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dc2178af

DEMO MANUAL DC2178A

with an input voltage of 4.2V. For full performance in

12V cold crank applications, a logic-level rated MOSFET

is necessary for Q1.

Optional Components

is stuffed with 2.2μF), and for optional timer capacitance

at CTMR2 (CTMR1 is stuffed with 10μF). C1B and CTMR2

are found on the bottom of the board.

An optional GATE pin clamp (D6) is also located on the

bottomoftheboard.Thisclampisnecessaryinapplications

where a large value gate capacitor (C2 ≥ 100nF) is used.

A 15V Zener is recommended for D6, to safely discharge

C2 during a hard short circuit.

Extra Holes

Five through-hole pads are included for the purpose of

attaching an off-board power stage comprising a MOS-

FET, gate suppression resistor, sense resistor and output

reservoir capacitor in high current applications, where the

components and current levels are not compatible with

the layout of DC2178A. The pads are labeled on the bot-

tom of the board and noted on the schematic as INPUT,

OUT, GATE, SNS and GND. Remove Q1 and RSNS. Make

short, direct connections between the through-hole pads

and the external components, and use SNS and OUT to

make Kelvin connections to the sense resistor. Depending

on the setup and MOSFET used, a snubber may be needed

between the MOSFET drain and the ground side of the

output reservoir capacitor, or between the MOSFET drain

and source terminals to suppress parasitic oscillations.

Small Turrets

No connection to any of the small turrets is necessary

to make the board operate—the LTC4380 defaults to the

ON state.

ON is pulled high internally. If this turret is left open, the

board will turn on when power is applied. Short this turret

to ground to turn off the LTC4380, or pulse low for at least

100μs to restart the LTC4380-1 (DC2178A-A) after a fault.

FLT pulls low when the LTC4380 faults off from an overcur-

rent or overvoltage condition. It is reset by pulling the ON

pin low for at least 100μs in the LTC4380-1 (DC2178A-A),

orafteracooldownintervalintheLTC4380-2(DC2178A-B).

FLT can sink up to 3mA.

Jumpers

Jumper JP1 sets the state of the SEL pin to select between

a 27V output clamp (SEL grounded) or a 45V output clamp

(SEL connected to OUT). The corresponding clamp volt-

age at the GATE pin is about 5V higher than these values.

Jumper JP2 disables the output LED (DLED) to facilitate

measurement of the LTC4380’s operating current.

Basic Test Setup

DANGER! High voltage testing shall be performed by

qualified personnel only. As a safety precaution at least

two people shall be present during high voltage testing.

Set the jumper, JP1, for 12V or 24V/48V operation, con-

nect a power supply to the input, and connect a load to

the output as shown in Figure 1. The circuit will turn on

automatically when power is applied, and the presence of

output power is indicated by the output LED.

To perform surge testing, add a diode (such as a 1N4004)

inserieswiththepowersupply.Couplethesurgegenerator

through a second diode to the input to test the clamping

action of DC2178A. The diodes protect the power supply

and surge generator against backfeeding.

To measure the operating current, disable the output LED

using JP2, and disconnect the load.

operating characteristics