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LTC4213

4213f

APPLICATIO S I FOR ATIO

Figure 1 shows an electronic circuit breaker (ECB) appli-

cation. An external auxiliary supply biases the VCC pin and

the internal circuitry. A VIN load supply powers the load via

an external MOSFET. The SENSEP and SENSEN pins

OPERATIO

Overview

The LTC4213 is an Electronic Circuit Breaker (ECB) that

senses load current with the the RDSON of the external

MOSFET instead of using an external sense resistor. This

no RSENSE method is less precise than RSENSE method due

to the variation of RDSON. However, the advantages are

less complex, lower cost and reduce voltage and power

loss in the switch path owing to the absence of a sense

resistor. Without the external sense resistor voltage drop,

the VOUT improvement can be quite significant especially

in the low voltage applications. The LTC4213 is designed

to operate over a bias supply range from 2.3V to 6V. When

bias supply voltage and the ON pin are sufficiently high, the

GATE pin starts charging after an internal debounce delay

of 60µs. During the GATE ramp-up, the circuit breaker is

not armed until the external MOSFET is fully turned on.

Once the circuit breaker is armed, the LTC4213 monitors

the load current through the RDSON oftheexternalMOSFET.

Circuit Breaker Function

The LTC4213 provides dual level and dual response time

circuit breaker functions for overcurrent protection.

The LTC4213 circuit breaker function block consists of

two comparators, SLOWCOMP and FASTCOMP. The

thresholds of SLOWCOMP and FASTCOMP are VCB and

VCB(FAST). The ISEL pin selects one of the three settings:

1. VCB = 25mV and VCB(FAST) = 100mV with ISEL at GND

2. VCB = 50mV and VCB(FAST) = 175mV with ISEL floating

3. VCB = 100mV and VCB(FAST) = 325mV with ISEL at VCC

ISEL can be stepped dynamically, such as to allow a higher

circuit breaker threshold at startup and a lower threshold

after supply current has settled. The inputs of the com-

parators are SENSEP and SENSEN pins. The voltage

across the drain and source of the external MOSFET is

sensed at SENSEP and SENSEN.

∆VV

SENSE

SENSEP

SENSEN

−

()

When ∆VSENSE exceeds the VCB threshold but is less than

VCB(FAST), the comparator SLOWCOMP trips the circuit

breaker after a 16µs delay. If ∆VSENSE is greater than

VCB(FAST), the comparator FASTCOMP trips the circuit

breaker in 1µs.

A severe short circuit condition can cause the load supply

to dip substantially. This does not pose a problem for the

LTC4213 as the input stages of the current limit compara-

tors are common mode to ground.

sense the load current at the drain and source of the

external MOSFET. In ECB applications, large input bypass

capacitors are usually recommended for good transient

performance.

Undervoltage Lockout

An internal undervoltage lockout (UVLO) circuit resets the

LTC4213 if the VCC supply is too low for normal operation.

The UVLO comparator (UVCOMP) has a low-to-high thresh-

old of 2.07V and 100mV of hysteresis. UVLO shares the

glitch filters for both low-to-high transition (startup) and

high-to-low transition (reset) with the ON pin compara-

tors. Above 2.07V bias supply voltage, the LTC4213 starts

if the ON pin conditions are met. Short, shallow bus bias

4213 F01

LTC4213

VCC

READY

0.1µF

CLOAD

100µF

10k

ISEL

GND

GATE

SI4864DY

VCC

VOUT

1.25V

3.5A

SENSEN

SENSEP

VBIAS

2.5V

VIN

1.25V

CIN

100µF

OFF ON

Figure 1. LTC4213 Electronic Circuit Breaker Application

LTC4213IDDB Datasheet(PDF) 10 Page - Linear Technology

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