Richtek RT8812AGQW Schematic [ru]
®
RT8812A
Dual-Pha se PWM Controller with PWM-VID Reference
General Description
The RT8812A is a 2/1 phase synchronous Buck PWM
controller which is optimized for high performa nce gra phic
microprocessor and computer applications. The IC
integrates a Constant-On-T ime (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
Current limit is accomplished through continuous inductorcurrent-sense, while R
accurate channel current balance. Using the method of
current sampling utilizes the best advantages of each
technique.
The RT8812A fe atures external reference input and PWMVID dyna mic output voltage control, in which the feedba ck
voltage is regulated and tracks external input reference
voltage. Other features include adjustable switching
frequency , dynamic pha se number control, internal/external
soft-start, power good indicator, a nd enable function s.
current sensing technique.
DS(ON)
current sensing is used for
DS(ON)
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
Internal Fixed and External Adjustable Soft-Start
Adjustable Current Limit Threshold
Adjustable Switching Frequency
UVP/OVP Protection
Shoot Through Protection and Short Pulse Free
Current Sensing for Current Balance
DS(ON)
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
V
IN
TON
L
G
A
T
E
1
PGOOD
B
O
O
T
2
PSI
UGATE2
PHASE2
VID
L
G
A
T
E
2
EN
GND
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©
RGND
VSNS
DS8812A-04 November 2013 www.richtek.com
V
IN
V
OUT
V
IN
V
GND_SNS
V
OUT_SNS
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 :
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.
Marking Information
0Z= : Product Code
0Z=YM
YMDNN : Date Code
DNN
Function Pin Description
Pin Configurations
(TOP VIEW)
PHASE1
LGATE1
BOOT1
UGATE1
1
2
3
EN
PSI
VID SS
GND
4
REFIN
REFADJ
WQFN-20L 3x3
LGATE2
PVCC
17181920
21
9876
TON
VREF
PHASE2
16
10
RGND
15
BOOT2
14
UGATE2
13
PGOOD
12
VSNS
115
Pin No. Pin Name Pin Function
1 BO OT 1 Boo tstrap Suppl y for PWM 1. T his pin powe rs the high sid e MOS FET driv er.
2 UGATE1
Hig h Side G ate Dri ver of PW M 1. This pi n provi des t he gate driv e for t he conv ert er's
high side MOSFET. Connect this pin to the Gate of high side MOSFET .
3 EN Enable Control Input. Active high input.
Power Sav i ng Interfac e. Wh en t h e vol tag e is pul led below 0. 8V, th e dev ice will o per a te
4 PSI
int o 1 p hase DEM . W hen t he volt age is between 1.2V to 1.8 V, the dev ice wi ll operat e
into 1 phase force CCM . When the voltag e is between 2.4V to 5.5V, the device will
operate into 2 phase force CCM.
5 VID
Programming Output Voltage Control Input. Refer to PWM-VID Dynamic Voltage
Control.
6 REF ADJ Reference Adjustment Outp ut. Refer to PWM-VID Dynami c Voltage Control.
7 REFIN External Reference Input.
8 VREF
9 TON
Reference Voltage Output. This is a high precision voltage ref erence (2V) from the
VRE F pin to RGND pin.
ON -Ti me/Sw itchi ng Freque ncy A djustm ent In put. Con nect a 1 00pF cerami c capac itor
betw een C
and ground is optional for noise immunity enhancement.
TON
10 RGND Negative Remote Sense Input. Connect this pin to the ground of output load.
11 SS
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.
12 VSNS Positive Remote Sense Input. Connect this pin to the positive terminal of output load.
13 PGOOD Po w er Good Indi cator Outpu t. Active high open d rain output.
14 UGATE2
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Hig h Side G ate Dri ver of PW M 2. This pi n provi des t he gate driv e for t he conv ert er's
high side MOSFET. Connect this pin to the Gate of high side MOSFET .
DS8812A-04 November 2013www.richtek.com
Pin No. Pin Name Pin Function
15 BOOT2 Bootstrap Supply for PWM 2. This pin powers the hi gh side MOSFET driver.
Switch Node for PWM2. This pin is return node of the high side driver of PWM 2.
16 PHASE2
Connect this pin to the Source of high side MOSFET together with the Drain of
low side MOSFET and the inductor.
17 LGATE2
18 PVCC
19 LGATE1
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.
Suppl y Voltage Input. Connect this pi n 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.
20 PHASE1
Connect this pin to the Source of high side MOSFET together with the Drain of
low side MOSFET and the inductor.
21 (Exposed Pad) GND
Ground. The Exposed pad should be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
Function Block Diagram
RT8812A
VID
REFADJ
PSI
REFIN
SS
VSNS
RGND
EN
VREF
OV
Threshold
Select
UV
40% REFIN
Soft-Start
& Slew Rate
Control
Enable
Logic
To Power On Reset
Reference
Output Gen.
Mode Select
+
+
-
PWM
CMP
+
-
To Driver Logic
To Power On Reset
Power On Reset
& Central Logic
Control & Protection Logic
TON
Gen 1
TON
Gen 2
Boot-Phase
Detection 1
Boot-Phase
Detection 2
PWM1
Driver
Logic
PWM2
PVCC
PGOOD
BOOT1
UGATE1
PHASE1
LGATE1
BOOT2
UGATE2
PHASE2
LGATE2
TON
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©
VIN
Detection
Current
To Driver LogicZCDPHASE1
To Protection Logic
Balance
Current
Limit
S/H
S/H
GM
GM
+
V
B
+
V
B
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3
RT8812A
Operation
The RT8812A is a 2/1 phase synchronous Buck PWM
controller with integrated drivers which are optimized for
high performance gra phic microprocessor a nd computer
application s. The IC integrates a COT (Constant-On-T ime)
PWM controller with two MOSFET drivers, as well as
output current monitoring and protection functions.
Referring to the function block diagra m of TON Genx, the
synchronous UGA TE 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 consta nt
over the input voltage range a nd output voltage. Another
one-shot sets a minimum off-time.
The RT8812A also features a PWM-VID dyna mic voltage
control circuit driven by the pulse width modulation
method. This circuit reduces the device pin count and
enables a wide dyna mic voltage ra nge.
Soft-Start (SS)
For internal soft-start function, an internal current source
charges an internal capacitor to build the soft-start ra mp
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.
Current Balance
The RT8812A implements internal current balance
mechanism in the current loop. The R T8812A sens es per
phase current a nd compares it with the average current. If
the sensed current of any particular pha se is higher tha n
average current, the on-time of this pha se 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
OV = 2V, or V
> 1.33V, OV = 1.5 x V
REFIN
REFIN
REFIN
≤ 1.33V,
), 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 UGA TE a nd LGATE gate drivers are f orced
low. The controller is latched until PVCC is re-supplied
and exceeds the POR rising threshold voltage or EN is
reset.
When the soft-start is finished, the PGOOD open drain
output will be high impedance.
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RT8812A
Absolute Maximum Ratings (Note 1)
TO N to G ND------------------------------------------------------------------------------------------------------------------ −0.3V to 30V
RGN D t o G ND --------------------------------------------------------------------------------------------------------------- −0.7V to 0.7V
BOOTx to PHASEx-------------------------------------------------------------------------------------------------------- −0.3V to 6V
PHASEx to GND
DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 30V
<20ns ------------------------------------------------------------------------------------------------------------------------- −8V to 36V
UGATEx to PHASEx
DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V
<20ns ------------------------------------------------------------------------------------------------------------------------- −5V to 7.5V
LGA TEx to GND
DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V
<20ns ------------------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V
Other Pins-------------------------------------------------------------------------------------------------------------------- −0.3V to 6V
Power Dissipation, P
D
WQFN-20L 3x3 ------------------------------------------------------------------------------------------------------------- 3.33W
Package Thermal Resistance (Note 2)
WQF N-20L 3x3, θJA-------------------------------------------------------------------------------------------------------- 30°C/W
WQFN-20L 3x3, θJC------------------------------------------------------------------------------------------------------- 7.5°C/W
Lead T e mperature (Soldering, 10 sec.)-------------------------------------------------------------------------------- 26 0°C
Junction T emperature------------------------------------------------------------------------------------------------------ 150°C
Storage T emperature Range --------------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model)----------------------------------------------------------------------------------------------- 2kV
@ T
= 25°C
A
Recommended Operating Conditions (Note 4)
Input V oltage, V
Supply Voltage, V
Junction T emperature Range--------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient T emperature Range--------------------------------------------------------------------------------------------- −40°C to 85°C
----------------------------------------------------------------------------------------------------------- 7V to 26V
IN
---------------------------------------------------------------------------------------------------- 4.5V to 5.5V
PVCC
Electrical Characteristics
(T
= 25°C unless otherwise specified)
A
Parameter Symbol Test Conditions Min Typ Max Unit
PWM Controlle r
PVCC Supply Voltage V
PVCC Supply Current I
PVCC Shu tdown Curre nt I
PVCC POR Threshold 3.8 4.1 4.4 V
POR Hysteresis -- 0.3 -- V
Switching Frequency fSW R
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DS8812A-04 November 2013 www.richtek.com
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4.5 -- 5.5 V
PVCC
SUPPLY
SHDN
EN = 3.3V, Not Switching -- 1.5 2 mA
EN = 0V -- -- 10 A
= 500k (Note 5) 270 300 330 kHz
TON
5
RT8812A
Parameter Symbol Test Conditions Min Typ Max Unit
Minimum On-Time t
M inimu m O ff-Time t
ON(MIN)
OFF(MIN)
-- 70 -- ns
-- 300 -- ns
EN Input Voltage
EN Input Voltage
Logic-High V
Logic-Low V
1.6 -- --
ENH
-- -- 0.8
ENL
V
Mode Decision
PSI High Threshold V
PSI Intermediate Threshold V
PSI Low Threshold V
High-Level V
VID Input Voltage
Low-Level V
Enables Two Phases with FCCM 2.4 -- -- V
PSIH
Enables One Phases with FCCM 1.2 -- 1.8 V
PSIM
Enables One Phases with DEM -- -- 0.8 V
PSIL
2 -- --
VIDH
-- -- 1
VIDL
V
Protection Function
Zero Current Crossing
Threshold
Current Limit Setting Current I
Current Limit Setting Current
Temperature Coefficient
Current Limit Threshold R
Absolute Over Voltage
Protection Threshold
Relative Over Voltage
Protection Threshold
8 -- 8 mV
9 10 11 A
OCS ET
I
OCS ET_TC
V
OVP, Ab sol u te
V
OVP, Relat i ve
-- 6300 -- ppm/C
= 10k -- 60 -- mV
OCS ET
V
V
1. 33V 1.9 2 2.1 V
REFIN
> 1.33V 145 150 155 %
REFIN
OV Fault Delay FB forced above OV threshold -- 5 -- s
Rel ative Under V oltage
Protection Threshold
UVP 35 40 45 %
V
UVP
UV Fault Delay FB forced above UV threshold -- 3 -- s
Thermal Shutdown Threshold TSD -- 150 -- C
PGOOD Blanking Time
(Internal)
From EN = high to PGOOD = high
with VSNS within regulation point
-- 2.5 -- ms
From first UGAT E t o VSNS
VSNS Soft-Start (Internal)
regu lati on point, V
REFIN
= 1V and
-- 0.7 -- ms
VSNS ini tial = 0V
Soft-Start Current Source ISS -- 5 -- A
Er ror Amp l i f ier
VSNS Error Comparator
Threshold (Valley)
V
= 1V 17.5 12.5 7.5 mV
REFIN
Reference
Reference Voltage V
VREF
Sourcing Current = 1mA, VID no
Switching
1.98 2 2.02 V
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DS8812A-04 November 2013www.richtek.com
Parameter Symbol Test Conditions Min Typ Max Unit
Driver On-Resistance
RT8812A
UGATE Dri ver Source R
UGATE Dri ver Sink R
LGATE Driver Source R
LGATE Driver Sink R
UGATEsr
UGATEsk
LGATEsr
LGATEsk
Dead-Time
Internal Boost Charging
Switch On-Resistance
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2. θ
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Not production tested. Test condition is V
is measured at T
JA
measured at the exposed pad of the package.
R
BOOT
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
A
BOOTx PHAS Ex Force d to 5V -- 2 4
BOOTx PHASEx Forced to 5V -- 1 2
LG ATEx, Hi gh State -- 1.5 3
LGATEx, Low State -- 0.7 1.5
From LGATE Falling to UGATE
Rising
From UGATE Falling to LGATE
Rising
PVCC to BOOTx, I
= 8V, V
IN
OUT
BOOT
= 1V, I
= 10mA -- 40 80
= 20A using application circuit.
OUT
-- 30 --
-- 20 --
ns
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