SP7661ERLSLASHTR datasheet(8/20 Pages) SIPEX

8 / 20 page

Mar -07 Rev N

SP766 Wide Input Voltage Range 3A, 600kHz Buck Regulator

SolvingforR9weget:

R9=[60mV•(R3+R4)]

[(IMAx •DCR)–60mV]

Asanexample:ifdesiredIMAxis17A,then

R9=63.4KΩ.

63.4KΩ

CSP

6.8nF

SWN

ISP

ISN

SP7661

0.1uF

5.11KΩ

L=2.7uH,DCR=4.1mΩ

VOUT

Over-current detection circuit for

Imax > 60mV / DCR

Decreasing the Current Limit

IfitisrequiredtosetIMAx<{60mV/DCR, a

resistorisaddedasshowninthefollowing

figure.R8increasesthenetvoltagedetected

bythecurrent-sensecomparator.Voltageat

thepositiveandnegativeterminalofcom-

paratorisgivenby:

VSP = VOut+(IMAx •DCR)

VSN = VOut •

{R8/(R4+R8)}

Sincethecomparatoristriggeredat60mV:

VSP-VSN=60mV

Combiningtheaboveequationsandsolv-

ingforR8:

R8=

R4 •

[VOut-60mV+(IMAX• DCR)]

60mV-(IMAX •DCR)

Asanexample:forIMAxof4AandVOutof3.3V,

calculatedR8is381kΩ.

CSP

6.8nF

ISN

SP7661

SWN

ISP

0.1uF

5.11KΩ

VOUT

L=2.7uH,DCR=4.1mΩ

1.5MΩ

Over-current detection circuit for

Imax < {60mV / DCR}

Handling of Faults

Uponthedetectionofpower(UVLO),ther-

mal,orshort-circuitfaults,theSP7661is

forcedintoanidlestatewheretheSSand

COMPpinsarepulledlowandbothswitches

areheldoff.IntheeventofUVLOfault,the

SP7661remainsinthisidlestateuntilthe

UVLOfaultisremoved.Uponthedetection

ofathermalorshort-circuitfault,aninternal

100mstimerisactivated.Intheeventofa

short-circuitfault,arestartisattemptedim-

mediatelyafterthe100mstimeoutexpires.

Whereas,whenathermalfaultisdetected

the100msdelaycontinuouslyrecyclesanda

restartcannotbeattempteduntilthethermal

faultisremovedandthetimerexpires.

THEORY OF OPERATION

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