LINEAR dn402 Data Sheet User Guide

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Electronic Circuit Breaker in Small DFN Package Eliminates Sense Resistor – Design Note 402 SH Lim Introduction Overvoltage Protection Traditionally, an Electronic Circuit Breaker (ECB) com-

The LTC4213 can provide load overvoltage protection

prises a MOSFET, a MOSFET controller and a current sense

(OVP) above the bias supply. When VSENSEP > VCC + 0.7V

resistor. The LTC®4213 does away with the sense resistor

for 65µs, an internal OVP circuit activates with the GATE

by using the RDS(ON) of the external MOSFET. The result

pin pulling low and the external MOSFET turning off. The

is a simple, small solution that offers a signifi cant low

OVP circuit protects the system from an incorrect plug-in

insertion loss advantage at low operating load voltage.

event where the VIN load supply is much higher than the

The LTC4213 features two circuit breaking responses to

VCC bias voltage.

varying overload conditions with three selectable trip

thresholds and a high side drive for an external N-chan- Typical Electronic Circuit Breaker (ECB) nel MOSFET switch. Application Overcurrent Protection Figure 1 shows the LTC4213 in a dual supply ECB ap- plication. An input bypass capacitor is recommended to

The SENSEP and SENSEN pins monitor the load cur-

prevent transient spikes when the VIN supply powers-up

rent via the RDS(ON) of the external MOSFET and serve

or the ECB responds to overcurrent conditions. Figure 2

as inputs to two internal comparators—SLOWCOMP

shows a normal power-up sequence. The LTC4213 exits

and FASTCOMP—with trip points at VCB and VCB(FAST),

reset mode once the VCC pin is above the internal under

respectively. The circuit breaker trips when an overcur-

voltage lockout threshold and the ON pin rises above

rent fault causes a substantial voltage drop across the

0.8V (see trace 1 in Figure 2). After an internal 60µs de-

MOSFET. An overload current exceeding VCB/RDS(ON)

bounce cycle, the GATE pin capacitance is charged up

causes SLOWCOMP to trip the circuit breaker after a 16µs

from ground by an internal 100µA current source (see

delay. In the event of a severe overload or short-circuit

trace 2). As the GATE pin and the gate of MOSFET charges

current exceeding VCB(FAST)/RDS(ON), the FASTCOMP

up, the external MOSFET turns on when VGATE exceeds

trips the circuit breaker within 1µs, protecting both the

the MOSFET’s threshold. The circuit breaker is armed

MOSFET and the load.

when VGATE exceeds ΔVGSARM, a voltage at which the Both of the comparators have a common mode input external MOSFET is deemed fully enhanced and RDS(ON)

voltage range from ground to VCC + 0.2V. This allows , LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology

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

the circuit breaker to operate as the load supply turns on from 0V.

Q1 SI4864DY

VIN VOUT Flexible Overcurrent Setting 1.25V 1.25V

+CIN 3.5A

CLOAD

The LTC4213 has an ISEL pin to select one of these three overcurrent settings:

GATE SENSENSENSEPVBIAS

3.3V VCC

ISEL at GND, VCB = 25m V and VCB(FAST) = 100m V 0.1µF

LTC4213 R4

ISEL left open, VCB = 50m V and VCB(FAST) = 175m V OFF ON ON READY

ISELGND

DN402 F01

ISEL at VCC, VCB = 100m V and VCB(FAST) = 325m V

Figure 1. The LTC4213 in an Electronic Circuit Breaker Application