7

LTC1153

TEST CIRCUITS

TI I G DIAGRA

LTC1153 OPERATIO

The LTC1153 is an electronic circuit breaker with built-in

MOSFET gate charge pump, over-current detection and

auto-reset circuitry. The LTC1153 consists of the follow-

ing functional blocks:

TTL and CMOS Compatible Inputs

The LTC1153 input and shutdown input have been de-

signed to accommodate a wide range of logic families.

Both input thresholds are set at about 1.3V with approxi-

mately 100mV of hysteresis.

A low standby current voltage regulator provides continu-

ous bias for the TTL-to-CMOS converter. The TTL-to-

CMOS converter output enables the rest of the circuitry. In

this way the power consumption is kept to a minimum in

the standby mode.

Auto-Reset Timer

current whenever a fault is detected, i.e., the switch

latched off. When the timing capacitor ramps up to ap-

proximately 2.5V, the switch is turned back on and the

timing capacitor discharged. If the circuit breaker output

is still in an overload state, the breaker will latch off and this

cycle will continue until the fault condition is removed.

Internal Voltage Regulation

The output of the TTL-to-CMOS converter drives two

regulated supplies which power the low voltage CMOS

logic and analog blocks. The regulator outputs are isolated

from each other so that the noise generated by the charge

pump logic is not coupled into the 100mV reference or the

analog comparator.

Gate Charge Pump

Gate drive for the MOSFET switch is produced by an

adaptive charge pump circuit which generates a gate

voltage substantially higher than the power supply volt-

age. The charge pump capacitors are included on-chip and

therefore no external components are required to generate

the gate drive.

Drain Current Sense

The LTC1153 is configured to sense the current flowing

into the drain of an N-channel MOSFET switch. An internal

100mV reference is compared to the drop across a sense

resistor (typically 0.002

Ω to 0.10Ω) in series with the

drain lead. If the drop across this resistor exceeds the

internal 100mV threshold, the input latch is reset and the

gate is quickly discharged via a relatively large N-channel

transistor.

OVER-CURRENT

(AUTO-CURRENT)

NORMAL

OFF

NOR-

MAL

SHUT-

DOWN

OFF

*90ms

*200

µs

S1 CLOSED

S1 OPEN

*TIMES FOR COMPONENTS SHOWN IN TEST CIRCUIT

LTC1153 • TD01

INPUT

OUTPUT

STATUS

TIMING

CAP

SHUT-

DOWN

IN

STATUS

GND

DS

G

SD

LTC1153

SHUTDOWN

8

7

6

5

1

2

3

4

0.05

Ω

IRLZ24

OUTPUT

S1

1

Ω

10

Ω

0.01

µF

0.1

µF

Z5U

51k

STATUS

INPUT

5V

LTC1153 • TC01