®
RT8812A
Dual-Phase PWM Controller with PWM-VID Reference
General Description
The RT8812A is a 2/1 phase synchronous Buck PWM
controller which is optimized for high performance graphic
microprocessor and computer applications. The IC
integrates a Constant-On-Time (COT) PWM controller, two
MOSFET drivers with internal bootstrap diodes, as well
as channel current balance and protection functions
including Over Voltage Protection (OVP), Under Voltage
Protection (UVP), current limit, and thermal shutdown into
the WQFN-20L 3x3 package.
The RT8812A adopts R
DS(ON)
current sensing technique.
Current limit is accomplished through continuous inductor-
current-sense, while R
DS(ON)
current sensing is used for
accurate channel current balance. Using the method of
current sampling utilizes the best advantages of each
technique.
The RT8812A features external reference input and PWM-
VID dynamic output voltage control, in which the feedback
voltage is regulated and tracks external input reference
voltage. Other features include adjustable switching
frequency, dynamic phase number control, internal/external
soft-start, power good indicator, and enable functions.
Features
Dual-Phase PWM Controller
Two Embedded MOSFET Drivers and Embedded
Switching Boot Diode
External Reference Input Control
PWM-VID Dynamic Voltage Control
Dynamic Phase Number Control
Lossless R
DS(ON)
Current Sensing for Current Balance
Internal Fixed and External Adjustable Soft-Start
Adjustable Current Limit Threshold
Adjustable Switching Frequency
UVP/OVP Protection
Shoot Through Protection and Short Pulse Free
Technology
Support an Ultra-Low Output Voltage as Standby
Voltage
Thermal Shutdown
Power Good Indicator
RoHS Compliant and Halogen Free
Applications
CPU/GPU Core Power Supply
Notebook PC Memory Power Supply
Chipset/RAM Power Supply
Generic DC/DC Power Regulator
Simplified Application Circuit
RT8812A
V
PVCC
PVCC
BOOT1
UGATE1
PHASE1
LGATE1
V
IN
V
OUT
V
IN
TON
PGOOD
PSI
VID
EN
GND
BOOT2
UGATE2
V
IN
PHASE2
LGATE2
RGND
VSNS
V
GND_SNS
V
OUT_SNS
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8812A-04 November 2013
www.richtek.com
1
RT8812A
Ordering Information
RT8812A
Package Type
QW : WQFN-20L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Pin Configurations
(TOP VIEW)
PHASE1
LGATE1
PVCC
LGATE2
PHASE2
20 19 18 17 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.
BOOT1
UGATE1
EN
PSI
VID
1
2
3
4
5
6
7
8
9 10
15
14
GND
21
13
12
11
BOOT2
UGATE2
PGOOD
VSNS
SS
½
Marking Information
0Z= : Product Code
WQFN-20L 3x3
0Z=YM
DNN
YMDNN : Date Code
Function Pin Description
Pin No.
1
2
3
4
Pin Name
BOOT1
UGATE1
EN
PSI
Pin Function
Bootstrap Supply for PWM 1. This pin powers the high side MOSFET driver.
High Side Gate Driver of PWM 1. This pin provides the gate drive for the converter's
high side MOSFET. Connect this pin to the Gate of high side MOSFET.
Enable Control Input. Active high input.
Power Saving Interface. When the voltage is pulled below 0.8V, the device will operate
into 1 phase DEM. When the voltage is between 1.2V to 1.8V, the device will operate
into 1 phase force CCM. When the voltage is between 2.4V to 5.5V, the device will
operate into 2 phase force CCM.
Programming Output Voltage Control Input. Refer to PWM-VID Dynamic Voltage
Control.
Reference Adjustment Output. Refer to PWM-VID Dynamic Voltage Control.
External Reference Input.
Reference Voltage Output. This is a high precision voltage reference (2V) from the
VREF pin to RGND pin.
ON-Time/Switching Frequency Adjustment Input. Connect a 100pF ceramic capacitor
between C
TON
and ground is optional for noise immunity enhancement.
Negative Remote Sense Input. Connect this pin to the ground of output load.
Soft-Start Time Setting. Connect an external capacitor to adjust soft-start time.
When the external capacitor is removed, the internal soft-start function will be chose.
Positive Remote Sense Input. Connect this pin to the positive terminal of output load.
Power Good Indicator Output. Active high open drain output.
High Side Gate Driver of PWM 2. This pin provides the gate drive for the converter's
high side MOSFET. Connect this pin to the Gate of high side MOSFET.
is a registered trademark of Richtek Technology Corporation.
5
6
7
8
9
10
11
12
13
14
VID
REFADJ
REFIN
VREF
TON
RGND
SS
VSNS
PGOOD
UGATE2
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
REFADJ
REFIN
VREF
TON
RGND
DS8812A-04 November 2013
RT8812A
Pin No.
15
16
Pin Name
BOOT2
PHASE2
Pin Function
Bootstrap Supply for PWM 2. This pin powers the high side MOSFET driver.
Switch Node for PWM2. This pin is return node of the high side driver of PWM 2.
Connect this pin to the Source of high side MOSFET together with the Drain of
low side MOSFET and the inductor.
Low Side Gate Driver of PWM 2. This pin provides the gate drive for the
converter's low side MOSFET. Connect this pin to the Gate of low side MOSFET.
Supply Voltage Input. Connect this pin to a 5V bias supply. Place a high quality
bypass capacitor from this pin to GND.
Low Side Gate Driver of PWM 1. This pin provides the gate drive for the
converter's low side MOSFET. Connect this pin to the Gate of low side MOSFET.
Switch Node for PWM1. This pin is return node of the high side driver of PWM 1.
Connect this pin to the Source of high side MOSFET together with the Drain of
low side MOSFET and the inductor.
Ground. The Exposed pad should be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
17
18
19
LGATE2
PVCC
LGATE1
20
PHASE1
21 (Exposed Pad) GND
Function Block Diagram
VREF
Reference
Output Gen.
PVCC
Mode Select
OV
Threshold
Select
UV
40% REFIN
+
-
-
+
VID
REFADJ
PSI
REFIN
Power On Reset
& Central Logic
PGOOD
Control & Protection Logic
Boot-Phase
Detection 1
Boot-Phase
Detection 2
TON
Gen 1
PWM1
LGATE1
TON
Gen 2
PWM2
Driver
Logic
BOOT2
UGATE2
PHASE2
LGATE2
BOOT1
UGATE1
PHASE1
SS
VSNS
RGND
EN
Soft-Start
& Slew Rate
Control
PWM
CMP
+
-
Enable
Logic
To Driver Logic
To Power On Reset
To Power On Reset
TON
V
IN
Detection
Current
Balance
PHASE1
ZCD
To Driver Logic
To Protection Logic
Current
Limit
S/H
-
GM
+
-
GM
+
S/H
V
B
V
B
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8812A-04 November 2013
www.richtek.com
3
RT8812A
Operation
The RT8812A is a 2/1 phase synchronous Buck PWM
controller with integrated drivers which are optimized for
high performance graphic microprocessor and computer
applications. The IC integrates a COT (Constant-On-Time)
PWM controller with two MOSFET drivers, as well as
output current monitoring and protection functions.
Referring to the function block diagram of TON Genx, the
synchronous UGATE driver is turned on at the beginning
of each cycle. After the internal one-shot timer expires,
the UGATE driver will be turned off. The pulse width of
this one-shot is determined by the converter's input voltage
and the output voltage to keep the frequency fairly constant
over the input voltage range and output voltage. Another
one-shot sets a minimum off-time.
The RT8812A also features a PWM-VID dynamic voltage
control circuit driven by the pulse width modulation
method. This circuit reduces the device pin count and
enables a wide dynamic voltage range.
Soft-Start (SS)
For internal soft-start function, an internal current source
charges an internal capacitor to build the soft-start ramp
voltage. The output voltage will track the internal ramp
voltage during soft-start interval. For external soft-start
function, an additional capacitor connected from SS pin
to the GND will be charged by a current source and
determines the soft-start time.
PGOOD
The power good output is an open drain architecture.
When the soft-start is finished, the PGOOD open drain
output will be high impedance.
Current Balance
The RT8812A implements internal current balance
mechanism in the current loop. The RT8812A senses per
phase current and compares it with the average current. If
the sensed current of any particular phase is higher than
average current, the on-time of this phase will be adjusted
to be shorter.
Current Limit
The current limit circuit employs a unique
“valley”
current
sensing algorithm. If the magnitude of the current sense
signal at PHASE is above the current limit threshold, the
PWM is not allowed to initiate a new cycle. Thus, the
current to the load exceeds average output inductor
current, the output voltage falls and eventually crosses
the under voltage protection threshold, inducing IC
shutdown.
Over Voltage Protection (OVP) & Under Voltage
Protection (UVP)
The output voltage is continuously monitored for over
voltage and under voltage protection. When the output
voltage exceeds its set voltage threshold (If V
REFIN
≤
1.33V,
OV = 2V, or V
REFIN
> 1.33V, OV = 1.5 x V
REFIN
), UGATE
goes low and LGATE is forced high; when it is less than
40% of its set voltage, under voltage protection is triggered
and then both UGATE and LGATE gate drivers are forced
low. The controller is latched until PVCC is re-supplied
and exceeds the POR rising threshold voltage or EN is
reset.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8812A-04 November 2013
RT8812A
Absolute Maximum Ratings
(Note 1)
−0.3V
to 30V
−0.7V
to 0.7V
−0.3V
to 6V
−0.3V
to 30V
−8V
to 36V
TON to GND ------------------------------------------------------------------------------------------------------------------
RGND to GND ---------------------------------------------------------------------------------------------------------------
BOOTx to PHASEx --------------------------------------------------------------------------------------------------------
PHASEx to GND
DC ------------------------------------------------------------------------------------------------------------------------------
<20ns -------------------------------------------------------------------------------------------------------------------------
UGATEx to PHASEx
DC ------------------------------------------------------------------------------------------------------------------------------
−0.3V
to 6V
<20ns -------------------------------------------------------------------------------------------------------------------------
−5V
to 7.5V
LGATEx to GND
DC ------------------------------------------------------------------------------------------------------------------------------
−0.3V
to 6V
<20ns -------------------------------------------------------------------------------------------------------------------------
−2.5V
to 7.5V
Other Pins --------------------------------------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
WQFN-20L 3x3 ------------------------------------------------------------------------------------------------------------- 3.33W
Package Thermal Resistance (Note 2)
WQFN-20L 3x3,
θ
JA
--------------------------------------------------------------------------------------------------------
WQFN-20L 3x3,
θ
JC
-------------------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------
Junction Temperature ------------------------------------------------------------------------------------------------------
Storage Temperature Range ---------------------------------------------------------------------------------------------
ESD Susceptibility (Note 3)
HBM (Human Body Model) -----------------------------------------------------------------------------------------------
(Note 4)
7V to 26V
4.5V to 5.5V
−40°C
to 125°C
−40°C
to 85°C
30°C/W
7.5°C/W
260°C
150°C
−65°C
to 150°C
2kV
Recommended Operating Conditions
Input Voltage, V
IN
-----------------------------------------------------------------------------------------------------------
Supply Voltage, V
PVCC
----------------------------------------------------------------------------------------------------
Junction Temperature Range ---------------------------------------------------------------------------------------------
Ambient Temperature Range ---------------------------------------------------------------------------------------------
Electrical Characteristics
(T
A
= 25°C unless otherwise specified)
Parameter
PWM Controller
PVCC Supply Voltage
PVCC Supply Current
PVCC Shutdown Current
PVCC POR Threshold
POR Hysteresis
Switching Frequency
Symbol
V
PVCC
I
SUPPLY
I
SHDN
Test Conditions
Min
4.5
Typ
--
1.5
--
4.1
0.3
300
Max
5.5
2
10
4.4
--
330
Unit
V
mA
A
V
V
kHz
EN = 3.3V, Not Switching
EN = 0V
--
--
3.8
--
f
SW
R
TON
= 500k
(Note 5)
270
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8812A-04 November 2013
www.richtek.com
5
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