MPQ8632 HIGH EFFICIENCY 18V SYNCHRONOUS STEP-DOWN CONVERTER FAMILY FOR 4A TO 20A
soft-start capacitor and then automatically retries
When the FB voltage drops to 80% of the REF
voltage or exceeds 120% of the nominal REF
voltage, the PG pin is pulled low.
soft-start. If the over-current condition still holds
after soft-start ends, the device repeats this
operation cycle until the over-current conditions
disappear and then output rises back to
regulation level. OCP offers non-latch protection.
If the input supply fails to power the MPQ8632,
the PG pin is also pulled low even though this pin
is tied to an external DC source through a pull-up
resistor (typically 100kΩ).
Low-Side Negative Current Limit: If the sensed
LS-FET negative current exceeds the negative
current limit, the LS-FET turns off immediately
and stays OFF for the remainder of the OFF
period. In this situation, both MOSFETs are OFF
until the end of a fixed interval. The HS-FET body
diode conducts the inductor current for the fixed
time.
Over-Current Protection (OCP)
The MPQ8632 features three current limit levels
for over-current conditions: high-side peak
current limit, low-side valley current limit and low-
side negative current limit.
However, the OCP operation mechanism of
MPQ8632GL-10 is different from other parts in
this family.
Over -Voltage Protection (OVP)
The MPQ8632 monitors the output voltage using
the FB pin connected to the tap of a resistor
divider to detect over-voltage. MPQ8632 and
MPQ8632H provide non-latch and latch off OVP
mode as showed in Table 1.
For MPQ8632GLE-10:
High-Side Peak Current Limit: The part has a
cycle-by-cycle over-current limiting function. The
device monitors the inductor current during the
HS-FET ON state. When the sensed inductor
current hits the peak current limit, the output
over-current comparator goes high, the device
enters OCP mode immediately and turns off the
HS-FET and turns on the LS-FET.
Table 1—OVP Mode
OVP Mode
Non-Latch Mode
MPQ8632-4
Latch-Off Mode
MPQ8632-6
MPQ8632-8
Part #
MPQ8632H-10
MPQ8632-12
MPQ8632-15
MPQ8632-20
MPQ8632-10
Low-Side Valley Current Limit: The device also
monitors the inductor current during the LS-FET
ON state. When ILIM=1 and at the end of the
OFF time, the LS-FET sourcing current is
compared to the internal positive-valley–current
limit. If the valley current limit is less than the LS-
FET sourcing current, the HS-FET remains OFF
and the LS-FET remains ON for the next ON time.
When the LS-FET sourcing current drops below
the valley current limit, the HS-FET turns on
again.
For MPQ8632GLE-10:
If the FB voltage exceeds the nominal REF
voltage but remains lower than 120% of the REF
voltage (0.611V), both MOSFETs are off.
If the FB voltage exceeds 120% of the REF
voltage but remains below 130%, the LS-FET
turns on while the HS-FET remains off. The LS-
FET remains on until the FB voltage drops below
110% of the REF voltage or the low-side
negative current limit is hit.
For other parts except MPQ8632GLE-10:
These parts enter OCP mode if only the LS-FET
sourcing valley current exceeds the valley current
limit. Once the OCP is triggered, the LS-FET
keeps ON state until the LS-FET sourcing valley
current is less than the valley current limit. And
then the LS-FET turns off, the HS-FET turns on
for a fixed time determined by frequency-set
resistor RFREQ and input voltage.
If the FB voltage exceeds 130% of the REF
voltage, then the device is latched off. Need
cycle the input power supply or EN to restart.
During OCP, the device tries to recover from the
over-current fault with hiccup mode: the chip
disables the output power stage, discharges the
MPQ8632 Rev.1.24
8/28/2013
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