LTC1981/LTC1982
5
OPERATIO
U
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
(<1µA).
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.
BLOCK DIAGRA SM
W
LTC1981 Single High Side Switch Driver
LTC1982 Dual High Side Switch Driver
REGULATING
CHARGE PUMP
EN
+
–
+
–
GATE
GDR
V
CC
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
will be approximately 2.5 times V
CC
or 7.25V, whichever is
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
will be approximately 2.5 times V
CC
or 7.25V, whichever is
less.
V
CC
(Pin 6): Input Supply Voltage. Range from 1.8V to␣ 5.5V.
PIN FUNCTIONS
UUU
