MPQ8632-10 Datasheet, PDF (23/46 Pages) Monolithic Power Systems – High Efficiency 18V Synchronous Step-down Converter Family for 4A to 20A

MPQ8632 HIGH EFFICIENCY 18V SYNCHRONOUS STEP-DOWN CONVERTER FAMILY FOR 4A TO 20A
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.
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).
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.
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.
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 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 R_FREQ and input voltage.
During OCP, the device tries to recover from the
over-current fault with hiccup mode: the chip
disables the output power stage, discharges the
soft-start capacitor and then automatically retries
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.
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 -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.
Table 1—OVP Mode
OVP Mode Non-Latch Mode
MPQ8632-4
MPQ8632-6
MPQ8632-8
Part #
MPQ8632H-10
MPQ8632-12
MPQ8632-15
MPQ8632-20
For MPQ8632GLE-10:
Latch-Off Mode
MPQ8632-10
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.
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.
MPQ8632 Rev.1.24
www.MonolithicPower.com
23
8/28/2013
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