´

SS

RAMP

t

= 1260

C

(

)

2

´

AVG

LSS

SS

LOAD

RAMP

SENSE

i

V

=

t

2 × C

× C

× 100 × R

(

)

´

-

LOAD

IN(MAX)

LSS

CC

REF_K(MIN)

SENSE

C

V

V

t

=

V

R

SS2

RAMP

t

= 0.35

C

´

SS2

FLT(MIN)

54

t

C

=

3.75

´

(

)

SS2

CC

FLT(MIN)

54

t

t

C

=

3.75

´

+

TPS2394

SLVSAA9 – AUGUST 2010

www.ti.com

Due to the three-phase nature of the load current at turn-on, the load voltage ramp has potentially three distinct

phases. This profile depends on the relative values of load capacitance, input DC potential, maximum current

limit and other factors. The first two phases are characterized by the two different slopes of the current ramp; the

third phase, if required to complete load charging, is the constant-current charging at IMAX. Considering the two

current ramp phases to be one period at an average di/dt simplifies calculation of the required timing capacitor.

(3)

Where:

During this current ramp period, the load voltage magnitude which is attained is estimated by Equation 4.

(4)

Where:

considering the typical output values.

If the result of Equation 4 is larger than the maximum input supply value, then the load can be expected to

charge completely during the inrush slewing portion of the insertion event. However, if this voltage is less than

(5)

Where:

(6)

Where:

either Equation 7 or Equation 8, as appropriate.

(7)

(8)

Where:

12

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