LINEAR dn378f Data Sheet

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Monolithic Step-Down Regulator Withstands The Rigors of Automotive Environments and Consumes Only 100µA of Quiescent Current – Design Note 378 Rich Philpott Introduction External synchronization can be implemented by driving

Automobile electronic systems place high demands on the SYNC pin with a logic-level input. The SYNC pin also today’s DC/DC converters. They must be able to precisely doubles as Burst Mode defeat for applications where regulate an output voltage in the face of wide temperature lower output ripple is desired over light load effi ciency. A and input voltage ranges—including load dump transients single capacitor provides soft-start capability which limits in excess of 60V and cold crank voltage drops to 4V. The inrush current and output voltage overshoot during startup converter must also be able to minimize battery drain in and recovery from brown-out situations. The LT3437 is always-on systems by maintaining high effi ciency over a available in either a low profi le 3mm × 3mm 10-pin DFN broad load current range. Similar demands are made by or 16-pin TSSOP package both with an exposed pad many 48V nonisolated telecom applications, 40V Fire Wire leadframe for low thermal resistance.

peripherals and battery-powered applications with auto

Brutal Input Transients

plug adaptors. The LT3437’s best in class performance

Figure 2 shows the LT3437’s reaction to the severe input

meets all of these requirements in a small thermally

transients that are possible in an automotive environ-

enhanced 3mm × 3mm DFN package.

ment. Here, the input voltage rises from a nominal 12V

Features of the LT3437 to 80V in a 100ms load dump pulse, then drops to 4V in

The LT®3437 is a 200k Hz fi xed frequency, 500m A a 150ms cold crank pulse. The 200k Hz fi xed frequency monolithic buck switching regulator. Its 3.3V to 80V and current mode topology of the LT3437 allow it to take input voltage range makes the LT3437 ideal for harsh it all in its stride—response to the input transients are automotive environments. Micropower bias current and less than 1% of the regulated voltage.

Burst Mode® operation help to maintain high effi ciency

The fuzziness seen on the output voltage is due to the

over the entire load range and result in a no load quies-

ESR of the output capacitor and the change in inductor

cent current of only 100µA for the circuit in Figure 1. The

current ripple as the input voltage transitions between

LT3437 has an undervoltage lockout and a shutdown pin

, LTC, LT and Burst Mode are registered trademarks of Linear Technology

with an accurate threshold for a <1µA quiescent current

Corporation. All other trademarks are the property of their respective owners.

shutdown mode.

VIN BOOST 3.3V

3.75V TO 80V*

2.2µF 0.1µF 100µH 250m A BAS21

100V SHDN LOAD DUMP

CER LT3437 0.1µF

10MQ100N

CSSVC VIN 20V/DIV

VBIAS

24k COLD CRANK

SYNC FB 0V

6.3V 100k TANT

GND VOUT 20m V/DIV AC COUPLED

*FOR INPUT VOLTAGES ABOVE 60V SOME RESTRICTIONS MAY APPLY. DN378 F01

SEE ABSOLUTE MAXIMUM RATINGS IN DATA SHEET DN378 F02

50ms/DIV

Figure 1. 14V to 3.3V Step-Down Converter Figure 2. Output Voltage Response to Load with 100µA No Load Quiescent Current Dump and Cold Crank Input Transients