A8650 datasheet(16/31 Pages) ALLEGRO

16 / 31 page

Low Input Voltage, Adjustable Frequency

2 A Synchronous Buck Regulator with EN/SYNC and Power OK

A8650

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

TABLE 1. Summary of A8650 Fault Modes and Operation

Fault

Mode

VSS

VCOMP

High-Side MOSFET

and fSW

Low-Side

MOSFET

POK

State

Reset

Condition

Output hard

short to ground

(VOUT =

VFB = 0 V)

Hiccup after

VCOMP ≈ 1.25 V

and 7

overcurrent faults

Clamped to ≈1.25 V

for ILIM, then pulled

low during hiccup

Controlled by VCOMP.

fSW/3 if

0< VFB<200 mV

Active during

tOFF(MIN),

Off during hiccup

Pulled low

Auto,

if short removed

Output

overcurrent

(heavy load) and

VFB < HICDIS

Hiccup after

VCOMP ≈ 1.25 V

and 7

overcurrent faults

Clamped to ≈1.25 V

for ILIM, then pulled

low during hiccup

Controlled by VCOMP.

fSW / 3 if

0< VFB< 200 mV,

fSW / 3 to fSW if

200 mV<VFB<600mV

Active during

tOFF(MIN),

Off during hiccup

Pulled low

Auto, if the load

decreases

SW hard short to

ground

Not affected;

hiccup may

occur when the

short is removed

Clamped to ≈1.25 V

for ILIM, then pulled

low if hiccup occurs

Controlled by VCOMP .

turned off if

VSW ≈ 0 V and blanking

time expires,

fSW / 3 if 0<VFB<200mV

Active during

tOFF(MIN),

Off if hiccup occurs

when the short is

removed

Depends on

VOUT

Auto,

if short removed

SW soft short to

ground

Hiccup after

VCOMP ≈ 1.25 V

and 7

overcurrent faults

Clamped to ≈1.25 V

for ILIM, then pulled

low during hiccup

Controlled by VCOMP.

fSW/3 if

0<VFB< 200 mV,

fSW/3 to fSW if

200 mV < VFB < 600 mV

Active during

tOFF(MIN),

Off during hiccup

Depends on

VOUT

Auto,

if short removed

FB pin open (FB

pin floats high

due to negative

bias current)

Not affected

Transitions low via

loop response as

VFB floats high

Off.

fSW / 3 if

0< VFB< 200 mV,

fSW/3 to fSW if

200 mV < VFB< 600 mV

Off.

Disabled if

VCOMP < 200 mV

(to limit negative

SW current)

Pulled low

Auto, if FB pin

connected to VOUT

Output

overvoltage

(VFB > 115% ×

VREF)

Not affected

Transitions low

via loop response

because

VFB > VREF

Off.

fSW / 3 if

0< VFB< 200 mV,

fSW/3 to fSW if

200 mV < VFB< 600 mV

Off.

Disabled if

VCOMP < 200 mV

(to limit negative

SW current)

Pulled low

Auto, if VFB returns

to the allowed

operating range

Output

undervoltage

(VFB < 92% ×

VREF)

Not affected

Transitions high

via loop response

because

VFB < VREF

Controlled by VCOMP.

fSW/3 if

0<VFB< 200 mV,

fSW/3 to fSW if

200 mV < VFB < 600 mV

Active during

tOFF(MIN)

Pulled low

Auto, if VFB returns

to the allowed

operating range

VIN dropout

or EN/SYNC

glitches low for

> 32 PWM cycles

Pulled low and

latched until

VSS < VSS_RESET

Pulled low and

latched until

VSS > VSSOFFS

Off

Pulled low

Auto, if VIN

recovers or

if EN/SYNC

returns high

Thermal

shutdown (TSD)

Pulled low and

latched until

VSS < VSS_RESET

Pulled low and

latched until

VSS > VSSOFFS

Off

Pulled low

Auto, if the junction

cools down

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