ADP2370ACPZ-5.0-R7 datasheet(22/32 Pages) AD

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ADP2370/ADP2371

Data Sheet

Rev. A | Page 22 of 32

FEATURES DESCRIPTIONS

PRECISION ENABLE

The enable circuit of the ADP2370/ADP2371 minimizes the

input current during shutdown and simultaneously provides

an accurate enable threshold. When the enable input voltage

is below 400 mV, the regulators are in shutdown mode and the

supply current is typically 1.2 μA. As the enable input voltage

rises above the standby enable threshold of 1.0 V, the internal

bias currents and voltages are activated, turning on the precision

enable circuitry. This allows the precision enable circuitry to

detect accurately when the EN pin voltage exceeds the precision

enable rising threshold of 1.2 V.

FORCED PWM OR PWM/PSM SELECTION

Connecting the SYNC pin to a voltage greater than 1.2 V forces

the device to operate permanently in the PWM mode. This means

that the ADP2370/ADP2371 continue to operate at a fixed fre-

quency even when the output current is less than the PWM/PSM

threshold. In PWM mode, the efficiency is lower compared to the

PSM mode during light loads. The low-side NMOS remains on

when the output current drops to less than zero thereby preventing

the device from entering discontinuous conduction (DCC) mode.

It is possible to switch from FPWM mode to the power-save

mode during operation by pulling the SYNC pin low. The

flexible configuration of the SYNC pin during operation of

the device allows for efficient power management.

Connecting the SYNC pin to a voltage less than 0.4 V allows

the part to operate in either PWM or PSM modes, depending on

the output current. Whenever the average output current goes

below the PWM/PSM threshold, the ADP2370/ADP2371 enter

PSM mode operation. During PSM mode the part operates with

reduced switching frequency and with a minimal quiescent cur-

rent to maintain high efficiency. The low-side NMOS turns off

when the output current reaches zero, causing the part to operate

in DCC mode.

QUICK OUTPUT DISCHARGE (QOD) FUNCTION

The ADP2371 includes an output discharge resistor that forces the

output voltage to zero when the buck is disabled. This ensures

that the output of the buck is always in a well-defined state, whether

or not it is enabled. The ADP2370 does not include this output

discharge function.

SHORT-CIRCUIT PROTECTION

The ADP2370/ADP2371 include frequency foldback to prevent

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

the feedback pin falls below 0.3 V, indicating the possibility of

a hard short at the output, the switching frequency is reduced

to 1/4 of the internal oscillator frequency. The reduction in the

switching frequency gives more time for the inductor to dis-

charge, preventing a runaway of output current.

UNDERVOLTAGE LOCKOUT

To protect against battery discharge, an undervoltage lockout

(UVLO) circuit is incorporated into the ADP2370/ADP2371.

When the input voltage drops below the UVLO threshold, the

ADP2370/ADP2371 shuts down, and both the power switch

and synchronous rectifier turn off. Once the input voltage rises

above the UVLO threshold, the soft start period is initiated and

the device is enabled.

THERMAL PROTECTION

In the event that the junction temperature on either the ADP2370

or ADP2371 rises above 150°C, the thermal shutdown protec-

tion circuit turns off the regulator. Extreme junction temperature

can be the result of high current operation, poor circuit board

design, and/or high ambient temperature. A 20°C hysteresis is

included in the protection circuit so that when a thermal shut-

down occurs, the device does not return to operation until the

on-chip temperature drops below 130°C. When exiting a

thermal shutdown, soft start is initiated.

SOFT START

The ADP2370/ADP2371 have an internal soft start function

that ramps the output voltage in a controlled manner upon

startup, thereby limiting the inrush current. This prevents

possible input voltage drops when a battery or a high imped-

ance power source is connected to the input of the converter.

Typical soft start time is 350 μs. The ADP2370/ADP2371 are

also capable of starting up into a precharged output capacitor.

If soft start is invoked when the output capacitor charge is greater

than zero, the device delays the start of switching until the internal

soft start ramp reaches the corresponding FB voltage. This fea-

ture prevents discharging the output capacitor at the beginning

of soft start.

CURRENT LIMIT

The ADP2370/ADP2371 have protection circuitry that limits

the direction and amount of current to 1200 mA that flows

through the power switch and synchronous rectifier, cycle by

cycle. The positive current limit on the power switch limits the

amount of current that can flow from the input to the output.

The negative current limit on the synchronous rectifier prevents

the inductor current from reversing direction and flowing out

of the load.

A negative current limit is provided by the ADP2370/ADP2371

to prevent an excessive reverse inductor current when the switching

section sinks current from the load in forced continuous con-

duction mode. Under negative current-limit conditions, both

the high-side and low-side switches are disabled.

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