duty Cycle from 0% to 90%.
Adjustable switching frequency from 200kHz to
600kHz, Default 200kHz
Sense OCP by low Side MOSFET R
DS(ON)
Power Good Signal Output
RoHS Compliant and 100% Lead (Pb)-Free
Applications
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LCD Monitor
Desk Note
IEEE1394 Client
Desktop IA
Broadband
Pin Configurations
(TOP VIEW)
LDRV1
VDD
LDRV2
LFB2
COMP
FB
PGOOD
SS/EN
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LFB1
BOOT
UGATE
PHS
VINT
LGATE
GND
RT
Ordering Information
RT9206
Package Type
S : SOP-16
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
}
SOP-16
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
}
DS9206-13 April 2011
www.richtek.com
1
RT9206
Typical Application Circuit
R1 10
C1
1µF
C15 500pF
R2 11k
V
OUT1
V
OUT2
3.3V
Q3
C16 500pF
C6
10µF
V
OUT3
2.5V
C7
10µF
Q4
R3 11k
R11
5.6k
C14
33nF
R12
4.3K
390pF
C13
R4
3.3k
D11N4148
15 R
BOOT
0 R13
C2
1µF
C3
220µF
V
IN
12V
1
2
3
4
5
6
7
8
R10
51k
LDRV1
LFB1
RT9206
15
VDD
BOOT
14
LDRV2
UGATE
13
LFB2
PHS
12
COMP
VINT
11
FB
LGATE
10
PGOOD
GND
9
SS/EN
RT
Q5
EN
16
C9
1µF
Si4800BDY
Q1 L1
C10
1000µF
4.7uH
Q2
C17
1000µF
C11
1µF
V
OUT1
5V
C8 4.7µF
0
R14
R
RT
R8
3k
R9
560
1µF
C
SS
PGOOD
Figure 1. Typical Application for 12V Input
R1 10
C1
1µF
C15 500pF
R2 11k
Q3
C16 500pF
C6
10µF
V
OUT3
2.5V
C7
10µF
Q4
R3 11k
R11
5.6k
C14
33nF
R12
8.2K
220pF
C13
R4
3.3k
D11N4148
15 R
BOOT
0 R13
C2
1µF
C3
220µF
V
IN
24V
V
OUT1
V
OUT2
3.3V
1
2
3
4
5
6
7
8
R10
51k
LFB1
LDRV1
RT9206
15
BOOT
VDD
14
LDRV2
UGATE
13
PHS
LFB2
12
COMP
VINT
11
LGATE
FB
10
GND
PGOOD
9
SS/EN
RT
Q5
EN
16
C9
1µF
Si4800BDY
Q1
C10
L1
1000µF
33µH
Q2
C11
1µF
V
OUT1
5V
C8 4.7µF
0
R14
R
RT
R8
3k
R9
560
4.7µF
C
SS
PGOOD
Figure 2. Typical Application for 24V Input
Note : R
BOOT
is a must to suppress ringing spike.
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2
DS9206-13 April 2011
RT9206
Function Block Diagram
LFB1
LFB2
VDD
0.6V
+
UV
-
0.6V
0.6V
COMP
0.8V
FB
+
GM
-
RAMP
Generator
+
OVP
-
-
PG
+
OSC
RT
+
PWM
-
CP
+
UV
-
+
UV
-
Driver
Control
Logic
0.8V
LCTR2
+
-
+
0.8V
+
-
+
LCTR1
LDRV1
LDRV2
6.0V
Reg
Thermal
Protection
BOOT
UGATE
PHS
VINT
LGATE
GND
VINT
Soft Start
SS/EN
8uA
PGOOD
1V
0.72V
DS9206-13 April 2011
www.richtek.com
3
RT9206
Operation
Introduction
The RT9206 is a combo controller, which integrates an
adjustable frequency, voltage mode synchronous step
down controller and two HV linear controllers. The
synchronous step down controller consists of an internal
precision reference, an internal oscillator, an error amplifier,
a PWM comparator, control logic and floating gate driver,
a programmable soft-start, a power good indicator, an over
voltage protection, an over temperature protection and short
circuit protection.
The output voltage of the synchronous converter is set
and controlled by the output of the error amplifier, which is
the amplified error signal from the sensed output voltage
and the voltage on non-inverting input, which is connected
with internal 0.8V reference voltage. The amplified error
signal is compared to a fixed frequency linear sawtooth
ramp and generates fixed frequency pulse of variable duty-
cycle, which drivers the two N-Channel external MOSFETs.
The timing of the synchronous converter is provide through
an internal oscillator circuit and can be programmed
between 200kHz to 600kHz via an external resistor
connected between RT pin and ground.
Soft-Start
RT9206 has a programmable soft-start to control the output
voltage rise time and limit the current surge at the start-
up. The soft-start will begin while V
DD
rises above POR
threshold for correct start-up. Soft-start function operates
by an internal sourcing current to charge an external
capacitor to around the voltage of VINT. The soft-start signal,
SS pin, is the third input non-inverting input of the PWM
comparator. Before soft-start signal reach the bottom of
the sawtooth ramp, inverting input of the PWM comparator,
the soft-start current is twice of the normal soft-start current.
Once the soft-start signal reach the bottom of the ramp,
the soft-start current became normal, and start to increase
duty cycle from zero to the point the feedback loop takes
control.
Power On Reset (POR)
The power on reset circuit assures that the MOSFET driver
outputs remain in the off state whenever the V
DD
supply
voltages lower than the POR threshold.
Over Current Protection
Whenever the over-current is occurred in soft-start or in
normal operation period, It will shut down PWM signal,
the MOSFET driver outputs remain in the off state, and
latch soft-start signal low until restart V
DD
supply voltage.
Over Voltage Protection
Once over-voltage protection occurred, it will turn on low
side MOSFET and latch soft-start signal low to prevent
end device form abnormal voltage stress. Restart V
DD
supply voltage will release the protection.
Power Good Indicator
The power good indicator is an open drain output to show
whether the synchronous converter output ready or not.
The power good indicator is available after soft-start end.
Short-Circuit Protection
The short-circuit phenomenon is sensed by the drop of
output voltage, synchronous converter and two linear
controller. Once the short-circuit occurred, the drop of output
voltage lower than the under voltage threshold, 0.6V on
feedback, the PWM signal will shut down and both of the
external MOSFET will turn off and soft-start signal latch
low. Soft-start signal, SS, is also connected to two linear
controller error amplifier non-inverting input. Therefore,
whenever the drop of output of the synchronous converter
or two linear controllers lower than under voltage threshold,
all MOSFET drivers will turn off.
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DS9206-13 April 2011
RT9206
Pin Description
LDRV1(Pin 1)
Linear controller 1 (LCTR1) driver. Connect to the gate of
external N-Channel MOSFET pass transistor to form a
positive linear regulator
VDD (Pin 2)
Input supply voltage
LDRV2 (Pin 3)
Linear controller 2 (LCTR2) driver. Connect to the gate of
external N-Channel MOSFET pass transistor to form a
positive linear regulator
LFB2 (Pin 4)
LDO2 feedback input. The feedback set point is 0.8V.
Connect to a resistive divider between the positive linear
regulator output and GND to adjust the output voltage.
COMP (Pin 5)
Switching regulator compensation pin.
FB (Pin 6)
Switching regulator feedback input. The feedback set point
is 0.8V. Connect to a resistive divider between the switching
regulator output and GND to adjust the output voltage.
PGOOD (Pin 7)
Open drain power good indicator. PGOOD is low when
switching regulator output voltage is lower than 10% of its
regulation voltage. Connect a pull high resistor between
PGOOD and switching regulator output for pull high logic
level voltage.
SS/EN (Pin 8)
Soft start input with 8uA sourcing current and IC enable
control.
RT (Pin 9)
Operational frequency setting. Connect a resistor between
RT and GND to set operational frequency. The operational
frequency will nominally run at 200kHz when open.
BOOT (Pin 15)
High side floating driver supply with (+) terminal bootstrap
flying capacitor connection. Voltage swing is from a diode
drop below VINT to VIN + VINT
LFB1 (Pin 16)
LDO1 feedback input. The feed back set point is 0.8V.
Connect to a resistive divider between the positive linear
regulator output and GND to adjust the output voltage.
PHS (Pin 13)
Inductor connection with (-) terminal bootstrap flying
capacitor connection.
UGATE (Pin 14)
High side gate driver. Drives high side N-Channel MOSFET
with a voltage swing between BOOT and PHS
LGATE (Pin 11)
Low side gate driver. Drives low side N-MOSFET with a
voltage swing between VINT and GND
VINT (Pin 12)
Internal 6.0V regulator output. The low side gate driver and
control circuit and external bootstrap diode are powered
by this voltage. Decouple this pin to power ground with a
4.7uF or greater ceramic capacitor close to the VINT pin.
GND (Pin 10)
Ground
The formula between resistor setting and operational
frequency are as follows:
R
RT
=
62
×
10
8
3
F
OSC
- 200
×
10
DS9206-13 April 2011
www.richtek.com
5
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