®
RT7275/76
3A, 18V, 700kHz ACOT
TM
Synchronous Step-Down Converter
General Description
The RT7275/76 are high-performance 700kHz 3A step-
down regulators with internal power switches and
synchronous rectifiers. They feature quick transient
response using their Advanced Constant On-Time
(ACOT
TM
) control architecture that provides stable
operation with small ceramic output capacitors and without
complicated external compensation, among other benefits.
The input voltage range is from 4.5V to 18V and the output
is adjustable from 0.765V to 8V.
The proprietary ACOT
TM
control improves upon other fast-
response constant on-time architectures, achieving nearly
constant switching frequency over line, load, and output
voltage ranges. Since there is no internal clock, response
to transients is nearly instantaneous and inductor current
can ramp quickly to maintain output regulation without
large bulk output capacitance. The RT7275/76 are stable
with and optimized for ceramic output capacitors.
With internal 90mΩ switches and 60mΩ synchronous
rectifiers, the RT7275/76 display excellent efficiency and
good behavior across a range of applications, especially
for low output voltages and low duty cycles. Cycle-by-
cycle current limit, input under-voltage lock-out,
externally-adjustable soft-start, output under- and over-
voltage protection, and thermal shutdown provide safe and
smooth operation in all operating conditions.
The RT7275 and RT7276 are each available in WDFN-10L
3x3 and PTSSOP-14 packages, with exposed thermal
pads.
Features
Fast Transient Response
Steady 700kHz Switching Frequency
At all Load Currents (RT7275)
Discontinuous Operating Mode at Light Load
(RT7276)
3A Output Current
Advanced Constant On-Time (ACOT
TM
) Control
Optimized for Ceramic Output Capacitors
4.5V to 18V Input Voltage Range
Internal 90mΩ Switch and 60mΩ Synchronous
Ω
Ω
Rectifier
0.765V to 8V Adjustable Output Voltage
Externally-adjustable, Pre-biased Compatible Soft-
Start
Cycle-by-Cycle Current Limit
Optional Output Discharge Function (PTSSOP-14
Only)
Output Over- and Under-voltage Shut-down
Applications
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
Not Recommended for Sink/Source Applications
Fast-Transient Response
RT7275
Simplified Application Circuit
V
IN
Input Signal
Power Good
RT7275/76
VIN
SW
VINR
EN
BOOT
FB
V
OUT
V
OUT
(20mV/Div)
PGOOD
VOUT
PVCC
SS
PGND GND
I
OUT
(2A/Div)
V
OUT
= 12V, V
OUT
= 1.05V, I
OUT
= 0 to 3A
Time (100μs/Div)
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7275/76-00
January 2013
www.richtek.com
1
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
