LTC4441 datasheet(8/18 Pages) LINER

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LTC1154

1154fb

APPLICATIONS INFORMATION

Figure 1. Protecting Resistive Loads

manner. The charge and discharge rates have been set to

minimize RFI and EMI emissions in normal operation. If

a short-circuit or current overload condition is encoun-

tered, the gate is discharged very quickly (typically a few

microseconds) by a large N-channel transistor.

OPERATION

Status Output Driver

The status circuitry continuously monitors the fault de-

tection logic. This open-drain output is driven low when

the gate of the MOSFET is driven low by the protection

circuitry. The status circuitry is reset along with the input

latch when the input, or ENABLE input, is cycled.

MOSFET and Load Protection

The LTC1154 protects the power MOSFET switch by remov-

ing drive from the gate as soon as an overcurrent condition

is detected. Resistive and inductive loads can be protected

with no external time delay in series with the drain sense

pin. Lamp loads, however, require that the overcurrent

protection be delayed long enough to start the lamp but

short enough to ensure the safety of the MOSFET.

Resistive Loads

Loads that are primarily resistive should be protected with

as short a delay as possible to minimize the amount of time

that the MOSFET is subjected to an overload condition. The

drain sense circuitry has a built-in delay of approximately

10μs to eliminate false triggering by power supply or load

transient conditions. This delay is sufﬁcient to “mask”

short load current transients and the starting of a small

capacitor (<1μF) in parallel with the load. The drain sense

pin can therefore be connected directly to the drain current

sense resistor as shown in Figure 1.

Inductive Loads

Loads that are primarily inductive, such as relays, solenoids

and stepper motor windings should be protected with as

short a delay as possible to minimize the amount of time

that the MOSFET is subjected to an overload condition.

The built-in 10μs delay will ensure that the overcurrent

protection is not false-triggered by a supply or load

transient. No external delay components are required as

shown in Figure 2.

Large inductive loads (>0.1mH) may require diodes con-

nected directly across the inductor to safely divert the

stored energy to ground. Many inductive loads have these

diodes included. If not, a diode of the proper current rating

should be connected across the load, as shown in Figure

2, to safely divert the stored energy.

Figure 2. Protecting Inductive Loads

100μF

IRFZ24

15V

RLOAD

12Ω

12V

CLOAD ≤ 1μF

0.036Ω

LTC1154 • F01

STATUS

GND

LTC1154

STATUS

GND

LTC1154

100μF

IRFZ24

15V

12V, 1A

SOLENOID

12V

1N5400

0.036Ω

LTC1154 • F02

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