®
RT8125F/G
High Efficiency Single Synchronous Buck PWM Controller
General Description
The RT8125F/G PWM controller provides high efficiency,
excellent transient response, and high DC output accuracy
needed for CPU core, I/O, and chipset RAM supplies in
notebook computers.
Richtek Mach Response
TM
technology is specifically
designed for providing 100ns
“instant-on”
response to
load transients while maintaining a relatively constant
switching frequency.
The RT8125F/G 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. The Buck conversion allows this device
to directly step down high voltage batteries at the highest
possible efficiency. The RT8125F/G provides an 1% high
accuracy 0.8V reference voltage with minimum 1mA
source/sink current for high accuracy output application.
Features
Richtek Mach Response
TM
Technology
1% High Accuracy 0.8V Reference
VCC Input Range : 4.5V to 13.2V
VOUT Operating Range : 0.3V to 3.3V
Power Stage Input Range : 1.5V to 24V
Fixed Operating Frequency : 300kHz
VIN Detection
LG_OCSET for Current Limit
PGOOD Indicator
Embedded Bootstrap Switch
High Side Gate Driver Pull Low Resistor (10kΩ)
Ω
Current Limit with Low Side Current Sense Scheme
Enable Function with Internal Pull High Current
OVP/UVP/OTP/Pre-OVP/Current Limit
Shutdown Current <100μA
μ
RoHS Compliant and Halogen Free
Pin Configuration
(TOP VIEW)
BOOT
UGATE
PHASE
LGATE/OCSET
VCC
GND
1
2
3
4
5
10
9
8
7
6
Applications
Generic DC-DC Power Regulator
Mother Boards and Desktop Servers
Ordering Information
RT8125F/G
Package Type
QW : WDFN-10L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
OCP Scaling During Soft-Start
F : No
G : Yes
Note :
Richtek products are :
½
11
REFOUT
REFIN
PGOOD
EN
FB
WDFN-10L 3x3
Marking Information
RT8125FGQW
LD= : Product code
LD=YM
DNN
YMDNN : Date code
RT8125GGQW
LC= : Product code
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.
½
LC=YM
DNN
YMDNN : Date code
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8125F/G-00 October 2017
www.richtek.com
61
RT8125F/G
Functional Pin Description
Pin No.
1
2
3
Pin Name
BOOT
UGATE
PHASE
Pin Function
Bootstrap supply for high side gate driver. Connect a capacitor between this
pin and the PHASE pin.
Gate drive output for the external high side MOSFET.
Switch node. 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 the low side External MOSFET. Connect a resistor
(R
OCSET
) between this pin and GND to set the output current limit level. If
R
OCSET
is not present , or the setting threshold greater than 400mV, the OC
threshold is internally present to 315mV (typ.)
Supply voltage input. It provides the power for the Buck controller, the low
side driver and the bootstrap circuit for high side driver. Bypass to GND with
a 4.7F ceramic capacitor.
V
OUT
feedback voltage input. Connect the FB to a resistive voltage divider
from V
OUT
to GND to set the output voltage from 0.3V to 3.3V
Enable control input.
Open-drain power good indicator. High impedance indicates that power is
good.
Reference input. Connect a current console to REFIN pin, and connect a
resistor between REFIN and REFOUT to tune up/down FB reference
voltage.
Reference voltage output. It provides a 1% high accuracy reference 0.8V
with 2mA source/sink ability. Bypass to GND with a maximum 6.8nF ceramic
capacitor.
Ground. The exposed pad must be soldered to a large PCB and connected
to GND for maximum power dissipation.
4
LGATE/OCSET
5
6
7
8
9
VCC
FB
EN
PGOOD
REFIN
10
11
(Exposed Pad)
REFOUT
GND
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8125F/G-00 October 2017
RT8125F/G
Functional Block Diagram
PHASE
REFIN
V
REF
+
+
-
On-time
One Shot
R
S
Q
VCC
BOOT
UGATE
PHASE
Comp
Minimum T
OFF
+
125% V
REF
FB
50% V
REF
-
-
+
OVP
Latch
UVP
Hiccup
-
LGATE/OCSET
GND
Thermal
Shutdown
90% V
REF
VCC
LDO
& POR
SS
REF
+
+
+
Gm
-
Sample
and Hold
VIN
Detection
-
+
-
V
DET
EN
REFOUT
PGOOD
Operation
The RT8125F/G is suitable for low external component count configuration with appropriate amount of Equivalent Series
Resistance (ESR) capacitor(s) at the output. The output ripple valley voltage is monitored at a feedback point voltage.
The synchronous high side MOSFET is turned on at the beginning of each cycle. After the internal one-shot timer
expires, the MOSFET is turned off. The pulse width of this one-shot is determined by the converter's input and output
voltages to keep the frequency fairly constant over the entire input voltage range. Another one-shot sets a minimum off-
time (400ns typ.).
The on-time comparator has two inputs, one is from the output voltage, the other is from the input voltage. The on-time
of the high side switch is designed to be directly proportional to the output voltage and inversely proportional to the input
voltage. The implementation results in a nearly constant switching frequency without the need of a clock generator.
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8125F/G-00 October 2017
www.richtek.com
3
RT8125F/G
Absolute Maximum Ratings
(Note 1)
−0.3V
to 15V
−0.3V
to 6.5V
−0.3V
to 40V
−0.3V
to 45V
−0.3V
to 15V
−0.3V
to 20V
VCC to GND ----------------------------------------------------------------------------------------------------------------
PGOOD, FB, EN, REFOUT, REFIN ----------------------------------------------------------------------------------
BOOT to GND --------------------------------------------------------------------------------------------------------------
<100ns -----------------------------------------------------------------------------------------------------------------------
BOOT to PHASE ----------------------------------------------------------------------------------------------------------
<100ns -----------------------------------------------------------------------------------------------------------------------
PHASE to GND
DC -----------------------------------------------------------------------------------------------------------------------------
−5V
to 25V
<100ns -----------------------------------------------------------------------------------------------------------------------
−10V
to 30V
UGATE to GND -------------------------------------------------------------------------------------------------------------
−0.3V
to 40V
<100ns -----------------------------------------------------------------------------------------------------------------------
−10V
to 45V
UGATE to PHASE
DC ----------------------------------------------------------------------------------------------------------------------------- 0.3V to 15V
<100ns -----------------------------------------------------------------------------------------------------------------------
−5V
to 20V
LGATE to GND
DC -----------------------------------------------------------------------------------------------------------------------------
−0.3V
to 15V
<100ns -----------------------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WDFN-10L 3x3 -------------------------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WDFN-10L 3x3,
θ
JA
-------------------------------------------------------------------------------------------------------
WDFN-10L 3x3,
θ
JC
-------------------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------
Junction Temperature -----------------------------------------------------------------------------------------------------
Storage Temperature Range --------------------------------------------------------------------------------------------
ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------
(Note 4)
−5V
to 20V
3.28W
30.5°C/W
7.5°C/W
260°C
150°C
−65°C
to 150°C
2kV
Recommended Operating Conditions
Input Voltage, VIN ---------------------------------------------------------------------------------------------------------
Supply Voltage, VCC -----------------------------------------------------------------------------------------------------
Junction Temperature Range --------------------------------------------------------------------------------------------
Ambient Temperature Range --------------------------------------------------------------------------------------------
1.5V to 24V
4.5V to 13.2V
−40°C
to 125°C
−40°C
to 85°C
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8125F/G-00 October 2017
RT8125F/G
Electrical Characteristics
(V
CC
= 5V, V
IN
= 15V, EN = 5V, T
A
= 25°C, unless otherwise specified)
Parameter
PWM Controller
VCC POR Threshold
V
CC
Quiescent Supply
Current
V
CC
Shutdown Current
REFOUT
(Note 5)
Symbol
Test Conditions
Rising Edge, Hysteresis = 120mV,
PWM disabled below this level
FB Forced above the regulation point,
EN = 5V, REFOUT current = 0
V
CC
current, EN = 0V
V
CC
= 4.5V to 13.2V, sink/ source
current = 2mA
Min
Typ
Max
Unit
3.9
--
--
786
--
4.2
500
--
794
--
0
--
300
--
10
0.7
4.5
1250
100
802
2
1
3.3
330
--
11
--
V
A
A
mV
mA
A
V
kHz
ns
A
ms
I
Q
I
SHDN
V
REFOUT
I
REFOUT
REFOUT Source / Sink
Current
FB Input Bias Current
REFIN Input Voltage Range
Switching Frequency
Minimum Off-Time
Current Sensing
I
OCSET
Soft-Start Time
Protection Function
Current Limit Setting
Range
Current Limit Threshold
UV Threshold
OVP Threshold
REFIN Absolute OVP
Threshold
Thermal Shutdown
VIN Detection
Threshold
Driver On-Resistance
UGATE Driver Source
UGATE Driver Sink
LGATE Driver Source
LGATE Driver Sink
Dead Time
Internal Boost Charging
Switch On-Resistance
FB = 0.8V
(Note 6)
1
0.3
270
250
9
t
SS
REFIN = 0.8V, no load
--
LGATE
R
OCSET
NC
UVP detect, FB lower than REFIN
voltage
OVP detect, FB higher than REFIN
voltage
50
--
225
225
3.35
--
315
300
300
3.5
140
--
400
--
375
375
--
--
--
mV
mV
mV
mV
V
C
V
Latch
V
DET
V
BOOT
V
PHASE
= 12V, source
current = 100mA
BOOT
PHASE = 12V, I
SINK
= 10mA
V
CC
= 12V, source current = 100mA
V
CC
= 12V, I
SINK
= 10mA
LGATE rising (PHASE = 1.5V)
UGATE rising
VCC to BOOT, 10mA
--
0.5
R
UGATEsr
R
UGATEsk
R
LGATEsr
R
LGATEsk
--
--
--
--
--
--
--
1.5
2.25
1.5
1
30
30
--
3
4
3
2
--
--
80
ns
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8125F/G-00 October 2017
www.richtek.com
5
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