Datasheet

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 f
SW
.
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 ×
t
SS
SCP LATCH-OFF
FUNCTION ENABLED AFTER
7 RESTART ATTEMPTS
ATTEMPT TO
RESTART
10900-045
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
10900-046
CHx ON
Figure 47. Overvoltage Latch-Off Detection