8

LTC1153

LTC1153 OPERATIO

Controlled Gate Rise and Fall Times

When the input is switched ON and OFF, the gate is

charged by the internal charge pump and discharged in a

controlled 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 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 input and

the gate charge control logic. The open-drain output is

driven low when the input is turned ON and the breaker is

latched off. The status circuitry is reset along with the input

latch when the auto-reset circuitry retries the breaker or

the input is cycled low.

Figure 1. Protecting Resistive Loads

Figure 2. Protecting Inductive Loads

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

MOSFET and Load Protection

The LTC1153 protects the power MOSFET switch by

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

condition is detected and breaking the circuit to the load.

Resistive and inductive loads can be protected with no

external time delay in series with the drain sense pin. High

inrush current loads, however, require that the trip delay

time be set long enough to start the load 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 switch or the load is subjected to an

overload condition. The drain sense circuitry has a built-

in trip delay of approximately 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

µs trip delay will ensure that the

breaker is not false-tripped by a supply or load transient.

No external delay components are required as shown in

Figure 2.

S

APPLICATI

I FOR ATIO

IN

STATUS

GND

DS

G

SD

LTC1153

0.22

µF

+

100

µF

IRFZ24

15V

12

Ω

12V

0.036

Ω

LTC1153 • F01

IN

STATUS

GND

DS

G

SD

LTC1153

0.22

µF

+

100

µF

IRFZ24

15V

12V, 1A

SOLENOID

12V

1N5400

0.036

Ω

LTC1153 • F02