LTC1981/LTC1982

5

OPERATIO

Charge Pump

To fully enhance the external N-channel switches, internal

charge pumps are used to boost the output gate drive to

approximately 2.5 times the supply voltage, or 7.25V,

whichever is less. A feedback network is used to regulate

the output gate drive. This keeps the supply current low in

addition to providing a maximum output voltage limit. The

reason for the maximum output voltage limit is to avoid

switch gate source breakdown due to excessive gate

overdrive.

The gate drive outputs (GATE 1, GATE 2, or GATE) are

controlled by the shutdown input pins (SHDN 1, SHDN 2

or SHDN). A logic high input on one of the shutdown input

pins enables the corresponding charge pump and drives

the related gate drive output pin high. A logic low input on

one of the shutdown input pins disables the correspond-

ing charge pump and drives the related gate drive output

pin low. If shutdown input on the LTC1981 is low or both

of the shutdown input pins on the LTC1982 are low, the

part will be placed into a low current shutdown mode

(<1

µA).

Gate Drive Ready (LTC1981 Only)

The gate drive ready pin (GDR) is used to indicate when the

gate drive output (GATE) is greater than 90% of its final

value. This can be useful in applications that require

knowledge of the state of the gate drive for initialization

purposes or as fault detection should something be load-

ing the gate drive down.

LTC1981 Single High Side Switch Driver

LTC1982 Dual High Side Switch Driver

REGULATING

CHARGE PUMP

EN

+

–

+

–

GATE

GDR

REF

SHDN

1981/82 BD01

15k

REGULATING

CHARGE

PUMP 1

EN

GATE 1

SHDN 1

REGULATING

CHARGE

PUMP 2

EN

GATE 2

SHDN 2

1981/82 BD02

30k

30k

GATE 2(Pin 4): Gate Drive Output to an External High Side

Switch. Fully enhanced by internal charge pump. Con-

trolled by the SHDN 2 input pin. Output voltage on this pin

less.

GATE 1 (Pin 5): Gate Drive Output to an External High Side

Switch. Fully enhanced by internal charge pump. Con-

trolled by the SHDN 1 input pin. Output voltage on this pin

less.