ISL8013A

FN7526 Rev 2.00

Page 13 of 16

November 17, 2014

PG

During power-up, the open-drain power-good output holds low for

output also serves as a 1ms delayed the power-good signal when

UVLO

When the input voltage is below the undervoltage lockout (UVLO)

threshold, the regulator is disabled. To adjust the voltage level of

power on and UVLO, use a resistive divider across EN. The input

between 10kΩ and 100kΩ.

Soft Start-up

The soft start-up reduces the in-rush current during the start-up.

The soft-start block outputs a ramp reference to the input of the

error amplifier. This voltage ramp limits the inductor current as

well as the output voltage speed so that the output voltage rises

in a controlled fashion. When VFB is less than 0.2V at the

beginning of the soft-start, the switching frequency is reduced to

1/3 of the nominal value so that the output can start-up

smoothly at light load condition. During soft-start, the IC operates

in the SKIP mode to support prebiased output conditions.

Enable

The enable (EN) input allows the user to control the turning on or

off the regulator for purposes such as power-up sequencing.

When the regulator is enabled, there is typically a 600µs delay

for waking up the bandgap reference and then the soft-start-up

begins. It is recommended that the EN voltage should be kept

slew rate.

such that the voltage is 1.4V (minimum enable logic high

Then select C such that the equivalent time constant is at least

2x the rise time, T. This will delay the EN voltage enough so that

reaches 2.5V. Use Equation 2 to get C:

Discharge Mode (Soft-Stop)

set, the outputs discharge to GND through an internal 100Ω

switch.

Power MOSFETs

The power MOSFETs are optimized for best efficiency. The

ON-resistance for the P-MOSFET is typically 50mΩ and the

ON-resistance for the N-MOSFET is typically 50mΩ.

100% Duty Cycle

The ISL8013A features 100% duty cycle operation to maximize

the battery life. When the battery voltage drops to a level that the

ISL8013A can no longer maintain the regulation at the output,

the regulator completely turns on the P-MOSFET. The maximum

dropout voltage under the 100% duty-cycle operation is the

product of the load current and the ON-resistance of the

P-MOSFET.

Thermal Shutdown

The ISL8013A has built-in thermal protection. When the internal

temperature reaches +140°C, the regulator is completely shut

down. As the temperature drops to +115°C, the ISL8013A

resumes operation by stepping through the soft-start.

1V

EN

FIGURE 37. EXTERNAL RESISTOR DIVIDER

C

VIN

EN

<400mV

2.5V

T

t (TIME)

–





1.4V

---------------------------------------------

=

(EQ. 1)

C

2T





--------------------



(EQ. 2)