ISL8013A datasheet(14/17 Pages) INTERSIL

14 / 17 page

FN7526.0

November 25, 2009

During power-up, the open-drain power good output

holds low for about 1ms after VOUT reaches the

regulation voltage. The PG output also serves as a 1ms

delayed the Power Good signal when the pull-up resistor

R1 is installed.

UVLO

When the input voltage is below the undervoltage

lock-out (UVLO) threshold, the regulator is disabled.

Soft Start-Up

The soft-start-up reduces the inrush 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 pre-biased output

condition.

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.

Discharge Mode (Soft-Stop)

When a transition to shutdown mode occurs or the VIN

UVLO is 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 Shut-Down

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.

Applications Information

Output Inductor and Capacitor Selection

To consider steady state and transient operations,

ISL8013A typically uses a 1.5µH output inductor. The

higher or lower inductor value can be used to optimize

the total converter system performance. For example, for

higher output voltage 3.3V application, in order to

decrease the inductor current ripple and output voltage

ripple, the output inductor value can be increased. It is

recommended to set the ripple inductor current

approximately 30% of the maximum output current for

optimized performance. The inductor ripple current can

be expressed as shown in Equation 1:

The inductor’s saturation current rating needs to be at

least larger than the peak current. The ISL8013A

protects the typical peak current 4.8A. The saturation

current needs be over 5.5A for maximum output current

application.

ISL8013A uses internal compensation network and the

output capacitor value is dependent on the output

FIGURE 37. SKIP MODE OPERATION WAVEFORMS

CLOCK

VOUT

NOMINAL +1.5%

NOMINAL

PFM CURRENT LIMIT

LOAD CURRENTT

PWM

PFM

8 CYCLES

ΔI

---------

–

⎝⎠

⎜⎟

⎛⎞

⋅

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

(EQ. 1)

ISL8013A

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