RT7235/36/39/40
®
DS7235/36/39/40-08 January 2017 www.richtek.com
1
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General Description
The RT7235/36/39/40 is a synchronous step-down DC/
DC converter with Advanced Constant On-Time (ACOT
TM
)
mode control. It achieves high power density to deliver up
to 5A output current from a 4.5V to 18V input supply. The
proprietary ACOT
TM
mode offers an optimal transient
response over a wide range of loads and all kinds of ceramic
capacitors, which allows the device to adopt very low ESR
output capacitor for ensuring performance stabilization. In
addition, RT7235/36/39/40 keeps an excellent constant
switching frequency under line and load variation and the
integrated synchronous power switches with the ACOT
TM
mode operation provides high efficiency in whole output
current load range. Cycle-by-cycle current limit provides
an accurate protection by a valley detection of low side
MOSFET and external soft-start setting eliminates input
current surge during startup. Protection functions include
thermal shutdown for RT7235/36/39/40, output Under
Voltage Protection (UVP) / Over Voltage Protection (OVP)
for RT7235/36. When the UVP/OVP is triggered, the device
will enter latch mode for TSSOP-14 (Exposed Pad), and
hiccup mode for WDFN-10L 3x3.
The RT7235/36 are available in TSSOP-14 (Exposed Pad)
and WDFN-10L 3x3 packages, and the RT7235 is operated
in forced continuous conduction mode.
The RT7239/40 are available in the SOP-8 (Exposed Pad)
package, and the RT7239 is operated in forced continuous
conduction mode.
Features
ACOT
TM
Mode Enables Fast Transient Response
4.5V to 18V Input Voltage Range
5A Output Current
35m
ΩΩ
ΩΩ
Ω Internal Low Site N-MOSFET
Advanced Constant On-Time Control
Support All Ceramic Capacitors
Up to 95% Efficiency
650kHz Switching Frequency at all Load Current
(RT7235, RT7239)
Discontinuous Operating Mode at Light Load
(RT7236, RT7240)
Adjustable Output Voltage from 0.765V to 8V
Adjustable Soft-Start
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Thermal Shutdown
RoHS Compliant and Halogen Free
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
Simplified Application Circuit
5A, 18V, 650kHz, ACOT
TM
Synchronous Step-Down Converter
PGOOD*
RT7235/36/39/40
VREG5
FB
VCC*
V
IN
BOOT
SW
SS
V
OUT
VIN
GND*
PGND
EN
Enable
Power GOOD
VS*
* : VCC pin for TSSOP-14 (Exposed Pad) only.
VS pin for TSSOP-14 (Exposed Pad) only.
GND pin for TSSOP-14 (Exposed Pad) only.
PGOOD pin for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only.
