RT8809A/B

RT8809A/B
Multi-Phase PWM Controller for GPU Core Power Supply
General Description
Features
The RT8809A/B 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
z
Dual-Phase PWM Controller
z
Two Embedded MOSFET Drivers and Embedded
Switching Boot Diode
Green-NAVP TM (Green Native Adaptive Voltage
Positioning) Topology
Dynamic Auto Phase Control with Programmable
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
Programmable OCP Threshold
Programmable 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
RT8809A/B 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 RT8809A/B also features a one-bit VID control
operation in which the feedback voltage is regulated and
tracks external input reference voltage. Other features
include, adjustable operating frequency, external
compensation, and enable/shutdown functions.
z
z
z
z
z
z
z
z
z
z
z
z
z
Ordering Information
z
RT8809A/B
Package Type
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
A : With Droop Function
B : Without Droop Function
Note :
z
Applications
z
z
z
z
Middle to High End GPU Core Power
High End Desktop PC Memory Core Power
Low Voltage, High Current DC/DC Converter
Voltage Regulator Modules
Pin Configurations
(TOP VIEW)
`
RSET
VID
BOOT2
UGATE2
PHASE2
LGATE2
Richtek products are :
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
24 23 22 21 20 19
VSET
VREF
EN/MSEL
RMPSET
COMP
FB
1
18
2
17
3
PGND
4
25
5
16
15
14
13
6
8
9 10 11 12
VRTN
TON
OCP
CSN
CSP
PS
7
VCC
VDD
LGATE1
PHASE1
UGATE1
BOOT1
WQFN-24L 4x4
DS8809A/B-02 July 2011
www.richtek.com
1
RT8809A/B
Marking Information
RT8809AGQW
RT8809BGQW
07= : Product Code
08= : Product Code
YMDNN : Date Code
07=YM
DNN
08=YM
DNN
RT8809AZQW
YMDNN : Date Code
RT8809BZQW
07 : Product Code
08 : Product Code
YMDNN : Date Code
07 YM
DNN
08 YM
DNN
YMDNN : Date Code
Typical Application Circuit
VIN
12V
RT8809A/B
17 VDD
C8
10µF
C4 Optional
C5
1.2nF
R18
11k
VRTN
R19
15k
EN/MODE
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
VCC 18
3 EN/MSEL
VID 23
BOOT2 22
UGATE2 21
PHASE2 20
PGND
FB
6
VRTN 7
www.richtek.com
2
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
C2
1.5nF
C1
2.2nF
R2
R1
3.9k
2k
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
R14
100
R15
100
VCC_SNS
VSS_SNS
DS8809A/B-02 July 2011
RT8809A/B
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VSET
Output Voltage Setting. Connect a voltage divider from VREF to VSET to set the
output voltage.
2
VREF
Reference Voltage Output (2V). RT8809A/B generates a 2V reference voltage from
VREF pin to VRTN.
Chip Enable and Mode Selection. This pin is a tri-state input. Pull up this pin to
exceed than 4.2V, 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.
Compensation Pin. This pin is the output node of the error amplifier.
3
EN/MSEL
4
RMPSET
5
COMP
6
FB
7
VRTN
8
TON
9
OCP
10
CSN
Feedback Pin. This pin is the negative input node of the error amplifier.
Remote Differential Feedback, Invert Input. This pin is the negative node of the
differential remote voltage sensing.
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
13
BOOT1
14
UGATE1
15
PHASE1
16
LGATE1
17
VDD
18
VCC
19
LGATE2
20
PHASE2
21
UGATE2
22
BOOT2
23
VID
24
RSET
25
PGND
(Exposed Pad)
DS8809A/B-02 July 2011
Dynamic Phase Control Input. Connect a resistor from PS to GND to set the auto
down phase threshold.
Bootstrap Power Pin of PHASE1. This pin powers the high side MOSFET driver.
Upper 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.
This pin is return node of the high side driver of PHASE1. Connect this pin to high
side MOSFET sources together with the low side MOSFET drain and the inductor.
Lower 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.
Internal Regulator Power. The regulated voltage provides power supply for all low
voltage circuits.
Chip/Driver Power Pin. Connect this pin to GND by a ceramic cap larger than 1μF.
Lower 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.
This pin is return node of the high side driver of PHASE2. Connect this pin to high
side MOSFET sources together with the low side MOSFET drain and the inductor.
Upper 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.
Bootstrap Power Pin of PHASE2. This pin powers the high side MOSFET driver.
Programming Output Voltage Control. When VID pin is logic high, internal
N-MOSFET that connected to RSET pin is turn on.
Output Voltage Setting. Connect a resistor from RSET pin to VSET pin, the output
voltage can be switched two level by driving VID pin.
The exposed pad must be soldered to a large PCB and connected to GND for
maximum power dissipation.
www.richtek.com
3
RT8809A/B
Function Block Diagram
RT8809A (With Droop Function)
VID
VREF
RSET
VCC
Reference
Output Gen.
Internal
Regulator&BG
VDD
Power On Reset
& Central Logic
UV Trip Point
VSET
+
-
OV Trip Point
Control & Protection Logic
+
-
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
+
+
+
PWM1
+
+
To Power
on Reset
To driver Logic
ZCD
To Power on
Reset
PHASE1 To driver Logic
5
APS
www.richtek.com
4
-
TON
Gen 2
BOOT2
UGATE2
PHASE2
PWM2
LGATE2
PGND
S/H
GM
+
S/H
GM
+
Current
Balance
PS
+
LGATE1
Driver
Logic
VIN
Detection
TON
CSP
CSN
OCP
BOOT1
UGATE1
PHASE1
TON
Gen 1
PWM
CMP
AOC
Isum
Phase
shedding
OCP
+
1/2
VB
++
To Protection Logic
DS8809A/B-02 July 2011
RT8809A/B
RT8809B (Without Droop Function)
VID
VREF
RSET
VCC
Reference
Output Gen.
Internal
Regulator&BG
VDD
Power On Reset
& Central Logic
VSET
UV Trip Point
+
-
OV Trip Point
Control & Protection Logic
+
-
Boot-Phase
Detection 1
Ramp
Gen
RMPSET
Boot-Phase
Detection 2
VSETA
VRTN
Soft-Start
+
FB
ERROR
AMP
COMP
EN/MSEL
EN/Mode
Select
+
+
+
+
+
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
APS
CSP
CSN
OCP
DS8809A/B-02 July 2011
+
-
BOOT2
UGATE2
PHASE2
AOC
Isum
Phase
shedding
OCP
+
1/2
++
To Protection Logic
www.richtek.com
5
RT8809A/B
Absolute Maximum Ratings
z
z
z
z
z
z
z
z
z
z
z
z
z
(Note 1)
VDD, VSEN, COMP, VSET, VREF, EN/MSEL, PS, OCP, CSN,
CSP, RSET, VID, RMPSET to PGND ------------------------------------------------------------ −0.3V to 6V
VCC, TON to PGND --------------------------------------------------------------------------------- −0.3V to 15V
VRTN to PGND ---------------------------------------------------------------------------------------- −0.3V to 0.3V
BOOTx to PHASEx ---------------------------------------------------------------------------------- −0.3V to 15V
PHASEx to PGND
DC -------------------------------------------------------------------------------------------------------- −3V to 15V
<20ns --------------------------------------------------------------------------------------------------- −5V to 30V
UGATEx to PHASEx
DC -------------------------------------------------------------------------------------------------------- −0.3V to BOOTx − PHASEx
<20ns --------------------------------------------------------------------------------------------------- −5V to (BOOTx − PHASEx + 5V)
LGATEx to PGND
DC -------------------------------------------------------------------------------------------------------- −0.3V to PVCC+ 0.3V
<20ns --------------------------------------------------------------------------------------------------- −5V to (VCC + 5V)
Power Dissipation, PD @ TA = 25°C
WQFN-24L 4x4 --------------------------------------------------------------------------------------- 1.923W
Package Thermal Resistance (Note 2)
WQFN-24L 4x4, θJA ---------------------------------------------------------------------------------- 52°C/W
WQFN-24L 4x4, θJC --------------------------------------------------------------------------------- 7°C/W
Junction Temperature -------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------- 260°C
Storage Temperature Range ----------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) ------------------------------------------------------------------------- 2kV
MM (Machine Mode) --------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
z
z
z
(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
www.richtek.com
6
DS8809A/B-02 July 2011
RT8809A/B
Electrical Characteristics
(VCC = 12V, No Load, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Supply Input
Supply Current
IVCC + IPVCC EN = 3.3V, Not Switching
--
4
--
mA
Shutdown Current
ICC + IPVCC
EN = 0V
--
--
500
μA
VVCC_th
VCC Rising
--
4.2
--
V
--
0.4
--
V
--
2
--
−1%
--
1%
0.5
--
2
V
--
1.5
--
ms
--
300
--
μs
--
10
--
mV/μs
−8
--
8
mV
RL = 47kΩ
--
80
--
dB
CLOAD = 5pF
CLOAD = 10pF (Gain = −4,
Rf = 47k, VOUT = 0.5V to 3V)
--
10
--
MHz
--
5
--
V/μs
0.5
--
2
V
--
250
--
μA
Power On Reset
VCC POR Threshold
Power On Reset Hysteresis VVCC_hys
Reference
Reference Output
VREF
Reference Input Range
VSET
(No Load, Active Mode )
Accuracy
VSET pin (this max. voltage will affect
VCOMP max.)
V
Start Up Delay
Initial Soft-Start time
Reference Change Delay
Time
Internal VID Change Slew
Rate (RT8809A Only)
Error Amplifier
tb
Input Offset Voltage
VOSEA
Initially, VOUT = 0.1V to 1.2V
tc
td
DC Gain
VOUT = 1.2V to Set Voltage
Gain Bandwidth Product
GBW
Slew Rate
SR
Output Voltage Range
VCOMP
RL = 47kΩ (max. depend on VSET max.)
MAX Source Current
IOUTEA
VCOMP = 2V
Current Sense Amplifier (for Droop and OCP and Phase Shedding)
Input Offset Voltage
VOSCS
−1
--
1
mV
Impedance at Neg. Input
RCSN
1
--
--
MΩ
Impedance at Pos Input
RCSP
1
--
--
MΩ
---
5
0
---
V/V
−50
--
100
mV
DC Gain
RT8809A
RT8809B
Input range
VCSP − VCSN
TON Setting
TON Pin Output Voltage
VTON
IRTON = 62μA
--
VSET
--
V
ON-Time Setting
TON
IRTON = 62μA
--
350
--
ns
TON Input Current Range
I RTON
25
--
280
μA
Protection
Under Voltage Lockout
Threshold
VUVLO
--
3.8
--
V
Falling edge
To be continued
DS8809A/B-02 July 2011
www.richtek.com
7
RT8809A/B
Parameter
Symbol
Test Conditions
Absolute Over
RT8809A/BGQW
VOVABS With Respect to VOUT(MAX)
Voltage Protection
RT8809A/BZQW
Threshold
Min
Typ
Max
2.1
2.2
--
2.6
2.9
--
--
138
--
%
--
50%
--
%
VNV
−50
--
--
mV
IOCP
7.2
8
8.8
μA
--
--
0.5
V
ASM Mode
1.2
--
3
DEM Mode
4.2
--
--
−1
--
5
μA
--
8
--
μA
--
500
--
ns
VBOOTx − VPHASEx = 6V
V
− VPHASEx = 0.1V,
R UGATEsk UGATEx
IUGATEx = 50Ma
--
1.2
--
A
--
2
--
Ω
Lower Driver Source
Lower Driver Sink
ILGATEsr VCC − VLGATEx = 6V
R LGATEsk VLGATEx = 0.1V, ILGATEx = 50mA
---
1.2
1.4
---
A
Ω
Internal Boost Charging Switch
On-Resistance
R BOOT
--
20
--
Ω
Relative Over Voltage Protection
Threshold
VREL_OV With Respect to VOUT
Under Voltage Protection Threshold
VUV
Negative Voltage Protection
Threshold
Current Source by OCP Pin
Measured at VSENS with Respect
to Unloaded Output Voltage (UOV)
Unit
V
Logic Inputs
EN Threshold Voltage
VIL
EN Pin Mode Select Voltage
Low Level (SD) (Hysteresis)
Leakage Current of EN
V
Auto Phase Control
Current Source by PSI Pin
IPS
Maximum Duty Cycle
UGATE Min. Off Time
Gate Driver
Upper Driver Source
Upper Driver Sink
IUGATEsr
PVCC to BOOTx
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in natural convection at TA = 25°C on a high effective four-layers thermal conductivity test board of
JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on 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.
www.richtek.com
8
DS8809A/B-02 July 2011
RT8809A/B
Typical Operating Characteristics
Efficiency vs. Load Current
Efficiency vs. Load Current
100
100
90
90
80
Phase 2 Active
70
Efficiency (%)
Efficiency (%)
80
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)
1
10
Load Current (A)
TON vs. Temperature
VREF vs. Temperature
360
2.04
355
2.03
350
2.02
VREF (V)
TON (ns)
345
340
335
330
2.01
2.00
1.99
1.98
325
320
VIN = VCC = 12V, No Load
315
-50
-25
0
25
50
75
100
125
1.97
-50
-25
0
25
50
75
Temperature (°C)
Temperature (°C)
Inductor Current vs. Output Current
Power On from EN
35
100
125
RT8809A, VIN = VCC = 12V, IOUT = 50A
30
Inductor Current (A)
VIN = VCC = 12V, No Load
1.96
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)
DS8809A/B-02 July 2011
www.richtek.com
9
RT8809A/B
Power On from EN
Power Off from EN
RT8809B, VIN = VCC = 12V, IOUT = 50A
VIN = VCC = 12V, IOUT = 50A
VEN
(10V/Div)
VEN
(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 On from VCC
Power On from VCC
RT8809A, VIN = VCC = 12V, IOUT = 50A
RT8809B, VIN = VCC = 12V, IOUT = 50A
V CC
(10V/Div)
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
RT8809A, VSET = 0.78V to 1.15V, IOUT = 40A
VIN = VCC = 12V, IOUT = 50A
V CC
(10V/Div)
VSET
(1V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
Time (1ms/Div)
www.richtek.com
10
Time (40μs/Div)
DS8809A/B-02 July 2011
RT8809A/B
Dynamic Output Voltage Control
Dynamic Output Voltage Control
RT8809B, VSET = 0.78V to 1.15V, IOUT = 40A
RT8809A, VSET = 1.15V to 0.78V, IOUT = 40A
VSET
(1V/Div)
VSET
(1V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
Time (200μs/Div)
Time (40μs/Div)
Dynamic Output Voltage Control
Load Transient Response
RT8809A, VIN = VCC = 12V, RLL = 1.5mΩ
RT8809B, VSET = 1.15V to 0.78V, IOUT = 40A
VSET
(1V/Div)
VOUT
(500mV/Div)
VOUT
(1V/Div)
IOUT
(50A/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
Time (200μs/Div)
Time (10μs/Div)
Load Transient Response
Load Transient Response
RT8809B, VIN = VCC = 12V
RT8809A, VIN = VCC = 12V, RLL = 1.5mΩ
VOUT
(500mV/Div)
VOUT
(500mV/Div)
IOUT
(50A/Div)
IOUT
(50A/Div)
UGATE1
(50V/Div)
UGATE1
(50V/Div)
UGATE2
(50V/Div)
UGATE2
(50V/Div)
Time (10μs/Div)
DS8809A/B-02 July 2011
Time (10μs/Div)
www.richtek.com
11
RT8809A/B
OVP
Load Transient Response
VIN = VCC = 12V, IOUT = 25A
RT8809B, VIN = VCC = 12V
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)
www.richtek.com
12
Time (10ms/Div)
DS8809A/B-02 July 2011
RT8809A/B
Application Information
RT8809A/B is a dual-phase synchronous buck PWM
controller with integrated drivers which is optimized for highperformance 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 is easily designed
and the component count is reduced.
RT8809A/B adopts G-NAVPTM (Green-Native Adaptive
Voltage Positioning), which is Richtek's proprietary
topology derived from finite DC gain compensator with
current mode control for RT8809A, the load line can be
easily programmed by setting the DC gain of the error
amplifier for RT8809B, the load line is fixed to zero.
RT8809A/B also adopts lossless DCR and RDS(ON) current
sensing. Voltage positioning (only for RT8809A), 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.
RT8809A/B supports dynamic mode transition function with
various operating states, which include dual-phase, single
phase, diode emulation and audio skipping modes. These
different operating states make the system efficiency as
high as possible.
RT8809A/B provides a one-bit VID control operation in which
the feedback voltage is regulated and tracks external input
reference voltage. It also features complete fault protection
functions including over voltage, under voltage 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 RT8809A/B can
switch operation into DEM when EN/MSEL pin is pulled
up to above 4.2V. In DEM operation, RT8809A/B
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 30 kHz to avoid the acoustic noise.
Finally, if the pin is pulled to GND the RT8809A/B will
shutdown.
DS8809A/B-02 July 2011
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 enable. During
soft-star period, the output voltage will first boot to around
1V, and then change to the set level when using RT8809A.
For RT8809B, output voltage will directly ramp 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
RT8809A/B 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 internal soft-start capacitor such that the
internal soft-start voltage ramps up in a monotone to a
VBOOT voltage RT8809A or the set level (RT8809B). 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 dualphase 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. RT8809A/B 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 below calculation :
VOUT = 2V × ⎛⎜ R2 ⎞⎟
⎝ R1 + R2 ⎠
RT8809A/B 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 N-MOSFET
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) ⎦
www.richtek.com
13
RT8809A/B
One-Bit VID and Dynamic Output Voltage Control
C : Capacitance for on time compute (13.7pF)
In RT8809A, the dynamic VID slew rate is fixed to 10mV/
μs. For RT8809B, it can be set lower than 10mV/μs by
CVSET as shown in Figure 1. That is, assume the ΔVOUT =
300mV, R1=11kΩ, R2 = R3 = 27kΩ, the desired slew
rate at falling is SRF = 10mV/μs, and the CVSET can be
calculated by below formula.
ΔVOUT
C VSET =
= 1nF
5 × (R1 // R2 // R3 ) × SRF
VREF : Reference voltage for on time compute
And then, the rising slew rate SRR will be
SRR =
ΔVOUT
= 7.67mV/μS
5 × (R1 // R2 ) × C VSET
IL : Inductor current
RDS(ON)_L-MOS : RDS(ON) of Low Side MOSFET
RDS(ON)_H-MOS : RDS(ON) of High Side MOSFET
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.
TON
VREF
CCRCOT
On-Time
Computer
REF Generator
(2V)
R1
RTON
CVSET
R3
GPIO
VIN
C1
RMPSET
VSET
R2
R1
RRMP
On-Time
RSET
Figure 2. On-Time Setting with RC Filter
VID
Frequency vs. RTON
700
Figure 1. Output Voltage Setting with One Bit VID
Control
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, 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 (RRMP) from RMPSET
to GND to set the switching frequency according to below
formula :
VIN − VSET
×
RTON =
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
www.richtek.com
14
600
Frequency (kHz)1
Adjustable Switching Frequency
650
550
500
450
400
350
300
250
200
150
0
50
100
150
200
250
300
RTON (Ω)
Ω
Figure 3. Frequency vs. RTON
Current Sense Setting (with Temperature
Compensation)
The RT8809A/B 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
DS8809A/B-02 July 2011
RT8809A/B
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.
VOUT
L2
PHASE2
RP
RS
CSP
CX can be obtained by below formula,
COUT
RNTC
⎛
RS
L× ⎜ 2 +
⎜
REQU_25°C
⎝
CX =
RS × DCR25°C
RX
+
VX
-
CSN
DCR
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 :
REQU_TH
−
The RT8809A/B 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. For RT8809A, the output
voltage will decrease with increasing output load current.
For RT8809B, the output voltage is independent with 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.
VIN
VOUT
UGATE1
CCRCOT
PWM
Driver
Logic
LGATE1
VIN
UGATE2
PHASE2
CMP
RT8809A
+
GM
-
RNTC, T°C = R25°C
DS8809A/B-02 July 2011
CX
CSN
+
GM
-
(3)
C3
C2
C1
R2
R1
VSEN
REQU_TL
⎧ ⎡⎛ 1 ⎞ ⎛ 1 ⎞ ⎤ ⎫
⎟ −⎜
⎟⎥ ⎬
⎨ β ⎢⎜
× e⎩ ⎣⎝ T + 273 ⎠ ⎝ 278 ⎠ ⎦ ⎭
DCR
CSP
COMP
The standard formula for the resistance of the NTC
thermistor as a function of temperature is given by :
L2
RX
VCS
(2)
Where α is equal to DCRTH/DCRTL
COUT
RX
LGATE2
RT8809B
α
L1 DCR
PHASE1
FB
+
-
1
(5)
Loop Control
The RT8809A/B 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
below formula :
RS
2+
REQU_TH
DCRTH
(1)
=
RS
DCRTL
2+
REQU_TL
2(α -1)
⎞
⎟⎟
⎠
CX
Figure 4. Inductor DCR Sensing
RS =
(4)
where the 0.00393 is the temperature coefficient of copper.
-
RS
DCRT°C = DCR25°C x [1 + 0.00393 x ( T − 25) ]
DCR
+
PHASE1
To calculate DCR value at different temperatures, can use
the equation below :
COMP2
L1
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.
VREF
VRTN
VRTN
Figure 5. Simplified Schematic for Droop and Remote
Sense in CCM
www.richtek.com
15
RT8809A/B
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). RT8809A/B internally cancels
the inherent output offset of the finite gain peak current
mode controller.
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
Droop Setting
where C is the capacitance of the output capacitor, and
RC is the ESR of output capacitor. C2 can be calculated
as follows :
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 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). And the R2 should
be greater than 1.4kΩ.
VOUT
AV2 > AV1
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
The RT8809A/B 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
Load Current
Figure 6. Error Amplifier Gain (AV) Influence on VOUT
Accuracy
Note that the droop function is not available for the
RT8809B
Loop Compensation
Optimized compensation of the RT8809A/B 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
www.richtek.com
16
(9)
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.
DS8809A/B-02 July 2011
RT8809A/B
Over Voltage Protection
PS
L1
L2
+
CMP
-
RPS
DCR
Active
Phase
Number
DCR
RX
RX
VPS
CX
COUT
CSN
CSP
VCX
gm
+
The RT8809A/B 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 RT8809A/B will try to 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.
Under Voltage Protection
Figure 7. Dynamic Phase Number Control Circuit
Current Balance
The RT8809A/B implements internal current balance
mechanism in the current loop. The RT8809A/B senses
per 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.
Current Limit Setting
The RT8809A/B includes a built-in builds-in current limit
protection function. Figure 8 shows the protection circuit.
The current limit threshold is programmable 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.
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 RT8809A/B will then
turn off both high side and low side MOSFETs. When
UVP is triggered, The RT8809A/B will enter hiccup mode
and continuously try to restart until the UVP situation is
cleared.
Inductor Selection
The switching frequency and ripple current determine the
inductor value as follows :
L(MIN) =
VIN − VOUT
× TON
IRIPPLE(MAX)
where TON is the UGATE turn on period.
Higher inductance results in achieves lower ripple current
and hence in higher efficiency but with a slower load
transient response as a, trade off. Thus, a need for more
output capacitors may be required, driving the cost up.
Find a low loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. The core
must be large enough not to be saturated at the peak
inductor current.
Output Capacitor Selection
OCP
L1
L2
DCR
-
CMP
OCP
+
ROC
DCR
RX
RX
VOC
CX
COUT
CSN
CSP
gm
+
VCX
Figure 8. Over Current Protection Circuit
DS8809A/B-02 July 2011
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 in close proximity to the load. 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 lowfrequency bandwidth gap between the regulator and the
GPU.
www.richtek.com
17
RT8809A/B
Thermal Considerations
Layout 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 :
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 :
PD(MAX) = (TJ(MAX) − TA) / θJA
`
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
`
For recommended operating condition specifications of the
RT8809A/B, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θJA, is layout dependent. For WQFN24L 4x4 package, the thermal resistance, θJA, is 52°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 :
`
`
PD(MAX) = (125°C − 25°C) / (52°C/W) = 1.923W for
WQFN-24L 4x4 package
`
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. For the RT8809A/B package, the derating
curve in Figure 9 allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
Maximum Power Dissipation (W)1
2.0
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...)
Four-Layer PCB
1.6
1.2
0.8
0.4
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 9. Derating Curves for the RT8809A/B Package
www.richtek.com
18
DS8809A/B-02 July 2011
RT8809A/B
Outline Dimension
D2
D
SEE DETAIL A
L
1
E
E2
e
b
1
1
2
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
A
A3
A1
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
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
D2
2.300
2.750
0.091
0.108
E
3.950
4.050
0.156
0.159
E2
2.300
2.750
0.091
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
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: [email protected]
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design,
specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed
by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
DS8809A/B-02 July 2011
www.richtek.com
19