ADP2147

Rev. 0 | Page 12 of 16

SIMPLE DYNAMIC VOLTAGE SCALING (DVS)

The ADP2147 has a VSEL pin that allows the user to force the

output voltage to change from one level (the default VOUT

setting) when VSEL is low and to another level (the alternate

VOUT setting) when VSEL is high. Transition between VOUT

levels is achieved within 40 μs when VOUT is commanded to go

from a lower voltage to a higher voltage. When VOUT is com-

manded to go from a higher VOUT voltage to a lower one, the

transition time depends on the load current present at that time.

SHORT-CIRCUIT PROTECTION

The ADP2147 includes frequency foldback to prevent output

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

feedback pin falls below half the target output voltage, indi-

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

frequency is reduced to half the internal oscillator frequency.

The reduction in the switching frequency allows more time for

the inductor to discharge, preventing a runaway of output current.

UNDERVOLTAGE LOCKOUT

To protect against battery discharge, undervoltage lockout

(UVLO) circuitry is integrated on the ADP2147. If the input

voltage drops below the 2.15 V UVLO threshold, the ADP2147

shuts down, and both the power switch and the synchronous

rectifier turn off. When the voltage rises above the UVLO

threshold, the soft start period is initiated, and the part is

enabled.

THERMAL PROTECTION

In the event that the ADP2147 junction temperature rises above

150°C, the thermal shutdown circuit turns off the regulator.

Extreme junction temperatures can be the result of high current

operation, poor circuit board design, or high ambient temperature.

A 20°C hysteresis is included so that when thermal shutdown

occurs, the ADP2147 does not return to operation until the on-

chip temperature drops below 130°C. When coming out of

thermal shutdown, a soft start is initiated.

SOFT START

The ADP2147 has an internal soft start function that ramps the

output voltage in a controlled manner upon startup, thereby

limiting the inrush current. The soft start minimizes input

voltage drop when a battery or a high impedance power source is

connected to the regulator’s input.

After the EN pin is driven high, internal circuits begin to power

up. Start-up time in the ADP2147 is the measure of when the

output is in regulation after the EN pin is driven high. Start-up

time consists of the power-up time plus the soft start time.

CURRENT LIMIT

The ADP2147 has protection circuitry to limit the amount of

positive current flowing through the PFET switch and the

synchronous rectifier. The positive current limit on the power

switch controls the amount of current that can flow from the

power source to the output. The negative current limit prevents

the inductor current from reversing direction and flowing out

of the load.

100% DUTY OPERATION

eventually reaches a limit where, even with the pFET switch on

At this limit, the ADP2147 smoothly transitions to a mode

where the PFET switch stays on 100% of the time. When the input

conditions change again and the required duty cycle falls, the

ADP2147 immediately restarts PWM regulation without