High Voltage, Dual Synchronous Buck Converter with
The LM5642 series consists of two current mode syn-
chronous buck regulator controllers operating 180° out of
phase with each other at a normal switching frequency of
200kHz for the LM5642 and at 375kHz for the LM5642X.
Out of phase operation reduces the input RMS ripple current,
thereby significantly reducing the required input capacitance.
The switching frequency can be synchronized to an external
clock between 150kHz and 250kHz for the LM5642 and be-
tween 200 kHz and 500 kHz for the LM5642X. 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 1.3V to 90% of Vin. An internal 5V rail is also available
externally for driving bootstrap circuitry.
Current-mode feedback control assures excellent line and
load regulation and wide loop bandwidth for excellent re-
sponse 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.
The LM5642 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance making the
soft-start behavior more predictable and controllable than tra-
ditional soft-start circuits.
Over-voltage protection is available for both outputs. A UV-
Delay pin is also available to allow delayed shut off time for
the IC during an output under-voltage event.
Typical Application Circuit
© 2007 National Semiconductor Corporation
Two synchronous buck regulators
180° out of phase operation
200kHz fixed nominal frequency: LM5642
375kHz fixed nominal frequency: LM5642X
Synchronizable switching frequency from 150kHz to
250kHz for the LM5642 and 200kHz to 500kHz for the
4.5V to 36V input range
50µA Shutdown current
Adjustable output from 1.3V to 90% of Vin
0.04% (typical) line and load regulation accuracy
Current mode control with or without a sense resistor
Independent enable/soft-start pins allow simple sequential
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
Self discharge of output capacitors when the regulator is
TSSOP and eTSSOP (Exposed PAD) packages
Embedded Computer Systems
Point Of Load Power Architectures