Data Sheet

ADP2389/ADP2390

SOFT START

The SS pin programs the soft start time. Place a capacitor

between the SS pin and GND; an internal current charges this

capacitor to establish the soft start ramp. Calculate the soft start

time using the following equation:

SS

SS

SS

I

C

V

t

×

= 6

.

0

where:

If the output voltage is precharged before power-up, the ADP2389/

ADP2390 prevent the low-side MOSFET from turning on until

the soft start voltage exceeds the voltage on the FB pin.

FAST TRANSIENT RESPONSE

The ADP2389/ADP2390 use the FTW pin to set the fast transient

and GND to program the window. Calculate the window

threshold using the following equation:

1

kΩ

200

+

=

FTW

R

Threshold

Window

If the output voltage is greater than the setting window, the fast

transient response is enabled. The fast transient response

function is disabled if the FTW pin is open and the minimum

window is 1%.

To avoid false trigger of the fast transient, the window threshold

must be 2× greater than the output ripple.

POWER GOOD

The power-good (PGOOD) pin is an active high, open-drain

output that requires an external resistor to pull it up to a voltage. A

logic high on the PGOOD pin indicates that the voltage at the

FB pin (and thus the output voltage) is within ±10% of the desired

value, and there is a 16 cycle waiting period before PGOOD is

pulled high. A logic low indicates that the voltage at the FB pin

is out of ±10% of the desired value, and there is a 16-cycle

waiting period before PGOOD is pulled low.

PEAK CURRENT-LIMIT AND SHORT-CIRCUIT

PROTECTION

The ADP2389/ADP2390 have a cycle-by-cycle peak current-

limit protection circuit to prevent current runaway. A resistor

limit threshold according to the following equation:

0.5

)

(k

1000

(A)

+

Ω

=

ILIM

OCP

R

I

For protection against heavy loads, the ADP2389/ADP2390 use

a hiccup mode for overcurrent protection. When the inductor T

turns off and the low-side MOSFET turns on until the next

cycle. The overcurrent counter increments during this process.

If the overcurrent counter reaches four or the FB pin voltage falls

to 0.2 V after the soft start, the device enters hiccup mode. During

hiccup mode, the high-side MOSFET and the low-side both turn

off. The device remains in this mode for seven soft start times and

then attempts to restart from soft start. If the current-limit fault is

cleared, the device resumes normal operation; otherwise, it

reenters hiccup mode.

In some cases, the input voltage (PVIN) ramp rate is too slow,

or the output capacitor is too large for the output to reach

regulation during the soft start process, which causes the

regulator to enter hiccup mode. To avoid such cases, use a

resistor divider at the EN pin to program the input voltage

UVLO, or use a longer soft start time.

OVERVOLTAGE PROTECTION (OVP)

The ADP2389/ADP2390 include an OVP feature that protects

the regulator against an output short to a higher voltage supply

or against a strong load disconnect transient. If the feedback

voltage increases to 0.7 V, the internal high-side MOSFET and

low-side MOSFET turn off until the voltage at FB decreases to

0.63 V. At that time, the ADP2389/ADP2390 resumes normal

operation.

UNDERVOLTAGE LOCKOUT (UVLO)

The undervoltage lockout (UVLO) threshold is 4.2 V with a 0.5 V

hysteresis, which prevents power-on glitches from occurring.

When the VIN voltage rises above 4.2 V, the device enables and

the soft start period initiates. When the VIN voltage drops

below 3.7 V, the device turns off.

THERMAL SHUTDOWN

In the event that the ADP2389/ADP2390 junction temperatures

rises above 150°C, the internal thermal shutdown circuit turns

off the regulator for self protection. Extreme junction temperatures

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

thermal design, and/or high ambient temperature. A 25°C

hysteresis is included in the thermal shutdown circuit so that if an

overtemperature event occurs, the ADP2389/ADP2390 does

not return to normal operation until the on-chip temperature

drops below 125°C. Upon recovery, a soft start initiates before

normal operation.

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