Design
Tools
®
RT7294B
2.5A, 18V, 500kHz ACOT
TM
Synchronous Step-Down Converter
General Description
The RT7294B is a synchronous step-down converter with
Advanced Constant On-Time (ACOT
TM
) mode control. The
ACOT
TM
provides a very fast transient response with few
external components. The low impedance internal
MOSFET supports high efficiency operation with wide input
voltage range from 4.3V to 18V. The proprietary circuit of
the RT7294B enables to support all ceramic capacitors.
The output voltage can be adjusted between 0.6V and 8V.
Features
4.3V to 18V Input Voltage Range
2.5A Output Current
Advanced Constant On-Time Control
Fast Transient Response
Support All Ceramic Capacitors
Up to 95% Efficiency
500kHz Switching Frequency
Adjustable Output Voltage from 0.6V to 8V
Cycle-by-Cycle Current Limit
Input Under-Voltage Lockout
Thermal Shutdown
Power Saving Mode for High Efficiency at Light
Load
Ordering Information
RT7294B
Package Type
J6F : TSOT-23-6 (FC)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Applications
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
Pin Configuration
(TOP VIEW)
SW VIN EN
6
5
2
4
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Marking Information
00= : Product Code
00=DNN
3
DNN : Date Code
BOOT GND FB
TSOT-23-6 (FC)
Simplified Application Circuit
RT7294B
V
IN
VIN
BOOT
SW
Enable
EN
GND
FB
V
OUT
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7294B-07 August 2018
www.richtek.com
1
RT7294B
Functional Pin Description
Pin No.
1
2
3
4
5
6
Pin Name
BOOT
GND
FB
EN
VIN
SW
Pin Function
Bootstrap supply for high-side gate driver. Connect a 0.1F ceramic capacitor
between the BOOT and SW pins.
Power ground.
Feedback voltage input. The pin is used to set the output voltage of the converter
via a resistive divider. The converter regulates V
FB
to 0.6V
Enable control input. Connect EN to a logic-high voltage to enable the IC or to a
logic-low voltage to disable. Do not leave this high impedance input unconnected.
Power input. The input voltage range is from 4.3V to 18V. Must bypass with a
suitable large ceramic capacitor at this pin.
Switch node. Connect to external L-C filter.
Functional Block Diagram
BOOT
V
IN
Reg
VIBIAS
PVCC
V
REF
Min off
PVCC
UGATE
Control
UV & OV
PVCC
SW
Ripple
Gen.
+
-
-
Comparator
EN
GND SW
V
IN
On-Time
SW
Driver
LGATE
GND
SW
VIN
OC
FB
EN
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7294B-07 August 2018
RT7294B
Operation
The RT7294B is a synchronous step-down converter with
advanced constant on-time control mode. Using the ACOT
control mode can reduce the output capacitance and fast
transient response. It can minimize the component size
without additional external compensation network.
Soft-Start (SS)
The RT7294B provides an internal soft-start feature for
inrush control. At power up, the internal capacitor is
charged by an internal current source to generate a soft-
start ramp voltage as a reference voltage to the internal
comparator. The device will initiate switching and the
output voltage will smoothly ramp up to its targeted
regulation voltage only after this ramp voltage is greater
than the feedback voltage V
FB
to ensure the converters
have a smooth start-up. The output voltage starts to rise
in 0.85ms from EN rising, and the soft-start ramp-up time
(V
FB
from 0V to 0.6V) is 0.8ms.
VIN = 12V
VIN
until the fault condition is cleared. Hiccup mode allows
the circuit to operate safely with low input current and
power dissipation, and then resume normal operation as
soon as the over-load or short-circuit condition is removed.
Abnormal case
detected (UV) t
HICCUP_ON
= 1.5ms
VOUT
Resume normal
operation
Fault
condition
t
HICCUP_OFF
= 5ms removed
t
0.8ms
SW
t
UVLO Protection
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.
Thermal Shutdown
EN
0.85ms
0.8ms
VOUT
When the junction temperature exceeds the OTP
threshold value, the IC will shut down the switching
operation. Once the junction temperature cools down and
is lower than the OTP lower threshold, the converter will
autocratically resume switching.
Output Under-Voltage Protection and Hiccup Mode
The RT7294B includes output under-voltage protection
(UVP) against over-load or short-circuited condition by
constantly monitoring the feedback voltage V
FB
. If V
FB
drops below the under-voltage protection trip threshold
(typically 75% of the internal feedback reference voltage),
the UV comparator will go high to turn off both the internal
high-side and low-side MOSFET switches.
If the output under-voltage condition continues for a period
of time, the RT7294B will enter output under-voltage
protection with hiccup mode. During hiccup mode, the IC
will shut down for t
HICCUP_OFF
(5ms), and then attempt to
recover automatically for t
HICCUP_ON
(1.5ms). Upon
completion of the soft-start sequence, if the fault condition
is removed, the converter will resume normal operation;
otherwise, such cycle for auto-recovery will be repeated
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7294B-07 August 2018
www.richtek.com
3
RT7294B
Absolute Maximum Ratings
(Note 1)
VIN to GND -----------------------------------------------------------------------------------------------------
−0.3V
to 20V
SW to GND ----------------------------------------------------------------------------------------------------
−0.3V
to (V
IN
+ 0.3V)
<10ns -----------------------------------------------------------------------------------------------------------
−5V
to 25V
BOOT to GND ------------------------------------------------------------------------------------------------- (V
SW
−
0.3V) to (V
SW
+ 6V)
Other Pins ------------------------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
TSOT-23-6 (FC) ----------------------------------------------------------------------------------------------- 1.429W
Package Thermal Resistance (Note 2)
TSOT-23-6 (FC),
θ
JA
------------------------------------------------------------------------------------------ 70°C/W
TSOT-23-6 (FC),
θ
JC
----------------------------------------------------------------------------------------- 15°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 Model) --------------------------------------------------------------------------------- 2kV
(Note 4)
Recommended Operating Conditions
Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4.3V 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
Shutdown Current
Quiescent Current
Switch-On
Resistance
Current Limit
Oscillator Frequency
Maximum Duty Cycle
Minimum On-Time
Feedback Threshold Voltage
EN Input Threshold
Logic-High
Logic-Low
High-Side
Low-Side
Symbol
I
SHDN
I
Q
R
DS(ON)_H
R
DS(ON)_L
I
LIM
f
SW
D
MAX
t
ON
V
FB
V
EN_H
V
EN_L
V
UVLO
Test Conditions
V
EN
= 0V
V
EN
= 2V, V
FB
= 1V
V
BOOTSW
= 4.8V
V
IN
= 5V
Valley current
Min
--
--
--
--
2.7
--
--
--
Typ
--
0.5
150
90
3.4
500
90
60
600
1.29
1.03
3.9
340
800
160
Max
4
--
--
--
4
--
--
--
609
1.39
1.13
4.25
--
--
--
Unit
A
mA
m
A
kHz
%
ns
mV
V
V
mV
s
C
In CCM mode
591
1.19
0.93
VIN Under-Voltage Lockout
Threshold
VIN Under-Voltage Lockout
Threshold Hysteresis
Soft-Start Time
Thermal Shutdown Threshold
VIN rising
3.55
--
t
SS
T
SD
--
--
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7294B-07 August 2018
RT7294B
Parameter
Thermal Shutdown Hysteresis
V
OUT
Discharge Resistance
Symbol
T
SD
R
DISCHG
EN = 0V, V
OUT
= 0.5V
Test Conditions
Min
--
--
Typ
20
50
Max
--
100
Unit
C
Note 1.
Stresses beyond those listed under
“Absolute
Maximum Ratings” June cause permanent damage to the device.
These are stress ratings only, and functional operation of the device at these or any other conditions beyond those
indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating
conditions June affect device reliability.
Note 2.
θ
JA
is measured at T
A
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
θ
JC
is
measured at the top of the package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7294B-07 August 2018
www.richtek.com
5
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