6

LTC1477/LTC1478

ing of the switch parameters to the expected load current

and system current limit requirements.

A couple of examples are helpful:

1. If a nominal load of 1A was controlled by the switch

drop across the switch would be 70mV. The power

dissipated by the switch would only be 70mW.

2. If a nominal load of 0.5A was controlled by the switch

But the voltage drop would remain at 70mV and the

switch power dissipation would drop to 35mW.

Supply Bypassing

For best results, bypass the supply input pins with a single

1.0

µF capacitor as close as possible to the LTC1477.

Sometimes, much larger capacitors are already available

at the output of the power supply. In this case, it is still

good practice to use a 0.1

µF capacitor as close as possible

to the LTC1477, especially if the power supply output

capacitor is more than 2 inches away on the printed circuit

board.

Output Capacitor

The output pin is designed to ramp on slowly, typically

1ms rise time. Therefore, very large output capacitors can

be driven without producing voltage spikes on the supply

pins (see graphs in Typical Performance Characteristics).

The output pin should have a 1

µF capacitor for noise

reduction and smoothing.

Supply and Input Sequencing

The LTC1477 is designed to operate with continuous

power (quiescent current drops to < 1

µA when disabled).

If the power must be turned off, for example to enter a

system “sleep” mode, the enable input must be turned off

100

µs before the input supply is turned off to ensure that

the gate of the NMOS switch is completely discharged

before power is removed. However, the input control and

power can be applied simultaneously during power up.

0.85A Protected Switch

2A Protected Switch Driving a Large Capacitive Load

+

100

µF

0.1

µF

LTC1477/1478 • TA06

ON/OFF

2.7V TO 5.5V

LTC1477

GND

EN

+

1

µF

0.1

µF

LTC1477/1478 • TA05

ON/OFF

2.7V TO 5.5V

NC

NC

LTC1477

GND

EN

+

1

µF

0.1

µF

LTC1477/1478 • TA04

ON/OFF

2.7V TO 5.5V

NC

LTC1477

GND

EN

2A Protected Switch

1.5A Protected Switch

+

1

µF

0.1

µF

LTC1477/1478 • TA03

ON/OFF

2.7V TO 5.5V

GND

EN

LTC1477