7

FN9218.0

October 13, 2005

capacitor value above 4.7

µF is not recommended as LDO

performance improvement is minimal.

Soft-start circuitry integrated into each LDO limits the initial

ramp-up rate to about 30

µs/V to minimize current surge.

The ISL9007 provides short-circuit protection by limiting the

output current to about 500mA.

The LDO uses an independently trimmed 1V reference as its

input. An internal resistor divider drops the LDO output

voltage down to 1V. This is compared to the 1V reference for

regulation. The resistor division ratio is programmed in the

factory to one of the following output voltages: 3.3, 2.85V,

2.8V, and 2.5V.

Overheat Detection

The bandgap outputs a proportional-to-temperature current

that is indicative of the temperature of the silicon. This

current is compared with references to determine if the

device is in danger of damage due to overheating. When

the die temperature reaches about 145°C, the LDO

momentarily shuts down until the die cools sufficiently. In the

overheat condition, if the LDO sources more than 50mA it

will be shut off. Once the die temperature falls back below

about 110°C, the disabled LDO is re-enabled and soft-start

automatically takes place.

ISL9007