RT8800A
General Purpose 3-Phase PWM Controller for High-Density
Power Supply
General Description
The RT8800A is a general-purposed multi-phase
synchronous buck controller dedicating for high power
density applications. The RT8800A operates with 2 or 3
synchronous buck switching stages in interleaved phase
set automatically. The multiphase architecture provides
high output current while maintaining low power dissipation
on power devices and low stress on input and output
capacitors.
The output voltage is precisely regulated to the external
reference voltage at PI pin. The RT8800A can provide Intel
®
VRD10.x or AMD
®
K8 compliant output voltage when
companioned with DAC generator RT9401A/B.
The RT8800A adopts innovative time-sharing DCR current
sensing technique for channel current balance, droop
tuning, and over current protection. Using one common
GM amplifier for current sensing eliminates offset errors
and linearity variation between GMs. As sub-milli-ohm-
grade inductors are widely used in modern mother boards,
slight mismatch of GM amplifiers offset and linearity results
in considerable current shift between phases. The time-
sharing DCR current sensing technique is extremely
important to guarantee phase current balance at mass
production.
Other features include overvoltage protection, undervoltage
protection and internal softstart. The RT8800A comes to
a VQFN-16L 3x3 package.
Features
5V Power Supply Voltage
2/3-Phase Power Conversion with Automatic Phase
Selection
Output Voltage Controlled by External Reference
Voltage
Precise Core Voltage Regulation
Power Stage Thermal Balance by DCR Current
Sensing
Extreme Low-Cost, Lossless Time Sharing Current
Sensing
Internal Soft-Start
Hiccup Mode Over-Current Protection
Over-Voltage Protection
Adjustable Operating Frequency and Typical at
300kHz Per Phase
Power Good Indication
Small 16-Lead VQFN Package
RoHS Compliant and 100% Lead (Pb)-Free
Applications
Desktop CPU Core Power
Low Output Voltage, High Power Density DC-DC
Converters
Voltage Regulator Modules
Marking Information
Ordering Information
RT8800A
Package Type
QV : VQFN-16L 3x3 (V-Type)
Operating Temperature Range
P : Pb Free with Commercial Standard
G : Green (Halogen Free with Commer-
cial Standard)
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
Note :
Richtek Pb-free and Green 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.
100% matte tin (Sn) plating.
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DS8800A-04 August 2007
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1
RT8800A
Pin Configurations
(TOP VIEW)
PWM3
PWM2
PWM1
12
ISP1
11
ISP2
10
ISP3
9
8
IMAX
VID125
FB
DVD
1
2
3
4
5
6
7
VDD
16 15 14 13
GND
17
PGOOD
PI
RT
VQFN-16L 3x3
Functional Pin Description
IMAX (Pin 1)
Over current protection setting.
VID125 (Pin 2)
Connect a resistor from this pin to GND can raise V
OUT
.
FB (Pin 3)
The pin is defined as the inverting input of internal error
amplifier.
DVD (Pin 4)
The pin is defined as a programmable power UVLO
detection input. Trip threshold = 0.8V at V
DVD
rising.
COMP (Pin 5)
The pin is defined as the output of the error amplifier and
the input of all PWM comparators.
PI (Pin 6)
The pin is defined as the positive input of the error amplifier.
RT (Pin 7)
Switching frequency setting. Connect this pin to GND with
a resistor to set the frequency.
VDD (Pin 16)
Chip power supply. Connect this pin to a 5V supply.
GND [Exposed Pad (17)]
The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
PGOOD (Pin 9)
Output power-good indication. The signal is implemented
as an output signal with open-drain type.
ISP1 , ISP2 , ISP3 (Pin 12, Pin 11, Pin 10)
Current sense positive inputs for individual converter
channel current sense.
PWM1 , PWM2 , PWM3 (Pin 13, Pin 14, Pin 15)
PWM outputs for each phase switching drive.
ICOMMON (Pin 8)
Common negative input of current sense amplifiers for all
three channels.
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2
DS8800A-04 August 2007
ICOMMON
COMP
PHASE2
L1
0.5uH
12V
V
IN
Q3
Q1
Q2
C17
R13
0
12V
1uF
R15
0
C25 to C36
1000uF x 12
D1
C11 to C14
1500uF x 4
C15
1uF
1uH
C9
1000uF
C10
1uF
5V
C5
4.7uF
R14 2.2
C16
3.3uF
Typical Application Circuit
PVCC2
UGATE2
PHASE2
LGATE2
R1
15k
C2
10nF
R3 3k
TS
PHASE1
PVCC1
LGATE1
ICOMMON
3.3V
DVD 4
RT 7
12V
R8
3k
R12
PHASE1
D2
Q4
12V V
IN
R
C8
1uF
Optional
R
COMM
430
Optional
R
CSN
D
SKY
R9
16k
C7
1uF
R
C18
1uF
R16
0
R7
27k
12V
Optional
R11
PHASE2
1
UGATE1
24
22
23
C19
1uF
8
R19 10
R18
0
C20 1uF
VDD
DS8800A-04 August 2007
3-phase with RT9401A/B DAC generator
C1
33pF
Optional
C3
R2
17
19
20
3
21
Q7
PHASE3
C24
3.3nF
Q8
R22
2.2
R21
0
L2
0.5uH
16
5
16
BOOT2
RT9605
PVCC3
GND
PHASE3
UGATE3 10
BOOT3
9
C23
1uF
12V
3
LGATE3
15
11
12V
FB
7
15
5
PWM2
PWM1
BOOT1
4
R10
Optional
PHASE3
R
C6 1uF
R20
14
0
C22
1uF
C37 to C40
10uF x 4
VDD
13 PWM1
COMP
R
ADJ
6
RT8800A
GND
ISP3
2
ISP2
ISP1
11
10
PWM2
14
PWM3
PI
PWM3
C4
10nF
R4 10k
1 IMAX
V
CORE
Q9
R5 16k
2
VID125
R6 10k
9
PGOOD
V
IN
12
8
5V
SB
PHASE1
L3
0.5uH
Q5
R17 2.2
C21
3.3nF
Q6
1
RT9401A/B
VID2
VID3
8
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R
CS
V
CORE
2
VID1
VID4
7
3
VDA
GND
6
5V
4
VDD
VID0
5
RT8800A
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3
Function Block Diagram
Oscillator
&
Ramp Generator
PWM Logic
& Driver
+
+
PWMCP
INH
PWM Logic
& Driver
-
+
+
-
+
+
+
+
EA
+
-
FB
PI
500mV
OVP
0.8V
V
REF
+
Mux
OCP
Sample
& Hold
Sample
& Hold
Mux
Sample
& Hold
MAJ
SUM/N
& OCP
Detection
-
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INH
Power On
Reset
Soft Start
+
+
PWMCP
INH
PWM Logic
& Driver
-
+
+
VID125
DS8800A-04 August 2007
IMAX
GND
+
GM
-
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PGOOD VDD DVD
RT
PWM1
PWM2
PWM3
PWMCP
ICOMMON
ISP1
ISP2
ISP3
RT8800A
COMP
RT8800A
Absolute Maximum Ratings
(Note 1)
Supply Voltage, V
DD
------------------------------------------------------------------------------------------- 7V
Input, Output or I/O Voltage ---------------------------------------------------------------------------------- GND
−
0.3V to V
DD
+ 0.3V
Power Dissipation, P
D
@ T
A
= 25°C
VQFN-16L 3x3 -------------------------------------------------------------------------------------------------- 1.47W
Package Thermal Resistance (Note 4)
VQFN-16L 3x3,
θ
JA
--------------------------------------------------------------------------------------------- 68°C/W
Junction Temperature ------------------------------------------------------------------------------------------ 150°C
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 2)
HBM (Human Body Mode) ----------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 3)
Supply Voltage, V
DD
------------------------------------------------------------------------------------------- 5V
±
10%
Ambient Temperature Range --------------------------------------------------------------------------------- 0°C to 70°C
Junction Temperature Range --------------------------------------------------------------------------------- 0°C to 125°C
Electrical Characteristics
(V
DD
= 5V, T
A
= 25°C, unless otherwise specified)
Parameter
V
DD
Supply Current
Nominal Supply Current
Power-On Reset
V
DD
Threshold
Rising
Hysteresis
Symbol
Test Conditions
Min
Typ
Max
Units
I
DD
PWM 1,2,3 Open
--
5
4.2
0.5
0.8
65
--
4.5
--
0.85
--
mA
V
V
V
mV
4.0
0.2
0.75
--
DVD Rising Threshold
DVD Hysteresis
Oscillator
Free Running Frequency
Frequency Adjustable Range
Ramp Amplitude
Ramp Valley
Maximum On-Time of Each Channel
RT Pin Voltage
Reference Voltage
IMAX Reference Voltage
VID125 Reference Voltage
V
IMAX
V
VID125
R
IMAX
= 16kΩ
R
VID125
= 16kΩ
V
RT
R
RT
= 16kΩ
f
OSC
f
OSC_ADJ
ΔV
OSC
V
RV
R
RT
= 16kΩ
R
RT
= 16kΩ
170
50
--
--
62
0.77
200
--
1.7
1.0
66
0.82
230
400
--
--
75
0.87
kHz
kHz
V
V
%
V
0.75
0.75
0.8
0.8
0.85
0.85
V
V
To be continued
All brand name or trademark belong to their owner respectively
DS8800A-04 August 2007
www.richtek.com
5