ADP5304

Data Sheet

Rev. 0 | Page 12 of 17

The ADP5304 VINOK threshold also determines the time

when the buck regulator starts and stops switching. When the

input voltage is below the threshold, the regulator stops switching

in hysteresis mode. After the input source charges the input

capacitor voltage above a hysteresis from the threshold, the

regulator resumes switching. The regulator operates the input

voltage in a hysteresis window around the threshold considered

as the maximum power point tracking (MPPT). The high

impedance input power source or small input power application

employs the ADP5304 to charge the large output capacitor via

trickle charging.

Different VINOK thresholds are factory programmable from

2.05 V to 5.15 V in 50 mV steps. To order a device with options

other than the default options, contact your local Analog

Devices, Inc., sales or distribution representative.

CURRENT LIMIT

The buck regulators in the ADP5304 have 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 regulators in the ADP5304 include frequency foldback to

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

at the feedback pin (FB) falls below 0.3 V typical, indicating the

possibility of a hard short at the output, the switching frequency

in active mode reduces to half 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 ADP5304 has an internal soft start function that ramps the

output voltage in a controlled limitation upon startup, thereby

limiting the inrush current. This prevents possible input voltage

drops when a battery or a high impedance power source is

connected to the input of the device. The typical soft start

time or the regulator is 350 μs.

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

ADP5304 via the factory fuse (see Table 11).

STARTUP WITH PRECHARGED OUTPUT

The buck regulators in the ADP5304 include a precharged

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

during startup. If the output voltage is precharged before the

regulator is turned 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 OPERATION

When the input voltage approaches the output voltage, the

ADP5304 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. The ADP5304 draws an ultralow

quiescent current of only 640 nA typical during 100% duty cycle

operation.

ACTIVE DISCHARGE

The regulator in the ADP5304 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

THERMAL SHUTDOWN

If the ADP5304 junction temperature exceeds 142C, the thermal

shutdown circuit turns the IC off, 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 ADP5304

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 each enabled channel.