January 20, 2009
LM20333A
36V, 3A Synchronous Buck Regulator with Frequency
Synchronization
General Description
The LM20333A is a full featured synchronous buck regulator
capable of delivering up to 3A of load current. The current
mode control loop is externally compensated with only two
components, offering both high performance and ease of use.
The device is optimized to work over the input voltage range
of 4.5V to 36V making it well suited for high voltage systems.
Features
4.5V to 36V input voltage range
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3A output current, 5.2A peak current
130 mΩ/110 mΩ integrated power MOSFETs
94% peak efficiency with synchronous rectification
1.0% feedback voltage accuracy
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Current mode control, selectable compensation
Oscillator synchronization from 250kHz to 1.5MHz
Adjustable output voltage down to 0.8V
Compatible with pre-biased loads
The device features internal Over Voltage Protection (OVP)
and Over Current Protection (OCP) circuits for increased sys-
tem reliability. A precision Enable pin and integrated UVLO
allows the turn on of the device to be tightly controlled and
sequenced. Startup inrush currents are limited by both an in-
ternally fixed and externally adjustable soft-start circuit. Fault
detection and supply sequencing are possible with the inte-
grated power good (PGOOD) circuit.
Programmable soft-start with external capacitor
Precision enable pin with hysteresis
OVP, UVLO inputs and PGOOD output
The LM20333A is designed to work well in multi-rail power
supply architectures. The output voltage of the device can be
configured to track a higher voltage rail using the SS/TRK pin.
If the output of the LM20333A is pre-biased at startup it will
not sink current to pull the output low until the internal soft-
start ramp exceeds the voltage at the feedback pin.
Internally protected with peak current limit, thermal
shutdown and restart
Accurate current limit minimizes inductor size
Non-linear current mode slope compensation
eTSSOP-20 exposed pad package
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The switching frequency of the LM20333A can be synchro-
nized to an external clock by use of the SYNC pin. The SYNC
pin is capable of synchronizing to input signals ranging from
250 kHz to 1.5 MHz.
Simple to design, high efficiency point of load regulation
The LM20333A is offered in an exposed pad 20-pin eTSSOP
package that can be soldered to the PCB, eliminating the
need for bulky heatsinks.
High Performance DSPs, FPGAs, ASICs and
Microprocessors
Communications Infrastructure, Automotive
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Simplified Application Circuit
30077401
®
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