7

LTC1710

OPERATIO

until about 300

lockout threshold (typically 2V). The circuit includes some

hysteresis and delay to avoid nuisance resets. Once opera-

100

µs to trigger another POR sequence.

Input Threshold

Anticipating the trend of lower and lower supply voltages,

While some SMBus parts may violate this stringent SMBus

sponding higher input supply voltage, the LTC1710 meets

and maintains the constant SMBus input threshold speci-

fication throughout the entire supply voltage range of 2.7V

to 5.5V.

Thermal Shutdown

In the unlikely event that either power switch overheats, a

thermal shutdown circuit, which is placed closely to the

two switches, will activate and turn off the gate drives to

both switches. The thermal shutdown circuit has a thresh-

old of 120

°C with a 15°C hysteresis.

Figure 3. Low Dropout Regulator Switching a 3.3V/300mA Supply

Figure 4. The LTC1710 Switching Two Different Voltage Loads

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Charge Pump

To fully enhance the internal N-channel power switches,

an internal charge pump is used to boost the gate drive to

charge pump output voltage limit is to protect the internal

switches from excessive gate overdrive. A feedback net-

work is used to limit the charge pump output once it is 6V

too fast, an internal current source is placed between the

output of the charge pump and the gate of the power

switch to control the ramp rate.

Since the charge pumps are driving just the gates of the

internal switches, only a small amount of current is

required. Therefore, all the charge pump capacitors are

integrated onboard. The drain of switch 1 is internally

controlled through Pin 1. In other words, SMBus devices

using different power supply voltages can be simulta-

neously switched by the same LTC1710.

Power-On Reset and Undervoltage Lockout

The LTC1710 starts up with both gate drives low. An

internal power-on reset (POR) signal inhibits operation

The LTC1710, when used with the LT

switch a regulated 3.3V/300mA supply to a load (Figure 3).

Also, with the help of the LT1304-5, the LTC1710 can be

used to make a boost switching regulator with output

disconnect and a low standby current of 22

µA (Figure 5).

81

2

10

µF

10

µF

7

5

6

FROM SMBus

3

PROGRAMMABLE

4

1710 F04

SW0D

5V

3.3V

CLK

DATA

OUT0

LTC1710

OUT1

AD1

GND

3.3V

LOAD

5V

LOAD

8

7

1

10

µF

1

µF

2

5

6

8

5

1

2

FROM SMBus

3

PROGRAMMABLE

4

1710 F03

SW0D

5V

CLK

DATA

SWITCHED

3.3V

OUT1

LTC1710

SHDN

SENSE

LT1521-3.3

OUT0

AD1

GND

1.5

µF

3.3V