ADP5053ACPZ-R7 datasheet(21/37 Pages) AD

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ADP5053

Data Sheet

Rev. B | Page 20 of 36

FREQUENCY FOLDBACK

The buck regulators in the ADP5053include frequencyfoldback to

prevent output current runaway when a hard short occurs

on the output. Implement frequency foldback as follows:

•

If the voltage at the FBx pin falls below half the target

output voltage, the switching frequency is reduced by half.

•

If the voltage at the FBx pin falls again to below one-fourth

the target output voltage, the switchingfrequency is reduced

to half its current value, that is, to one-fourth of fSW.

The reduced switching frequency allows more time for the

inductor current todecrease but also increases the ripplecurrent

during peak current regulation. This results in a reduction in

average current and prevents output current runaway.

Pulse Skip Mode Under MaximumDuty Cycle

Under maximum duty cycle conditions, frequency foldback

maintains the output in regulation. If the maximum duty cycle

is reached, for example, when the input voltage decreases, the

PWM modulator skips every other PWM pulse, resulting in a

switching frequencyfoldback ofone-half.Ifthe dutycycle increases

further, the PWM modulator skips two ofeverythree PWMpulses,

resulting in a switching frequency foldback to one-third of the

switching frequency. Frequency foldback increases the effective

maximum duty cycle, thereby decreasing the dropout voltage

between the input and output voltages.

HICCUP PROTECTION

The buck regulators in the ADP5053 include a hiccup mode for

overcurrent protection (OCP). When the peak inductor current

reaches the current-limit threshold, the high-side MOSFET turns

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

When hiccup mode is active, the overcurrent fault counter is

incremented. If the overcurrent fault counter reaches 15 and

overflows (indicating a short-circuit condition), both the high-

side and low-side MOSFETs turn off. The buck regulator

remains in hiccup mode for a period equal to seven soft start

cycles and then attempts to restart from soft start. If the short-

circuit fault has cleared, the regulator resumes normal operation;

otherwise, it reenters hiccup mode after the soft start.

Hiccup protection is masked during the initial soft start cycle to

enable startup of the buck regulator under heavy load conditions.

For the buck regulator to recover from hiccup mode under

heavy loads, careful design and proper component selection is

required. To enable or disable hiccup protection for all four buck

regulators, use the factory fuse. When hiccup protection is

disabled, the frequency foldback feature continues to be available

for overcurrent protection.

LATCH-OFF PROTECTION

The buck regulators in the ADP5053 have an optional latch-off

mode to protect the device from serious problems such as short-

circuit and overvoltage conditions.Enable latch-offmodeby

factory fuse.

Short-Circuit Latch-Off Mode

Short-circuit latch-off mode is enabled by factory fuse (on or off

for all four buck regulators). When short-circuit latch-off mode

is enabled and the protection circuit detects an overcurrentstatus

after a soft start, the buck regulator enters hiccup mode and

attempts to restart. If after completingseven continuous restart

attempts, the regulator remains in the fault condition, then the

regulator is shut down. This shutdown (latch-off) condition is

cleared only by reenablingthe channel or byresettingthe channel

power supply. Note that short-circuit latch-off mode does not

work if hiccup protection is disabled.

Figure 41 shows the short-circuit latch-off detection function.

OUTPUT

VOLTAGE

TIME

LATCH-OFF

LATCH OFF

THIS

REGULATOR

SHORT CIRCUIT DETECTED

BY COUNTER OVERFLOW

PWRGD

7 ×

tSS

SCP LATCH-OFF

FUNCTION ENABLED AFTER

7 RESTART ATTEMPTS

ATTEMPT TO

RESTART

Figure 41. Short-Circuit Latch-Off Detection

Overvoltage Latch-Off Mode

Enable overvoltage latch-off mode by factory fuse (on or off for

all four buck regulators). The overvoltage latch-off threshold is

124% of the nominal output voltage level. When the output

voltage exceeds this threshold, the protection circuit detects the

overvoltage status and the regulator shuts down. This shutdown

(latch-off) condition is cleared only by reenabling the channel

or by resetting the channel power supply.

Figure 42 shows the overvoltage latch-off detection function.

OUTPUT

VOLTAGE

TIME

LATCH OFF

THIS

REGULATOR

LATCH-OFF

124%

NOMINAL OUTPUT

100%

NOMINAL OUTPUT

CHx ON

Figure 42. Overvoltage Latch-Off Detection

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