LTC4213 datasheet(10/22 Pages) AD

10 / 22 page

LTC4213

Rev. A

For more information www.analog.com

OPERATION

Overview

The LTC4213 is an electronic circuit breaker (ECB) that senses

load current with the the RDS(ON) of the external MOSFET

instead of using an external sense resistor. This No RSENSE

methodislessprecisethanRSENSEmethodduetothevariation

of RDS(ON). 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 exter-

nal 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 RDS(ON) of the external MOSFET.

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 compar-

ators are SENSEP and SENSEN pins. The voltage across

the drain and source of the external MOSFET is sensed at

SENSEP and SENSEN.

ΔVSENSE = VSENSEP − VSENSEN

(1)

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 compar-

ators are common mode to ground.

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 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 opera-

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

threshold 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 com-

parators. Above 2.07V bias supply voltage, the LTC4213

starts if the ON pin conditions are met. Short, shallow

bus bias supply transient dips below 1.97V of less than

80µs are ignored.

APPLICATIONS INFORMATION

Figure 1. LTC4213 Electronic Circuit Breaker Application

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

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