®
RT6254A/B
4A, 18V, 500kHz, ACOT
TM
Step-Down Converter
General Description
The
RT6254A/B is a high-efficiency, monolithic
synchronous step-down DC-DC converter that can deliver
up to 4A output current from a 4.5V to 18V input supply.
The RT6254A/B adopts ACOT architecture to allow the
transient response to be improved and keep in constant
frequency. Cycle-by-cycle current limit provides protection
against shorted outputs and soft-start eliminates input
current surge during start-up. Fault conditions also include
output under voltage protection and thermal shutdown.
Features
4.5V to 18V Input Voltage Range
4A Output Current
Constant-on-Time Mode to Enables Fast Transient
Response
Low Output Ripple and Allows Ceramic Output
Capacitor
500kHz Switching Frequency
High Efficient Internal Power MOSFET Switch
Optimized for Lower Duty Cycle Applications
Integrated 48mΩ/25mΩ MOSFETs
Ω
Ω
Adjustable Output Voltage from 0.6V to 5V
Internal Soft-Start (1.5ms typ.)
Built-In UVP/OTP
Power Good Indicator (90%)
Input Under Voltage Lockout
TSOT23-6 (FC) and TSOT23-8 (FC) Packages
Ordering Information
RT6254A/B
Package Type
J6F : TSOT-23-6 (FC)
J8F : TSOT-23-8 (FC)
Lead Plating System
G : Green (Halogen Free and Pb Free)
UVP Option
H : Hiccup
PSM/PWM
A : PSM/PWM
B : Force-PWM
Note :
Richtek products are :
½
Applications
Set Top Box
Portable TV
Access Point Router
DSL Modem
LCD TV
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
Simplified Application Circuit
RT6254A/B
V
IN
C
IN
VIN
BOOT
C
BOOT
L
Enable
R
PGOOD
EN
PGOOD*
AGND
GND
LX
R
T
R1
R2
C
FF
C
OUT
V
OUT
FB
* : PGOOD pin is for TSOT23-8 (FC) package.
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6254A/B-02 March 2017
www.richtek.com
1
RT6254A/B
Pin Configuration
(TOP VIEW)
PGOOD
BOOT
VIN
5
4
BOOT LX
6
5
2
VIN
4
3
8
7
2
FB
EN
AGND
TSOT-23-6 (FC)
TSOT-23-8 (FC)
Marking Information
RT6254AHGJ6F
2D= : Product Code
RT6254AHGJ8F
1J= : Product Code
DNN : Date Code
2D=DNN
1J=DNN
DNN : Date Code
RT6254BHGJ6F
2C= : Product Code
RT6254BHGJ8F
1H= : Product Code
DNN : Date Code
2C=DNN
1H=DNN
DNN : Date Code
Functional Pin Description
Pin No.
TSOT-23-6 (FC)
1
--
2
3
4
5
TSOT-23-8 (FC)
1
3
2
4
5
6
Pin Name
FB
AGND
EN
GND
VIN
LX
Pin Function
Feedback voltage input. This pin is used to set the desired
output voltage via an external resistive divider.
Analog ground. This is the signal ground reference for the IC.
Enable control input. Connecting this pin to logic high can
enable the device and connecting this pin to GND can disable
the device.
System ground. This is the power return for the IC.
Power input. Supplies the power switches of the device.
Switch node. LX is the switching node that supplies power to the
output and connect the output LC filter from LX to the output
load.
Bootstrap supply for high-side gate driver. Connect a 0.1F
ceramic capacitor from LX to BOOT to power the high-side
switch.
Power good indicator. Open-drain output when the output
voltage is within 90% to 120% of regulation point.
6
--
7
8
BOOT
PGOOD
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS6254A/B-02 March 2017
GND
FB
EN GND
LX
6
3
RT6254A/B
Functional Block Diagram
TSOT-23-6 (FC)
BOOT
VIN
VIN
Reg
P
VCC
Minoff
P
VCC
UGATE
VIBIAS
V
REF
OC
UV
Control
Driver
LX
LGATE
GND
EN
VIN
On-Time
LX
P
VCC
LX
Ripple
Gen.
GND LX
EN
+
+
-
-
Comparator
FB
TSOT-23-8 (FC)
BOOT
VIN
VIN
Reg
P
VCC
Minoff
P
VCC
UGATE
VIBIAS
V
REF
OC
UV
Control
Driver
LX
LGATE
GND
EN
VIN
On-Time
LX
P
VCC
LX
Ripple
Gen.
GND LX
EN
+
+
Comparator
FB
PGOOD AGND
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6254A/B-02 March 2017
www.richtek.com
3
RT6254A/B
Operation
The RT6254A/B
is a high-efficiency, monolithic
synchronous step-down DC-DC converter that can deliver
up to 4A output current from a 4.5V to 18V input supply.
Using the ACOT
TM
control mode can reduce the output
capacitance and perform fast transient response. It can
minimize the component size without additional external
compensation network.
Current Limit
The RT6254A/B current limit is a cycle-by-cycle
“valley”
type, measuring the inductor current through the
synchronous rectifier during the off-time while the inductor
current ramps down. The current is determined by
measuring the voltage between Source and Drain of the
synchronous rectifier, adding temperature compensation
for greater accuracy. If the current exceeds the current
limit, the on-time one-shot is inhibited until it drops below
the current limit level. If the output current exceeds the
available inductor current (controlled by the current limit
mechanism), the output voltage will drop. If it drops below
the output under-voltage protection level (see next section)
the IC will stop switching to avoid excessive heat.
Hiccup Mode
The RT6254A/B use hiccup mode for UVP. When the
protection function is triggered, the IC will shut down for a
period of time and then attempt to recover automatically.
Hiccup mode allows the circuit to operate safely with low
input current and power dissipation, and then resume
normal operation as soon as the overload or short circuit
is removed.
Input Under-Voltage Lockout
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VIN is lower than the UVLO falling threshold voltage, the
device will be lockout.
Shut-Down, Start-Up and Enable (EN)
The enable input (EN) has a logic-low level. When V
EN
is
below this level the IC enters shutdown mode. When V
EN
exceeds its logic-high level the IC is fully operational.
External Bootstrap Capacitor
Connect a 0.1μF low ESR ceramic capacitor between
BOOT and LX. This bootstrap capacitor provides the gate
driver supply voltage for the high side N-MOSFET switch.
Over-Temperature Protection
The RT6254A/B includes an Over-Temperature Protection
(OTP) circuitry to prevent overheating due to excessive
power dissipation. The OTP will shut down switching
operation when the junction temperature exceeds 150°C.
Once the junction temperature cools down by
approximately 15°C, the IC will resume normal operation.
For continuous operation, provide adequate cooling so
that the junction temperature does not exceed 150°C.
UVP Protection
The RT6254A/B detects under-voltage conditions by
monitoring the feedback voltage on FB pin. When the
feedback voltage is lower than 60% of the target voltage,
the UVP comparator will go high to turn off both internal
high-side and low-side MOSFETs.
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6254A/B-02 March 2017
RT6254A/B
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------
−0.3V
to 20V
Enable Pin Voltage, EN ---------------------------------------------------------------------------------------------------
−0.3V
to 20V
Switch Node Voltage, LX --------------------------------------------------------------------------------------------------
−0.3V
to 20V
<20ns -------------------------------------------------------------------------------------------------------------------------
−5V
to 27V
BOOT to LX, V
BOOT
−
V
LX -------------------------------------------------------------------------------------------------------------------------------------------
−0.3V
to 6V
Other Pins --------------------------------------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
TSOT-23-6 (FC) -------------------------------------------------------------------------------------------------------------- 1.923W
TSOT-23-8 (FC) -------------------------------------------------------------------------------------------------------------- 1.923W
Package Thermal Resistance (Note 2)
TSOT-23-6 (FC),
θ
JA
-------------------------------------------------------------------------------------------------------- 52°C/W
TSOT-23-8 (FC),
θ
JA
-------------------------------------------------------------------------------------------------------- 52°C/W
TSOT-23-6 (FC),
θ
JC
-------------------------------------------------------------------------------------------------------- 5°C/W
TSOT-23-8 (FC),
θ
JC
-------------------------------------------------------------------------------------------------------- 5°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 Model) ----------------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage ------------------------------------------------------------------------------------------------------- 4.5V to 18V
Junction Temperature Range ---------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Supply Voltage
Symbol
Test Conditions
Min
Typ
Max
Unit
VIN Supply Input Operating
V
IN
Voltage
Vin Under-Voltage Lockout
Threshold-Rising
V
UVLO
VIN rising
4.5
3.9
--
--
4.1
0.3
18
4.3
--
V
V
V
VIN Under-Voltage Lockout
V
UVLO
Threshold-Hysteresis
Supply Current
Shutdown Current
Quiescent Current
Soft-Start
Soft-Start Time
t
SS
I
SHDN
I
Q
V
EN
= 0
I
OUT
= 0
V
FB
= V
REF
x 105% (no switching)
--
--
3
115
--
--
A
A
--
1.5
--
ms
Copyright
©
2017 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6254A/B-02 March 2017
www.richtek.com
5
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