LTC1154 datasheet(8/16 Pages) LINER

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LTC1154

been set to minimize RFI and EMI emissions in normal

operation. If a short-circuit or current overload condition

is encountered, the gate is discharged very quickly (typi-

cally a few microseconds) by a large N-channel transistor.

Status Output Driver

The status circuitry continuously monitors the fault detec-

tion 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

removing drive from the gate as soon as an over-current

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

over-current protection by 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 approxi-

mately 10

µs 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 (<1

µF) 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, sole-

noids 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 10

µsdelaywillensurethattheover-

current 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

APPLICATI

I FOR ATIO

LTC1154 OPERATIO

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

100

µF

IRFZ24

15V

RLOAD

Ω

12V

CLOAD ≤ 1µF

0.036

Ω

LTC1154 • F01

STATUS

GND

LTC1154

Figure 1. Protecting Resistive Loads

STATUS

GND

LTC1154

100

µF

IRFZ24

15V

12V, 1A

SOLENOID

12V

1N5400

0.036

Ω

LTC1154 • F02

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