MPQ8632-8 datasheet(23/46 Pages) MPS

23 / 46 page

MPQ8632 HIGH EFFICIENCY 18V SYNCHRONOUS STEP-DOWN CONVERTER FAMILY FOR 4A TO 20A

MPQ8632 Rev.1.24

www.MonolithicPower.com

8/28/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

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 100

kΩ).

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 RFREQ 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

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

Latch-Off Mode

Part #

MPQ8632-4

MPQ8632-6

MPQ8632-8

MPQ8632H-10

MPQ8632-12

MPQ8632-15

MPQ8632-20

MPQ8632-10

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.

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.

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