LM2642 Two-Phase Synchronous Step-Down Switching Controller
May 2003
LM2642
Two-Phase Synchronous Step-Down Switching
Controller
General Description
The LM2642 consists of two current mode synchronous
buck regulator controllers with a switching frequency of
300kHz.
The two switching regulator controllers operate 180˚ out of
phase. This feature reduces the input ripple RMS current,
thereby significantly reducing the required input capacitance.
The two switching regulator outputs can also be paralleled to
operate as a dual-phase single output regulator.
The output of each channel can be independently adjusted
from 1.3 to V
IN
•
maximum duty cycle. An internal 5V rail is
also available externally for driving bootstrap circuitry.
Current-mode feedback control assures excellent line and
load regulation and a wide loop bandwidth for excellent
response to fast load transients. Current is sensed across
either the Vds of the top FET or across an external current-
sense resistor connected in series with the drain of the top
FET. Current limit is independently adjustable for each chan-
nel.
The LM2642 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance. This
makes the soft-start behavior more predictable and control-
lable than traditional soft-start circuits.
A PGOOD1 pin is provided to monitor the dc output of
channel 1. Over-voltage protection is available for both out-
puts. A UV-Delay pin is also available to allow delayed shut
off time for the IC during an output under-voltage event.
Features
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
Two synchronous buck regulators
180˚ out of phase operation
4.5V to 30V input range
Power good function monitors Ch.1
37µA Shutdown current
0.04% (typical) line and load regulation error
Current mode control with or without a sense resistor
Independent enable/soft-start pins allow simple
sequential startup configuration.
Configurable for single output parallel operation. (See
Adjustable cycle-by-cycle current limit
Input under-voltage lockout
Output over-voltage latch protection
Output under-voltage protection with delay
Thermal shutdown
Self discharge of output capacitors when the regulator is
OFF
TSSOP package
Applications
n
n
n
n
Embedded computer systems
High end gaming systems
Set-top boxes
WebPAD
Block Diagram
20046201
© 2003 National Semiconductor Corporation
DS200462
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
