Data Sheet

ADP5301

Rev. A | Page 15 of 21

UNDERVOLTAGE LOCKOUT (UVLO)

The undervoltage lockout circuitry monitors the input voltage

level on the PVIN pin. If input voltage falls below 2.00 V (typical),

the regulator turns off. After the input voltage rises above 2.06 V

(typical), the soft start period is initiated, and the regulator is

enabled when the EN pin is high.

ENABLE/DISABLE

The ADP5301 includes a separate enable pin (EN). A logic high

in the EN pin starts the regulator. Due to the low quiescent current

design, it is typical for the regulator to start switching after a delay

of a few milliseconds from the EN pin being pulled high.

A logic low on the EN pin immediately disables the regulator

and brings the regulator into extremely low current consumption.

CURRENT LIMIT

The buck regulator in the ADP5301 has protection circuitry

that limits the direction and the amount of current to a certain

level that flows through the high-side MOSFET and the low-side

MOSFET in cycle-by-cycle mode. The positive current limit on

the high-side MOSFET limits the amount of current that can flow

from the input to the output. The negative current limit on the

low-side MOSFET prevents the inductor current from reversing

direction and flowing out of the load.

SHORT-CIRCUIT PROTECTION

The buck regulator in ADP5301 includes frequency foldback to

prevent current runaway on a hard short. When the output voltage

at the FB pin falls below 0.3 V typical, indicating the possibility

of a hard short at the output, the switching frequency (in PWM

mode) is reduced to one-fourth of the internal oscillator frequency.

The reduction in the switching frequency allows more time for the

inductor to discharge, preventing a runaway of output current.

SOFT START

The ADP5301 has an internal soft start function that ramps up

the output voltage in a controlled manner upon startup, thereby

limiting the inrush current. This feature prevents possible input

voltage drops when a battery or a high impedance power source

is connected to the input of the device. The default typical soft

start time is 350 µs for the regulator.

A different soft start time (2800 µs) can be programmed for

ADP5301 by the factory fuse.

STARTUP WITH A PRECHARGED OUTPUT

The buck regulator in the ADP5301 includes a precharged

start-up feature to protect the low-side MOSFET from damage

during startup. If the output voltage is precharged before the

regulator turns on, the regulator prevents reverse inductor

current—which discharges the output capacitor—until the

internal soft start reference voltage exceeds the precharged

voltage on the feedback pin.

100% DUTY CYCLE OPERATION

When the input voltage approaches the output voltage, the

ADP5301 stops switching and enters 100% duty cycle operation. It

connects the output via the inductor and the internal high-side

power switch to the input. When the input voltage is charged

again and the required duty cycle falls to 95% typical, the buck

immediately restarts switching and regulation without allowing

overshoot on the output voltage. In hysteresis mode, the ADP5301

draws an ultralow quiescent current of only 570 nA typical during

100% duty cycle operation

ACTIVE DISCHARGE

The ADP5301 integrates an optional, factory programmable

discharge switch from the switching node to ground. This switch

turns on when its associated regulator is disabled, which helps

discharge the output capacitor quickly. The typical value of the

discharge switch is 290 Ω for the regulator.

By default, the discharge function is not enabled. The active

discharge function can be enabled by the factory fuse.

VOUTOK FUNCTION

The ADP5301 includes an open-drain power-good output

(VOUTOK pin) that is active high when the buck regulator is

operating normally. By default, the VOUTOK pin monitors the

output voltage. A logic high on the VOUTOK pin indicates that

the regulated output voltage of the buck regulator is above 90%

(typical) of its nominal output. When the regulated output voltage

of the buck regulator falls below 87% (typical) of its nominal output

for a delay time greater than approximately 10 µs, the VOUTOK

pin goes low.

THERMAL SHUTDOWN

If the ADP5301 junction temperature exceeds 142°C, the thermal

shutdown circuit turns off the IC except for the internal linear

regulator. Extreme junction temperatures can be the result of

high current operation, poor circuit board design, or high ambient

temperature. A 15°C hysteresis is included so that the ADP5301

does not return to operation after thermal shutdown until the

junction temperature falls below 127°C. When the device exits

thermal shutdown, a soft start is initiated for the buck regulator.