Datasheet

Example 1:
Setup12A tostartintoan80Wloadandcharge
a1600uFcapacitorinlessthan3ms.Setan
operationalI
LIMIT
of8.25 A +/ - 10%.
First,calculatehowmuchcurrentisneededfor
capacitorchargingandpoweringtheload;
I
STARTUP
=I
CHARGE
+ I
LOAD
=6.4A +6.67 A =13.7 A
Where;
I
CHARGE
=CV/T =1600uFx12V/.003s=6.4 A
I
LOAD
=P
LOAD
/V
LOAD
=80W/12V=6.67 A
NowcalculateR
SET
foranI
LIMIT
of13.7 A.
R
SET
= (I
LIMIT
xR
SENSE
xR
SUM
)/0.675
= 691 ! " (closest1%value=698 ! )
Where;
R
SUM
=6810 ! "
R
SENSE
=5m!
NowI
LIMIT
=0.675R
SET
/(R
SUM
R
SENSE
)=13.83 A
IfR0[3:0]aresetto0111and R6 [4]=1the
currentlimitwilldropto60%oftheprogrammed
maximumafterdroppingoutofcurrentlimit
followinginrush. Theoperationalcurrentlimitis
now;
I
LIMIT
=0.6xI
INRUSH
=0.6x13.83=8.3 A
The8.3 A limitcomplieswith8.25 A +/ - 10%.
Note - Thesecalculationsuseallnominalvalues
andneglectdi/dtratesatturnon.
TPS2359
SLUS792H –FEBRUARY 2008–REVISED MAY 2013 www.ti.com
Figure 25. Inrush Current Limiting Example 1
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