RT8129A
High Efficiency Single Synchronous Buck PWM Controller
General Description
The RT8129A is a high efficiency single phase
synchronous buck controller with 5V/12V supply
voltage. The RT8129A integrates a Constant-On-Time
(COT) PWM controller and a MOSFET drivers with
internal bootstrap diodes, which is specifically designed
to improve converter efficiency at light load condition.
At light load condition, it automatically operates in the
diode emulation mode to reduce switching frequency
and improve conversion efficiency.
Other features include power good indication,
enable/disable control and internal soft-start function.
The RT8129A also provide protection functions
including Over Voltage Protection (OVP), Under
Voltage Protection (UVP), current limit and thermal
shutdown.
This device uses lossless low-side MOSFET R
DS(ON)
current sense technique for current limit with adjustable
threshold set by connecting a resistor between the
LGATE/OCSET and GND.
With
above
functions,
the
RT8129A
provides
5N=YM
DNN
Features
Wide Input Voltage Range : 2.5V to 25V
High Light Load Efficiency
Integrated High Driving Capability N-MOSFET
Gate
Drivers and Embedded Switching Boot Diode
Single IC Supply Voltage : 4.5V to 13.2V
Power-Good Indicator
Enable/Disable Control
Internal Soft-Start
Programmable Current Limit Threshold
Under Voltage Protection
Over Voltage Protection
Thermal Shutdown
Applications
Motherboard, Memory/Chip-set Power
Graphic Card, GPU/Memory Core Power
Low Voltage, High Current DC/DC Regulator
Marking Information
5N= : Product Code
YMDNN : Date Code
customers a cost-effective solution for high efficiency
power conversion. The RT8129A is available in the
WDFN-10L 3x3 package.
Simplified Application Circuit
V
IN
RT8129A
V
CC
VCC
BOOT
UGATE
PHASE
V
PGOOD
PGOOD
EN
LGATE/
OCSET
V
OUT
Enable
FB
GND
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8129A-01
October
2015
www.richtek.com
1
RT8129A
Ordering Information
RT8129A
Package Type
QW : WDFN-10L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
Pin Configurations
(TOP VIEW)
BOOT
PHASE
UGATE
LGATE/OCSET
GND
1
2
3
4
5
10
9
8
7
6
11
PGOOD
NC
FB
EN
VCC
WDFN-10L 3x3
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Functional Pin Description
Pin No.
Pin Name
Pin Function
Bootstrap Supply for High Side Gate Driver. Connect this pin to a power
source VCC through a bootstrap diode, and connect a 0.1F or greater
ceramic capacitor from this pin to the PHASE pin to supply the power for
high side gate driver.
Switch Node. Connect this pin to the switching node of Buck converter.
Connect this pin to the Source of high-side MOSFET together with the Drain
of low-side MOSFET and the inductor. The PHASE voltage is sensed for
zero current detection and over current protection when low side MOSFET
is on.
High Side MOSFET Gate Driver Output. This pin provides the gate drive for
the converter's high-side MOSFET. Connect this pin to the Gate of high-side
MOSFET.
1
BOOT
2
PHASE
3
UGATE
4
Low Side MOSFET Gate Driver Output. Connect this pin to the Gate of low
side MOSFET. This pin is also used for current limit threshold setting.
LGATE/OCSET
Connect a resistor (ROCSET) from this pin to the GND pin to set the current
limit threshold.
Ground. The Exposed Pad must be soldered to a large PCB and connected
to GND for maximum power dissipation.
Supply Voltage Input. It is recommended to connect a 4.7F ceramic
capacitor from this pin to the GND pin. VCC also powers the low side gate
driver.
Enable Control Input. Drive EN higher than 2V to turn on the controller,
lower than 0.8V to turn it off. If the EN pin is open, it will be pulled to high by
internal circuit.
This pin is used for output voltage feedback input and it is also monitored for
power good indication, over voltage and under voltage protections.
Connect this pin to the converter output through voltage divider resistors for
output voltage regulation.
No Internal Connection.
Power Good Indication Output. This pin provides an open drain output.
Connect this pin to a voltage source through a pull up resistor. The PGOOD
voltage goes high to indicate the output voltage is in regulation. This pin can
be left open if the power good indication function is not used.
5,
GND
11 (Exposed Pad)
6
VCC
7
EN
8
FB
9
NC
10
PGOOD
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8129A-01
GND
October
2015
RT8129A
Function Block Diagram
PHASE
Trigger
T
ON
Generator
1-Shot
V
REF
BOOT
+
-
COMP
R
S
Min T
OFF
1-Shot
Trigger
Q
UGATE
PHASE
VCC
+
OV
125% V
REF
FB
75% V
REF
PGOOD
PGOOD
Monitor
±10% V
REF
LDO&
POR
-
-
+
Latch
S1
Q
Latch
S1
Q
Thermal
Shutdown
UV
LGATE/OCSET
GND
ASM
Sample
and Hold
10µA
+
gm
-
+
VCC
EN
SS
REF
V
REF
-
Operation
The RT8129A integrates a Constant-On-Time (COT)
PWM controller and MOSFET driver so that the
external circuit is easily designed and the components
are reduced.
The controller provides the PWM signal which relies on
the FB voltage comparing with internal reference
voltage. The synchronous UGATE driver is turned on at
the beginning of each cycle. After the internal one-shot
timer expires, the UGATE driver will be turned off. The
pulse width of this one-shot is determined by the
controller's input voltage and the output voltage to keep
the frequency fairly constant over the input voltage and
output voltage range. Another one-shot sets a
minimum off-time.
Enable
The RT8129A remains in shutdown if the EN pin
voltage is lower than 0.8V. When the EN pin voltage
rises above the2V, the RT8129A will begin a new
initialization and soft-start cycle.
PGOOD
The power good output is an open-drain architecture,
and it requires a pull-up resistor. During soft-start
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
process, PGOOD is actively held low and is allowed to
be pulled high after soft start process is completed and
no protection occur. In addition, if the FB pin voltage is
higher than 110% of VREF or lower than 90% of VREF
during operation, PGOOD will be pulled low
immediately.
Soft-Start
An internal current source charges an internal capacitor
to build the soft-start ramp voltage.
The output voltage will track the internal ramp voltage
during soft-start interval. The typical soft-start time is
2ms.
Current Limit
The current limit circuit employs a unique “valley”
current sensing algorithm. If the magnitude of the
current sense signal at PHASE is above the current
limit threshold, the PWM is not allowed to initiate a new
cycle. Thus, the current to the load exceeds the
average output inductor current, the output voltage falls
and eventually crosses the under-voltage protection
threshold, inducing IC shutdown.
is a registered trademark of Richtek Technology Corporation.
DS8129A-01
October
2015
www.richtek.com
3
RT8129A
Over Voltage Protection (OVP)
The FB voltage can be continuously monitored for over
voltage protection. When the FB voltage exceeds
125% of the reference voltage, UGATE goes low and
LGATE is forced high. The controller is latched until
VCC is re-supplied and exceeds the POR rising
threshold voltage.
There is a 5s delay built into the under voltage
protection circuit to prevent false transitions.
Under Voltage Protection (UVP)
The output voltage can be continuously monitored for
under voltage protection. When the FB voltage is less
than 75% of the reference voltage, under voltage
protection is triggered and then both UGATE and
LGATE gate drivers are forced low. The controller is
latched until VCC or EN pin voltage is re-supplied and
exceeds the POR rising threshold voltage.
There is a 3s delay built into the under voltage
protection circuit to prevent false transitions.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8129A-01
October
2015
RT8129A
Absolute Maximum Ratings
(Note 1)
VCC to GND ------------------------------------------------------------------------------------------------------------
0.3V
to 15V
Other Pins ---------------------------------------------------------------------------------------------------------------
0.3V
to 6.5V
BOOT to PHASE
DC--------------------------------------------------------------------------------------------------------------------------0.3V to 15V
<100ns --------------------------------------------------------------------------------------------------------------------0.3V to 20V
PHASE to GND
DC-------------------------------------------------------------------------------------------------------------------------
5V
to 25V
<100ns -------------------------------------------------------------------------------------------------------------------
10V
to 30V
BOOT to GND
DC-------------------------------------------------------------------------------------------------------------------------
0.3V
to 40V
<100ns -------------------------------------------------------------------------------------------------------------------
0.3V
to 45V
UGATE to GND
DC-------------------------------------------------------------------------------------------------------------------------
0.3V
to 40V
<100ns -------------------------------------------------------------------------------------------------------------------
10V
to 45V
UGATE to PHASE
DC-------------------------------------------------------------------------------------------------------------------------
0.3V
to 15V
<40ns ---------------------------------------------------------------------------------------------------------------------
5V
to 20V
LGATE to GND
DC-------------------------------------------------------------------------------------------------------------------------
0.3V
to 15V
<100ns -------------------------------------------------------------------------------------------------------------------
5V
to 20V
Power Dissipation, P
D
@ T
A
= 25C
WDFN-10L 3x3 --------------------------------------------------------------------------------------------------------
3.27W
Package Thermal Resistance
(Note 2)
WDFN-10L 3x3,
JA
--------------------------------------------------------------------------------------------------
30.5C/W
WDFN-10L 3x3,
JC
--------------------------------------------------------------------------------------------------
7.5C/W
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------
260C
Junction Temperature ------------------------------------------------------------------------------------------------
150C
Storage Temperature Range ---------------------------------------------------------------------------------------
65C
to 150C
ESD Susceptibility
(Note 3)
HBM (Human Body Model) -----------------------------------------------------------------------------------------
2kV
(Note 4)
Recommended Operating Conditions
Power Input Voltage, VIN -------------------------------------------------------------------------------------------
2.5V
to 25V
Control Voltage, VCC ------------------------------------------------------------------------------------------------
4.5V
to 13.2V
Ambient Temperature Range---------------------------------------------------------------------------------------
40C
to 85C
Junction Temperature Range --------------------------------------------------------------------------------------
40C
to 125C
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8129A-01
October
2015
www.richtek.com
5
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