RT8228B
Single Synchronous Buck PWM Controller
General Description
The RT8228B PWM controller provides high efficiency,
excellent transient response, and high DC output accuracy
needed for stepping down high voltage batteries to
generate low voltage CPU core, I/O, and chipset RAM
supplies in notebook computers.
The constant on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on”
response to load transients while maintaining
a relatively constant switching frequency.
The RT8228B achieves high efficiency at a reduced cost
by eliminating the current sense resistor found in
traditional current mode PWMs. Efficiency is further
enhanced by its ability to drive very large synchronous
rectifier MOSFETs and enter diode emulation mode at
light load condition. The buck conversion allows this device
to directly step down high voltage batteries at the highest
possible efficiency. The RT8228B is intended for CPU core,
chipset, DRAM, or other low voltage supplies as low as
0.5V. The RT8228B is available in a WQFN-12L 2x2
package.
Features
Built in 1% 0.5V Reference Voltage
Adjustable 0.5V to 3.3V Output Range
Support Pure MLCC Output Capacitor
Quick Load Step Response within 100ns
4700ppm/°C Programmable Current Limit by Low
°
Side R
DS(ON)
Sensing
4.5V to 26V Battery Input Range
Resistor Programmable Frequency
Internal Ramp Current Limit Soft-Start Control
Drives Large Synchronous Rectifier FETs
Integrated Boost Switch
Over/Under Voltage Protection
Thermal Shutdown
Power Good Indicator
RoHS Compliant and Halogen Free
Applications
Notebook Computers
CPU Core Supply
Chipset/RAM Supply as Low as 0.5V
Generic DC/DC Power Regulator
Ordering Information
RT8228B
Package Type
QW : WQFN-12L 2x2 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
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.
Pin Configurations
(TOP VIEW)
GND
12
TON
11
LGATE
PHASE
UGATE
CS
10
9
1
2
3
4
5
PGOOD
EN
MODE
GND
13
6
8
7
BOOT
WQFN-12L 2x2
RT8228B-05 October 2011
VCC
FB
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1
RT8228B
Marking Information
RT8228BGQW
44 : Product Code
RT8228BZQW
44 : Product Code
W : Date Code
44W
44W
W : Date Code
Typical Application Circuit
R
TON
360k
R4
0
R5
0
C3
0.1µF
V
IN
4.5V to 26V
C4
10µF
11
RT8228B
BOOT 4
TON
VCC
UGATE 3
PHASE 2
1
LGATE
VDDP
R2
100k
5
C2
4.7µF
Q1
L1
1µH
R7*
C7*
R8
10k
V
OUT
1V
* : Optional
C5* C6*
Q2
C1
22µF
C8
22µF
C9
22µF
C10
22µF
PGOOD
R6
9
PGOOD
10 CS
FB 6
7
MODE
To 5V : DEM
To GND : FCCM
R9
10k
Chip Enable
8
EN
GND
12, 13 (Exposed Pad)
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RT8228B-05 October 2011
RT8228B
Functional Pin Description
Pin No.
1
2
3
4
5
6
7
8
9
10
11
Pin Name
LGATE
PHASE
UGATE
BOOT
VCC
FB
MODE
EN
PGOOD
CS
TON
Pin Function
Gate Drive Output for Low Side External MOSFET.
External Inductor Connection Pin for PWM Converter. It behaves as the current
sense comparator input for Low Side MOSFET R
DS(ON)
sensing and reference
voltage for on time generation.
Gate Drive Output for High Side External MOSFET.
Supply Input for High Side Driver. Connect through a capacitor to the floating
node (PHASE) pin.
Control Voltage Input. Provides the power for the buck controller, the low side
driver and the bootstrap circuit for high side driver. Bypass to GND with a 4.7μF
ceramic capacitor.
V
OUT
Feedback Input. Connect FB to a resistive voltage divider from V
OUT
to
GND to adjust the output from 0.5V to 3.3V
Pull Down to GND for Forced CCM Mode.
Pull Up to 5V for Diode Emulation Mode (DEM).
PWM Chip Enable. Pull low to GND to disable the PWM.
Open Drain Power Good Indicator. High impedance indicates power is good.
Current Limit Threshold Setting Input. Connect a setting resistor to GND and the
current limit threshold is equal to 1/10 of the voltage at this pin.
On-time Setting. Connect a resistor between this pin and V
IN
.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
12,
GND
13 (Exposed Pad)
Function Block Diagram
TRIG
On-time
Compute
1-SHOT
PSR
-
COMP
+
TON
PHASE
BOOT
R
S
Q
PWM
DRV
UGATE
PHASE
VCC
DRV
LGATE
GND
DEM/FCCM
MODE
PGOOD
0.5V V
REF
+
-
-
OV
125% V
REF
FB
70% V
REF
Latch
S1
Q
Latch
S1
Q
Min. T
OFF
Q
TRIG
1-SHOT
UV
+
125% V
REF
SS
Timer
-
+
-
VCC
EN
POR
90% V
REF
+
+
-
10µA
CS
Thermal
Shutdown
X(-1/10)
RT8228B-05 October 2011
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3
RT8228B
Absolute Maximum Ratings
(Note 1)
VCC to GND --------------------------------------------------------------------------------------------------------
–0.3V
to 6V
FB, PGOOD, EN, CS, MODE to GND -----------------------------------------------------------------------
–0.3V
to (VCC + 0.3V)
TON to GND --------------------------------------------------------------------------------------------------------
–0.3V
to 32V
BOOT to PHASE -------------------------------------------------------------------------------------------------
–0.3V
to 6.5V
PHASE to GND
DC --------------------------------------------------------------------------------------------------------------------
−0.3V
to 32V
< 20ns ---------------------------------------------------------------------------------------------------------------
−8V
to 38V
UGATE to PHASE
DC --------------------------------------------------------------------------------------------------------------------
−0.3V
to (VCC + 0.3V)
< 20ns ---------------------------------------------------------------------------------------------------------------
−5V
to 7.5V
LGATE to GND
DC --------------------------------------------------------------------------------------------------------------------
−0.3V
to (VCC + 0.3V)
< 20ns ---------------------------------------------------------------------------------------------------------------
−2.5V
to 7.5V
Power Dissipation, P
D
@ T
A
= 25°C
WQFN-12L 2x2 ---------------------------------------------------------------------------------------------------- 0.606W
Package Thermal Resistance (Note 2)
WQFN-12L 2x2,
θ
JA
---------------------------------------------------------------------------------------------- 165°C/W
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------- 260°C
Junction Temperature -------------------------------------------------------------------------------------------- 150°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
(Note 4)
Input Voltage,
V
IN
------------------------------------------------------------------------------------------------- 4.5V to 26V
Control Voltage, V
CC
---------------------------------------------------------------------------------------------
4.5V to 5.5V
Junction Temperature Range -----------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range -----------------------------------------------------------------------------------
−40°C
to 85°C
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RT8228B-05 October 2011
RT8228B
Electrical Characteristics
(V
CC
= 5V, V
IN
= 15V, V
EN
= 5V, V
MODE
= 5V, R
TON
= 500kΩ, T
A
= 25°C, unless otherwise specified)
Parameter
PWM Controller
Symbol
Test Conditions
FB forced above the regulation
point, V
EN
= 5V
V
CC
Current, V
EN
= 0V
R
TON
= 500k
R
TON
= 500k
CS pull to GND
V
CC
= 4.5V to 5.5V, DEM
V
FB
= 0.5V
V
IN
=15V, V
PHASE
= 1.25V,
V
MODE
= 0V
V
MODE
= 0V, FB = 0.45V
V
CS
= 0.5V to 2V
On the basis of 25°C
V
MODE
> V
CC
−
0.5V, PHASE
−
GND
GND
−
PHASE, V
CS
= 1V
UVP Detect, FB Falling Edge
OVP Detect, FB Rising Edge
FB forced above OV threshold
Rising Edge
Enable to current limit threshold =
50mV
From EN signal going high
Min
Typ
Max
Unit
V
CC
Quiescent Supply Current I
Q
V
CC
Shutdown Current
TON Operating Current
TON Shutdown Current
CS Shutdown Current
FB Error Comparator
Threshold Voltage
FB Input Bias Current
Output Voltage Range
On-Time
Minimum Off-Time
Current Sensing Threshold
CS Source Current
CS Source Current TC
Zero Crossing Threshold
Protection Function
Current Limit Threshold
UV Threshold
OVP Threshold
OV Fault Delay
V
CC
Power On Reset (POR)
Threshold
POR Threshold Hysteresis
Current Limit Ramp at
Soft-Start
UV Blank Time
Thermal Shutdown
T
SD
Thermal Shutdown Hysteresis
ΔT
SD
Driver On-Resistance
UGATE Driver Source
UGATE Driver Sink
LGATE Driver Source
LGATE Driver Sink
I
SHDN
--
--
--
--
--
495
−1
0.5
267
250
9
--
−10
85
60
120
--
3.7
--
--
--
--
--
0.5
--
30
--
--
500
0.1
--
334
400
10
4700
--
100
70
125
5
3.9
100
900
4.5
150
10
1.25
1
--
1
1
505
1
3.3
401
550
11
--
5
115
80
130
--
4.2
--
--
--
--
--
mA
μA
μA
μA
μA
mV
μA
V
ns
ns
μA
ppm/°C
mV
mV
%
%
μs
V
mV
μs
ms
°C
°C
BOOT
−
PHASE forced to 5V,
UGATE High State
BOOT
−
PHASE forced to 5V,
R
UGATEsk
UGATE Low State
R
LGATEsr
LGATE High State
R
LGATEsk
LGATE Low State
R
UGATEsr
--
--
--
--
2.5
1.5
2.5
0.8
5
3
5
1.5
Ω
Ω
Ω
Ω
To be continued
RT8228B-05 October 2011
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