RT8809 - Richtek

®
RT8809
Dual-Phase PWM Controller for GPU Core Power Supply
General Description
Features
The RT8809 is a dual-phase synchronous Buck PWM
controller with integrated drivers which are optimized for
high-performance graphic microprocessor and computer
applications. The IC integrates a G-NAVP TM PWM
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Dual-Phase PWM Controller
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Two Embedded MOSFET Drivers and Embedded
Switching Boot Diode
Green-NAVP TM (Green Native Adaptive Voltage
Positioning) Topology
Dynamic Auto-Phase Control with Adjustable
Threshold
Cross-talk Jitter Suspend (CJSTM)
Remote GND Detection for High Accuracy
Automatic Diode Emulation Mode/or Ultrasonic
Mode at Light Load
Lossless RDS(ON) Current Sensing for Current Balance
Lossless DCR Current Sensing for AVP & OCP
Reference Voltage Output with 1% Accuracy
External Reference Input with Soft-Start (RISS)
Embedded One-Bit VID Control
Adjustable OCP Threshold
Adjustable Switching Frequency
Reference-Tracking UVP/OVP Protection
Shoot Through Protection and Short Pulse Free
Technology
RoHS Compliant and Halogen Free
controller, two 12V MOSFET drivers with internal bootstrap
diodes, as well as output current monitoring and protection
functions into the WQFN-24L 4x4 package. The RT8809
adopts DCR and RDS(ON) current sensing. Load line voltage
positioning (droop) and over-current protection are
accomplished through continuous inductor DCR current
sensing, while RDS(ON) current sensing is used for accurate
channel-current balance. Using both methods of current
sampling utilizes the best advantages of each technique.
The RT8809 also features a one-bit VID control operation
in which the feedback voltage is regulated and tracks
external input reference voltage. Other features include
output current indication, adjustable operating frequency,
power good indication, external compensation, and
enable/shutdown functions.
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Simplified Application Circuit
VIN
VDD
C8
VCC
RT8809
BOOT1
R18
R22
R16
VIN
EN/MODE
R17
BOOT2
PS
RMPSET
LGATE2
TON
C10
VIN
Q3
UGATE2
L2
Q4
R11
C3
EN/MSEL
PGND
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
R10
C14
PHASE2
R20
Q2
LGATE1
OCP
VOUT
L1
PHASE1
VSET
R21
C6
Q1
UGATE1
VREF
VRTN
C9
CSP
CSN
FB
VRTN
R14
R15
is a registered trademark of Richtek Technology Corporation.
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1
RT8809
Applications
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Marking Information
Middle to High End GPU Core Power
High End Desktop PC Memory Core Power
Low Voltage, High Current DC/DC Converter
Voltage Regulator Modules
Ordering Information
RT8809
DQ=: Product Code
DQ=YM
DNN
YMDNN : Date Code
Pin Configurations
(TOP VIEW)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
24 23 22 21 20 19
VSET
VREF
EN/MSEL
RMPSET
COMP
FB
1
18
2
17
3
15
25
5
14
13
6
7
Suitable for use in SnPb or Pb-free soldering processes.
16
PGND
4
8
VCC
VDD
LGATE1
PHASE1
UGATE1
BOOT1
9 10 11 12
VRTN
TON
OCP
CSN
CSP
PS
`
RSET
VID
BOOT2
UGATE2
PHASE2
LGATE2
Package Type
QW : WQFN-24L 4x4 (W-Type)
(Exposed Pad-Option 2)
WQFN-24L 4x4
Functional Pin Description
Pin No.
Pin Name
Pin Function
Output Voltage Setting. Connect a voltage divider from VREF to VSET to set the output
voltage.
1
VSET
2
VREF
3
EN/MSEL
4
RMPSET
5
COMP
Compensation Node. This pin is the output node of the error amplifier.
6
FB
Feedback Voltage Input. This pin is the negative input node of the error amplifier.
7
VRTN
Remote Differential Feedback, Invert Input. This pin is the negative node of the
differential remote voltage sensing.
8
TON
9
OCP
10
CSN
On-Time (Switching Frequency) Setting. Connect a resistor (R TON) from TON to VIN to
set the switching frequency. The value of RTON must be set equal to RRMP.
OCP Level Setting. Connect a resistor from OCP to GND to set the current limit
threshold.
This pin is negative input of current sensing.
11
CSP
This pin is positive input of current sensing.
12
PS
Dynamic Phase Control Input. Connect a resistor from PS to GND to set the auto down
phase threshold.
Reference Voltage Output (2V). The RT8809 generates a 2V reference voltage from
VREF to VRTN.
Enable Control Input and Mode Selection. This pin is a tri-state input. Pull up this pin to
exceed than 4V, controller operation into DEM mode. Pull up this pin to between 1.2V
to 3V, controller operation into ASM mode. Pull down this pin to GND, controller will
shutdown.
Internal Ramp Slew-Rate Setting. Connect a resistor (RRMP) from RMPSET to GND to
the ramp slew rate. The value of RRMP must be set equal to RTON.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8809-00 May 2013
RT8809
Pin No.
Pin Name
Pin Function
13
BOOT1
Supply for High-Side Gate Driver of Phase 1.
14
UGATE1
High-Side Gate Driver of PHASE1. This pin provides the gate drive for the
converter's high-side MOSFET. Connect this pin to the high-side MOSFET
gate.
15
PHASE1
This pin is return node of the high-side driver of PHASE1. Connect this pin to
high-side MOSFET Source together with the low-side MOSFET Drain and the
inductor.
16
LGATE1
Low-Side Gate Driver of PHASE1. This pin provides the gate drive for the
converter's low-side MOSFET. Connect this pin to the low-side MOSFET
gate.
17
VDD
Regulator Power for Internal Circuit. The regulated voltage provides power
supply for all low-voltage circuits.
18
VCC
Supply Voltage Input. Connect this pin to GND by a ceramic cap larger than
1μF.
19
LGATE2
Low-Side Gate Driver of PHASE2. This pin provides the gate drive for the
converter's low-side MOSFET. Connect this pin to the low-side MOSFET
gate.
20
PHASE2
This pin is return node of the high-side driver of PHASE2. Connect this pin to
high-side MOSFET Source together with the low-side MOSFET Drain and the
inductor.
21
UGATE2
High-Side Gate Driver of PHASE2. This pin provides the gate drive for the
converter's high-side MOSFET. Connect this pin to the high-side MOSFET
gate.
22
BOOT2
Bootstrap Supply for High-Side Gate Driver of Phase 2. This pin powers the
high-side MOSFET driver.
23
VID
Programming Output Voltage Control. When VID pin is logic high, internal
N-MOSFET that connected to RSET pin is turn on.
24
RSET
Output Voltage Setting. Connect a resistor from RSET pin to VSET pin, the
output voltage can be switched two level by driving VID pin.
25 (Exposed Pad)
PGND
Power Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
is a registered trademark of Richtek Technology Corporation.
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3
RT8809
Function Block Diagram
VID
VREF
RSET
VCC
Reference
Output Gen.
PGOOD Up
Trip Point
Internal
Regulator&BG
+
-
PGOOD Down
Trip Point
VDD
Power On Reset
& Central Logic
+
VSET
UV Trip Point
+
Control & Protection Logic
-
OV Trip Point
+
-
Boot-Phase
Detection 1
Ramp
Gen
RMPSET
VRTN
Soft Start &
Slew Rate
Control
FB
EN/MSEL
+
+
ERROR
AMP
COMP
EN/Mode
Select
Boot-Phase
Detection 2
VSETA
+
+
+
+
+
LPF
+
+
BOOT1
UGATE1
PHASE1
TON
Gen 1
PWM
CMP
PWM1
-
To Power
on Reset
To driver Logic
ZCD
To Power on
Reset
PHASE1 To driver Logic
LGATE1
Driver
Logic
TON
Gen 2
PWM2
LGATE2
PGND
VIN
Detection
TON
S/H
GM
+
S/H
GM
+
Current
Balance
PS
CSP
CSN
OCP
Phase
shedding
+
-
5
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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4
BOOT2
UGATE2
PHASE2
Isum
OCP
1/2
+
To Protection Logic
is a registered trademark of Richtek Technology Corporation.
DS8809-00 May 2013
RT8809
Operation
The RT8809 integrates a PWM controller, two 12V
MOSFET drivers with internal bootstrap diodes, as well
as output current monitoring and protection functions.
Power On Reset
The Power On Reset (POR) circuit monitors the supply
voltage of the controller (VCC). When VCC exceeds the
POR rising threshold, the controller will be enabled. If
VCC falls below the POR falling threshold during normal
operation, all MOSFETs stop switching. There is a
hysteresis between the POR rising threshold and falling
threshold to prevent noise mis-trigger.
Soft-Start
Current Balance
The RT8809 implements internal current balance
mechanism in the current loop. The RT8809 senses each
phase current signal 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.
OCP
Once the sensed total current exceeds the current limit
threshold, the driver will be forced to turn off the gate drivers
for high side power MOSFETs. Until the OCP situation is
removed.
An internal soft-start function is used to prevent large
inrush current while converter is powered-up. The FB
voltage will track the internal soft-start voltage during softstart interval. During the soft-start period, the controller
will operate in dual-phase mode to ensure enough charge
for output loads.
Over-Voltage Protection
EN/Mode Select
Under-Voltage Protection
The RT8809 supports DEM (Diode Emulation Mode) and
ASM (Audio Skipping Mode) operation which can be
enabled by EN/MSEL pin. When the EN/MSEL pin is
pulled up above 4.2V, the controller will operate in DEM
and reduce the switching frequency at light load conditions
for saving power loss. If the EN/MSEL voltage is between
1.2V and 3V, the controller will operate in ASM. In ASM
operation, the minimum switching frequency is limited to
30kHz to avoid acoustic noises. If the pin is pulled to
GND, the RT8809 will be shut down.
The voltage on CSN pin is also monitored for Under-Voltage
Protection (UVP). If the output voltage is lower than the
UVP threshold, the controller will turn off both high side
and low side MOSFETs. When the UVP is triggered, the
RT8809 will enter hiccup mode and continuously try to
restart until the UVP situation is removed.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
The RT8809 monitors the output voltage via the CSN pin
for Over-Voltage Protection (OVP). Once the output voltage
exceeds the OVP threshold, the controller will turn off
high side MOSFETs and turn on low side MOSFETs to
protect the load until the OVP situation is removed.
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5
RT8809
Absolute Maximum Ratings
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(Note 1)
VDD, VSEN, COMP, VSET, VREF, EN/MSEL, PS, OCP, CSN,
CSP, RSET, VID, RMPSET to PGND ---------------------------------------------------------VCC, TON to PGND ------------------------------------------------------------------------------VRTN to PGND -------------------------------------------------------------------------------------BOOTx to PHASEx -------------------------------------------------------------------------------PHASE to PGND
DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------LGATEx to PGND
DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------UGATEx to PHASEx
DC -----------------------------------------------------------------------------------------------------<20ns ------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WQFN-24L 4x4 ------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WQFN-24L 4x4, θJA -------------------------------------------------------------------------------WQFN-24L 4x4, θJC ------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) -----------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 6V
−0.3V to 15V
−0.3V to 0.3V
−0.3V to 15V
−3V to 15V
−5V to 30V
−0.3V to PVCC+ 0.3V
−5V to (VCC + 5V)
−0.3V to BOOTx − PHASEx
−5V to (BOOTx − PHASEx + 5V)
3.57W
28°C/W
7.1°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Voltage, VCC ------------------------------------------------------------------------------- 4.5V to 13.2V
Junction Temperature Range --------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC = 12V, No Load, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
4.5
12
13.2
V
Supply Input
Supply Voltage
VCC
Supply Current
IVCC + IPVCC EN = 3.3V, Not Switching
--
4
--
mA
Shutdown Current
ICC + IPVCC
EN = 0V
--
--
500
μA
(No Load, Active Mode )
--
2
--
Accuracy
−1%
--
1%
VSET pin (this max. voltage will affect
VCOMP max.)
0.5
--
2
Reference
Reference Output
VREF
Reference Input Range
VSET
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V
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DS8809-00 May 2013
RT8809
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
--
2
--
ms
--
300
--
μs
--
0.5
--
mV/μs
−8
--
8
mV
RL = 47kΩ
--
80
--
dB
CLOAD = 5pF
CLOAD = 10pF (Gain = −4,
Rf = 47k, VOUT = 0.5V to 3V)
RL = 47kΩ
(max. depend on VSET max.)
VCOMP = 2V
--
10
--
MHz
--
5
--
V/μs
0.5
--
3
V
--
250
--
μA
Start Up Delay
Initial Soft-Start time
Reference Change Delay
Time
Internal VID Change Slew
Rate
Error Amplifier
Input Offset Voltage
tb
Initially, VOUT = 0.1V to 1.2V
tc
td
VOUT = 1.2V to Set Voltage
VOSEA
DC Gain
Gain-Bandwidth Product
GBW
Slew Rate
SR
Output Voltage Range
VCOMP
MAX Source Current
IOUTEA
Current Sense Amplifier (for Droop and OCP and Phase Shedding)
Input Offset Voltage
VOSCS
−1
--
1
mV
Impedance at Neg. Input
RISEN_N
1
--
--
MΩ
Impedance at Pos Input
RISEN
1
--
--
MΩ
--
5
--
V/V
−50
--
100
mV
DC Gain
Input range
VISEN_in
TON Setting
TON Pin Output Voltage
V TON
IRTON = 62μA
--
VSET
--
V
ON-Time Setting
T ON
IRTON = 62μA
--
350
--
ns
TON Input Current Range
IRTON
25
--
280
μA
--
3.8
--
V
2.1
--
--
V
Protection
Under Voltage Lockout
Threshold
VUVLO
Falling edge
Absolute Over-Voltage
Protection Threshold
VOVABS
Respect to V OUT
Over-Voltage Protection
Threshold
VREL_OV
Respect to V OUT(MAX)
--
135%
--
V
Under-Voltage Protection
Threshold
VUV
Measured at VSENS with respect to
unloaded output voltage (UOV)
--
50%
--
mV
Negative-Voltage Protection
VNV
Threshold
−50
--
--
mV
Current Source by OCP Pin IOCP
7.2
8
8.8
μA
--
--
0.5
V
ASM Mode
1.2
--
3
DEM Mode
4
--
--
−1
--
+5
Logic Inputs
EN Input Voltage
EN Pin Mode Select
Voltage
VIL
Low Level (SD) (Hysteresis)
Leakage Current of EN
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
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μA
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7
RT8809
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
--
8
--
μA
--
500
--
ns
Auto Phase Control
Current Source by PSI
IPS
Maximum Duty Cycle
UGATE Min. Off-Time
Gate Driver
--
1.2
--
A
--
2
--
Ω
ILGATEsr
VBOOTx − VPHASEx = 6V
VUGATEx − V PHASEx = 0.1V,
IUGATEx = 50mA
VCC − VLGATEx = 6V
--
1.2
--
A
RLGATEsk
VLGATEx = 0.1V, ILGATEx = 50mA
--
1
--
Ω
RBOOT
PVCC to BOOTx
--
20
--
Ω
Upper Driver Source
IUGATEsr
Upper Driver Sink
RUGATEsk
Lower Driver Source
Lower Driver Sink
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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT8809
Typical Application Circuit
VIN
12V
RT8809
17 VDD
C8
10µF
C4 Optional
C5
Optional
R18
11k
VRTN
R19
15k
BOOT1 13
UGATE1 14
1
PHASE1 15
VSET
R4
Optional
R22 56k
VIN
2 VREF
24 RSET
R21 43k
9
OCP
12 PS
R16 160k
4 RMPSET
R20 160k
8 TON
R17 100
EN/MODE
VCC 18
3 EN/MSEL
VID 23
BOOT2 22
UGATE2 21
PHASE2 20
PGND
FB
6
VRTN 7
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
C9
0.1µF
Q1
L1
R5 0
Q2
GPIO
R9 0
C14
0.1µF
Q3
R7
NC
C12
NC
VIN
C13
10µF
/16V x 5
R8 0
Q4
LGATE2 19
CSP 11
CSN 10
C6
10µF/16V x 5
R6 0
LGATE1 16
COMP 5
25 (Exposed pad)
R3 1
C7
10µF
R12
NC
C15
NC
0.36µH
/0.8m
R10
9.1k
VOUT
1.1V
C10
820µF
/2.5V x 4
C11
10µF
/6.3V x 10
L2
0.36µH/0.8m
R11
9.1k
R13 NC
C3 0.1µF
C2
1.5nF
C1
2.2nF
R2
R1
3.9k
2k
R14
100
R15
100
VCC_SNS
VSS_SNS
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9
RT8809
Typical Operating Characteristics
Efficiency vs. Load Current
Efficiency vs. Load Current
100
100
90
90
80
80
Phase 2 Active
Efficiency (%)
Efficiency (%)
70
60
50
40
30
20
70
60
50
40
30
20
10
10
VIN = VCC = 12V, VOUT = 1.1V
0
0
5
10
15 20 25 30 35 40
VIN = VCC = 12V, VOUT = 1.1V
0
0.01
45 50 55 60
0.1
Load Current (A)
TON vs. Temperature
10
VREF vs. Temperature
360
2.04
355
2.03
350
2.02
VREF (V)
345
TON (ns)
1
Load Current (A)
340
335
330
2.01
2.00
1.99
1.98
325
1.97
320
VIN = VCC = 12V, No Load
315
VIN = VCC = 12V, No Load
1.96
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
Temperature (°C)
Temperature (°C)
Inductor Current vs. Output Current
Power On from EN
100
125
35
VIN = VCC = 12V, IOUT = 50A
Inductor Current (A)
30
VEN
(10V/Div)
25
Phase 1
Phase 2
20
VOUT
(1V/Div)
15
10
UGATE1
(50V/Div)
5
UGATE2
(50V/Div)
VIN = VCC = 12V
0
20
25
30
35
40
45
50
55
60
Time (1ms/Div)
Output Current (A)
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RT8809
Power On from VCC
Power Off from EN
VIN = VCC = 12V, IOUT = 50A
VEN
(10V/Div)
VIN = VCC = 12V, IOUT = 50A
V CC
(10V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
Time (1ms/Div)
Time (1ms/Div)
Power Off from VCC
Dynamic Output Voltage Control
VIN = VCC = 12V, IOUT = 50A
V CC
(10V/Div)
VSET
(1V/Div)
VOUT
(1V/Div)
VOUT
(500mV/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
VIN = VCC = 12V, VSET = 0.8V to 1.1V, IOUT = 25A
Time (1ms/Div)
Time (400μs/Div)
Dynamic Output Voltage Control
Load Transient Response
VIN = VCC = 12V, RLL = 1.5mΩ
VSET
(1V/Div)
VOUT
(500mV/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
VOUT
(500mV/Div)
IOUT
(50A/Div)
UGATE1
(50V/Div)
VIN = VCC = 12V, VSET = 1.1V to 0.8V, IOUT = 25A
Time (400μs/Div)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
UGATE2
(50V/Div)
Time (10μs/Div)
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11
RT8809
OVP
Load Transient Response
VIN = VCC = 12V, IOUT = 25A
VIN = VCC = 12V, RLL = 1.5mΩ
VOUT
(500mV/Div)
VOUT
(1V/Div)
IOUT
(50A/Div)
UGATE1
(20V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
LGATE1
(10V/Div)
Time (10μs/Div)
Time (20μs/Div)
UVP
Short Circuit
VIN = VCC = 12V
VIN = VCC = 12V, IOUT = 50A
VOUT
(1V/Div)
VOUT
(1V/Div)
UGATE1
(20V/Div)
IL1
(20A/Div)
LGATE1
(10V/Div)
IL2
(20A/Div)
Time (10μs/Div)
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Time (10ms/Div)
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RT8809
Application Information
The RT8809 is a dual-phase synchronous Buck PWM
controller with integrated drivers which is optimized for
high-performance graphic microprocessor and computer
applications. A COT (Constant-On-Time) PWM controller
and two 12V MOSFET drivers with internal bootstrap
diodes are integrated so that the external circuit can be
easily designed and the component count can be reduced.
The RT8809 adopts G-NAVPTM (Green-Native Adaptive
Voltage Positioning), which is Richtek's proprietary
topology derived from finite DC gain compensator with
current mode control. The load line can be easily
programmed by setting the DC gain of the error amplifier.
The IC also adopts lossless DCR and RDS(ON) current
sensing. Voltage positioning, dynamic phase control and
current limit are accomplished through continuous inductor
DCR current sensing, while RDS(ON) current sensing is
used for accurate channel-current balance.
Dynamic mode transition function with various operating
states, which include dual-phase, single phase, diode
emulation and audio skipping modes is supported. These
different operating states make the system efficiency as
high as possible.
A one-bit VID control operation in which the feedback
voltage is regulated and tracks external input reference
voltage is provided. The RT8809 also features complete
fault protection functions including over-voltage, undervoltage and current limit.
DEM/ASM Mode Selection
DEM (Diode Emulation Mode) and ASM (Audio Skipping
Mode) operation can be enabled by driving the tri-state
EN/MSEL pin to a logic high level. The RT8809 can switch
operation into DEM when EN/MSEL pin is pulled up to
above 4V. In DEM operation, the RT8809 automatically
reduces the operation frequency at light-load conditions
for saving power loss. If EN/MSEL is pulled between 1.2V
to 3V, the controller will switch operation into ASM. In
ASM operation, the minimum switching frequency is
limited to 30kHz to avoid the acoustic noise. Finally, if
the pin is pulled to GND, the RT8809 will shutdown.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
Power On Reset
The POR (power on reset) circuit monitors the supply
voltage of the controller (VCC). When VCC exceeds the
POR rising threshold, the controller will be enabled. After
the soft-start, the output voltage will first boot to around
1V, and then change to the set level. If VCC falls below the
POR falling threshold during normal operation, all
MOSFETs stop switching and the controller resets. The
POR rising and falling threshold has a hysteresis to prevent
noise mis-trigger.
Soft-Start
The RT8809 provides soft-start function. The soft-start
function is used to prevent large inrush current while
converter is being powered-up. An internal current source
charges the is internal soft-start capacitor such that the
internal soft-start voltage ramps up in a monotone to a
VBOOT voltage (1V). The FB voltage will track the internal
soft-start voltage during soft-start interval. Therefore, the
duty cycle of the UGATE signal at power up as well as
the input current limited. During the soft-start period, the
controller will be in dual-phase operation by default to
ensure enough charge during start-up.
One-Bit VID and Dynamic Output Voltage Control
The output voltage is determined by the applied voltage
on the VSET pin. The RT8809 generates a 2V reference
voltage from VREF to VRTN. As shown in Figure 1,
connecting a resistor divider from the VREF pin to the
VSET pin can set the output voltage according to the
equation below :
VOUT = 2V × ⎛⎜ R2 ⎞⎟
⎝ R1 + R2 ⎠
The RT8809 also features a one-bit VID control through
an internal N-MOSFET also shown in Figure 1. By connect
a resistor (R3) from RSET pin to VSET pin, the output
voltage can be switched between two levels by controlling
the VID pin. When the VID pin is logic high, the internal NMOSFET turns on to set the output voltage to a lower
level. The output voltage can be calculated as below :
⎡ (R2//R3) ⎤
VOUT = 2V × ⎢
⎥
⎣ R1 + (R2//R3) ⎦
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RT8809
VREF
REF Generator
(2V)
TON
CCRCOT
On-Time
Computer
R1
VSET
R2
RTON
VIN
C1
RMPSET
R3
RRMP
RSET
GPIO
R1
On-Time
VID
Figure 2. On-Time Setting with RC Filter
Frequency vs. RTON
700
Figure 1. Output Voltage Setting with One Bit VID
Control
650
Switching Frequency Setting
Switching frequency is a trade-off between efficiency and
converter size. Higher operation frequency allows the use
of smaller components. This is common in ultra-portable
devices where the load currents are lower and the
controller is powered from a lower voltage supply. On the
other hand, lower frequency operation offers higher overall
efficiency at the expense of component size and board
space. Figure 2 shows the On-Time Setting Circuit.
Connect a resistor (RTON) from TON to VIN and a resistor
(R RMP) from RMPSET to GND to set the switching
frequency according to the formula below :
RTON
VIN − VSET
×
=
fS × C × VREF
VSET + IL × (RDS(ON)_L-MOS + RDC − RLL )
VIN + IL × (RDS(ON)_L-MOS − RDS(ON)_H-MOS )
where
fS : Switching frequency
RTON : TON setting resistor
C : Capacitance for on time compute
VREF : Reference voltage for on time compute
IL : Inductor current
RDS(ON)_L-MOS : RDS(ON) of Low-Side MOSFET
RDS(ON)_H-MOS : RDS(ON) of High-Side MOSFET
Frequency (kHz)1
600
550
500
450
400
350
300
250
200
150
0
50
100
150
200
250
300
RTON (k Ω )
Figure 3. Frequency vs. RTON
Current Sense Setting (with Temperature
Compensation)
The RT8809 uses continuous inductor current sensing to
make the controller less noise sensitive. Low offset
amplifiers are used for loop control and over current
detection. The CSP and CSN denote the positive and
negative input of the current sense amplifier of any phase.
Since the DCR of the inductor is temperature dependent,
it affects the down-phase threshold, OCP threshold and
output voltage accuracy, especially at heavy load.
Temperature compensation is recommended for the
lossless inductor DCR current-sense method. Figure 4
shows a simple but effective way to compensate the unwanted temperature variations of the inductor DCR by using
an NTC thermistor.
RDC : DCR of inductor
RLL : Load line resistance
The value of RTON can be selected using Figure 3 and the
value of RRMP must be set equal to RTON.
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RT8809
To calculate DCR value at different temperatures, can use
the equation below :
VOUT
L1
PHASE1
RS
L2
DCR
DCR
PHASE2
DCRT°C = DCR25°C x [1 + 0.00393 x( T-25)]
where the 0.00393 is the temperature coefficient of copper.
RNTC
RP
RS
CX can be obtained by below formula,
RX
CSP
CSN
⎛
⎞
RS
L ×⎜2 +
⎟
⎜
REQU_25°C ⎟⎠
⎝
CX =
RS × DCR25°C
CX
+
VX
-
(4)
COUT
(5)
Loop Control
LGATE1
CCRCOT
PWM
Driver
Logic
VIN
COUT
RX
UGATE2
PHASE2
L2
DCR
LGATE2
CMP
RX
VCS
+
GM
-
CSP
CX
CSN
C3
C2
C1
R2
R1
VSEN
(2)
1
α
−
REQU_TH REQU_TL
1
⎞ −⎛ 1 ⎞ ⎤ ⎫
⎟ ⎜
⎟
⎨ ⎢
⎥⎬
RNTC, T°C = R25°C × e⎩ ⎣⎝ T + 273 ⎠ ⎝ 278 ⎠ ⎦ ⎭
(3)
where R25°C is the thermistor's nominal resistance at room
temperature, β (beta) is the thermistor's material constant
in Kelvins, and T is the thermistor's actual temperature in
Celsius.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
FB
VRTN
VRTN
VREF
The standard formula for the resistance of the NTC
thermistor as a function of temperature is given by :
⎧ ⎡⎛
β ⎜
COMP
+
GM
-
where α is equal to DCRTH/DCRTL
DS8809-00 May 2013
L1 DCR
PHASE1
+
-
RS =
2(α -1)
VOUT
UGATE1
-
where R EQU_TH is equal to R P + R NTC // R X at high
temperature and REQU_TL is equal to RP + RNTC // RX at low
temperature. Usually, RX is set to equal RNTC (25°C). RP
and RX are selected to linearize the NTC's temperature
characteristic. For a given NTC and RP, the design is to
first obtain RS and then CX. Usually, set RX = RNTC. To
solve (1), RS must first be obtained as below :
VIN
+
The RT8809 observes the voltage VX, across the CSP and
CSN pins for inductor current information. To design VX
without regard to the temperature coefficient, refer to the
formula below :
RS
2+
R
DCRTH
EQU_TH
(1)
=
RS
DCRTL
2+
REQU_TL
The RT8809 adopts Richtek's proprietary G-NAVPTM
topology. G-NAVPTM is based on the finite-gain peak current
mode with CCRCOT (Constant Current Ripple Constant
On Time; CCRCOT) topology. The output voltage will
decrease with increasing output load current. The control
loop consists of PWM modulators with power stages,
current sense amplifiers and an error amplifier as shown
in Figure 5.
COMP2
Figure 4. Inductor DCR Sensing
Figure 5. Simplified Schematic for Droop and Remote
Sense in CCM
Similar to the peak current mode control with finite
compensator gain, the HS_FET on-time is determined by
the CCRCOT ON-Time generator. When the load current
increases, VCS increases, the steady state COMP voltage
also increases and VOUT decreases, achieving active
voltage positioning (AVP). RT8809 internally cancels the
inherent output offset of the finite gain peak current mode
controller.
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RT8809
Droop Setting
Due to the native droop characteristics, the active voltage
positioning (AVP) can be conveniently achieved by
properly setting the error amplifier gain. The target is to
have
VOUT = VREF − ILOAD x RLL
(6)
Then solving the switching condition VCOMP2 = VCS in
Figure 5 yields the desired error amplifier gain as
5 × DCR
R2
AV =
= 2
R1
RLL
(7)
where C is the capacitance of the output capacitor, and
RC is the ESR of output capacitor. C2 can be calculated
as follows :
C2 =
RC × C
R2
The zero of compensator has to be placed at half of the
switching frequency to filter the switching-related noise,
such that,
1
(10)
C1 =
R1× π × fS
Dynamic Phase Number Control
where RLL is the equivalent load line resistance as well as
the desired static output impedance. For a given R1, the
design is to get R2 according to (7).
VOUT
AV2 > AV1
The RT8809 controls the operation phase number according
to the total current. Figure 7 shows the dynamic phase
number control circuit. By connecting a resistor (RPS) from
the PS pin to GND, the phase transition threshold can be
set. The formula is :
RPS =
AV2
AV1
0
(9)
Load Current
Figure 6. Error Amplifier Gain (AV) Influence on VOUT
Accuracy
Loop Compensation
Optimized compensation of the RT8809 allows for best
possible load step response of the regulator's output. A
type-I compensator with a single pole and single zero is
adequate for a proper compensation. Figure 5 shows the
compensation circuit. Prior design procedure shows how
to determine the resistive feedback components of the
error amplifier gain, C1 and C2 must be calculated for the
compensation. The target is to achieve the constant
resistive output impedance over the widest possible
frequency range. The pole frequency, fP, of the compensator
must be set to compensate the output capacitor ESR
zero :
1
fP =
(8)
2π × RC × C
DCR × ISUM × 5
1μ
where ISUM is the sum of the inductor valley current. For
example, if DCR is 0.74mΩ, and the desired up-phase
threshold is 15A, the value of RPS will be
−3
RPS = 0.74 × 10 × 15 × 5 = 55.5kΩ
1× 10−6
Once the total inductor valley current is higher than the
threshold, the controller will transit to dual-phase operation.
when the total current becomes lower than the setting
threshold minus around 5A hysteresis, the active phase
number will return to single-phase. If the PS pin is set
floating, the controller will force to dual-phase operation.
PS
L1
L2
DCR
VPS
+
CMP
-
RPS
Active
Phase
Number
DCR
RX
RX
CX
COUT
CSN
CSP
gm
+
VCX
Figure 7. Dynamic Phase Number Control Circuit
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is a registered trademark of Richtek Technology Corporation.
DS8809-00 May 2013
RT8809
Current Balance
Under-Voltage Protection
The RT8809 implements internal current balance
mechanism in the current loop. The RT8809 senses perphase current signal 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.
The voltage on CSN pin is also monitored for under-voltage
protection. If the output voltage is lower than the UVP
threshold, UVP will be triggered. The RT8809 will then
turn off both high-side and low-side MOSFETs. When UVP
is triggered, the RT8809 will enter hiccup mode and
continuously try to restart until the UVP situation is
cleared.
Current Limit Setting
The RT8809 includes a built-in current limit protection
function. Figure 8 shows the protection circuit. The current
limit threshold is adjusted by an external resistor, ROC, at
the OCP pin. The value of ROC can be set according to
the following formula :
DCR × ISUM × 6
ROC =
8μ
where ISUM is the desired current limit threshold. Once
the sensed total current exceeds the current limit
threshold, the driver will be forced to turn off UGATE until
the OCP situation is removed.
Inductor Selection
The switching frequency and ripple current determine the
inductor value as follows :
V − VOUT
L(MIN) = IN
× TON
IRIPPLE(MAX)
where TON is the UGATE turn on period.
Higher inductance results in lower ripple current and higher
efficiency but brings a slower load transient response.
Thus, more output capacitors may be required. The lower
DC resistance can reduce power loss. The core must be
large enough and not to be saturated at the peak inductor
current.
Output Capacitor Selection
OCP
L1
L2
DCR
VOC
-
CMP
OCP
+
ROC
DCR
RX
RX
CX
COUT
CSN
CSP
gm
+
VCX
Figure 8. Over Current Protection Circuit
Over-Voltage Protection
The RT8809 monitors the output voltage via the CSN pin
for over-voltage protection (OVP). Once the output voltage
exceeds the OVP threshold, OVP is triggered. The RT8809
will turn on low-side MOSFETs and turn off high-side
MOSFETs to protect the load until the OVP situation is
removed. A 4μs delay is used in the OVP detection circuit
to prevent false trigger.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8809-00 May 2013
Output capacitors are used to maintain high performance
for the output beyond the bandwidth of the converter itself.
Two different kinds of output capacitors can be found, bulk
capacitors closely located to the inductors and ceramic
output capacitors close to the load. The latter ones are
for mid-frequency decoupling with especially small ESR
and ESL values while the bulk capacitors have to provide
enough stored energy to overcome the low-frequency
bandwidth gap between the regulator and the GPU.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
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RT8809
where TJ(MAX) is the maximum junction temperature, TA is
Layout Consideration
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Careful PC board layout is critical to achieving low
switching losses and clean, stable operation. The
switching power stage requires particular attention. If
possible, mount all of the power components on the top
side of the board with their ground terminals flushed
against one another. Follow these guidelines for optimum
PC board layout :
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WQFN-24L 4x4 package, the thermal resistance, θJA, is
35°C/W on a standard JEDEC 51-7 four-layer thermal test
board. The maximum power dissipation at TA = 25°C can
be calculated by the following formula :
P D(MAX) = (125°C − 25°C) / (28°C/W) = 3.57W for
WQFN-24L 4x4 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 8 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
`
Keep the high-current paths short, especially at the
ground terminals.
`
Keep the power traces and load connections short. This
is essential for high efficiency.
`
When trade-offs in trace lengths must be made, it’s
preferable to allow the inductor charging path to be made
longer than the discharging path.
`
Place the current sense components close to the
controller. CSP and CSN connections for current limit
and voltage positioning must be made using Kelvin sense
connections to guarantee the current sense accuracy.
The PCB trace from the sense nodes should be
paralleled back to the controller.
`
Route high-speed switching nodes away from sensitive
analog areas (COMP, FB, CSP, CSN, etc...)
Maximum Power Dissipation (W)1
4.0
Four-Layer PCB
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 8. Derating Curve of Maximum Power Dissipation
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is a registered trademark of Richtek Technology Corporation.
DS8809-00 May 2013
RT8809
Outline Dimension
D2
D
SEE DETAIL A
L
1
E
E2
e
b
A3
Symbol
D2
E2
1
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
A
A1
1
2
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.180
0.300
0.007
0.012
D
3.950
4.050
0.156
0.159
Option 1
2.400
2.500
0.094
0.098
Option 2
2.650
2.750
0.104
0.108
E
3.950
4.050
0.156
0.159
Option 1
2.400
2.500
0.094
0.098
Option 2
2.650
2.750
0.104
0.108
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 24L QFN 4x4 Package
Richtek Technology Corporation
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
DS8809-00 May 2013
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