ADP5052ACPZ-R7 datasheet(21/40 Pages) AD

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Data Sheet

ADP5052

Rev. 0 | Page 21 of 40

FREQUENCY FOLDBACK

The buck regulators in the ADP5052 include frequency fold-

back to prevent output current runaway when a hard short

occurs on the output. Frequency foldback is implemented

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 switching frequency 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 to decrease but also increases the ripple cur-

rent during peak current regulation. This results in a reduction

in average current and prevents output current runaway.

Pulse Skip Mode Under Maximum Duty 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 frequency foldback of one-half. If the duty cycle increases

further, the PWM modulator skips two of every three PWM pulses,

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 ADP5052 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 are turned 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.

Note that careful design and proper component selection are

required to ensure that the buck regulator recovers from hiccup

mode under heavy loads. Hiccup protection can be enabled or

disabled for all four buck regulators by factory fuse. When hiccup

protection is disabled, the frequency foldback feature is still avail-

able for overcurrent protection.

LATCH-OFF PROTECTION

The buck regulators in the ADP5052 have an optional latch-off

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

circuit and overvoltage conditions. Latch-off mode can be enabled

by 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 overcurrent status

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

attempts to restart. If seven continuous restart attempts are made

and the regulator remains in the fault condition, the regulator is

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

by reenabling the channel or by resetting the channel power

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

hiccup protection is disabled.

Figure 46 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 46. Short-Circuit Latch-Off Detection

Overvoltage Latch-Off Mode

Overvoltage latch-off mode is enabled 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 47 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 47. Overvoltage Latch-Off Detection

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