5

LTC1156

ATIO

OPER

A voltage regulator with low standby current provides

continuous bias for the TTL to CMOS converters. 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.

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 power MOSFET 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 LTC1156 is configured to sense the drain current of

the power MOSFET in high side applications. An internal

100mV reference is compared to the drop across a sense

resistor (typically 0.002

Ω to 0.1Ω) 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 by a large N-channel transistor. A

simple RC network can be added to delay the over-current

protection so that large in-rush current loads such as

lamps or capacitors can be started.

Supply and Ground Pins

The two supply pins (3 and 8) of the LTC1156 must be

connected together at all times and the two ground pins (1

and 6) must be connected together at all times. The two

supply pins should be connected to the “top” of the drain

current sense resistor/s to ensure accurate sensing.

For further applications information, see the LTC1155

Dual High Side Micropower MOSFET Driver data sheet.

S

APPLICATI

TYPICAL

4-Cell Extremely Low Voltage Drop Regulator and Three Load

Switches with Short-Circuit Protection and 20

µA Standby Current

DS2

DS3

DS4

IN1

IN2

IN3

IN4

G2

G3

G4

GND GND

LTC1156

+

+

CONTROL

LOGIC

DS1

G1

REG ON/OFF

FAULT

1N4148

0.1

µF

100k

100k

5.2V TO 6V

4-CELL NiCd

BATTERY PACK

47

µF

0.1

µF

**0.03

Ω

3.3A MAX

5V/2A

SWITCHED

2

× Si9956DY

200pF

1

3

4

5

6

7

8

10k

LT1431

*470

µF

5V

LOAD

5V

LOAD

5V

LOAD

1156 TA02

+

* CAPACITOR ESR LESS THAN 0.5

Ω

** RCS02 ULTRONIX (303) 242-0810

IRLR024