L6997

10/23

be supposed linear function of the time.

Eq 8

so the output voltage is given by:

Eq 9

Eq 10

Eq 11

1.5 Current limit

pares this value with the ILIM pin voltage value. While the current is above the current limit value, the control

inhibits the one-shot start.

To properly set the current limit threshold, it should be noted that this is a valley current limit. Average current

The average output current in current limit is given by:

Eq 12

Thus, to set the current threshold, choose RILIM according to the following equation:

Eq 13

In current limit the system keeps the current constant until the output voltage meets the undervolatge threshold.

The negative valley current limit, for the sink mode, is set automatically at the same value of the positive valley

current limit. The average negative current limit differs from the positive average current limit by the ripple cur-

rent; this difference is due to the valley control technique.

The system accuracy is function of the exactness of the resistance connected to ILIM pin and the low side MOS-

tem linearity.

Figure 6. Current limit schematic

I

()

R

K

C

I

SS

t

⋅⋅

⋅

()

V

SS

C

SS

⋅

∆

()

-------------------------------------------------------------------

=

V

()

Qt,C

SS

()

C

ou t

-------------------------

R

K

C

I

SS

t

2

⋅⋅

⋅

()

C

ou t

V

SS

C

SS

2

⋅⋅

∆

⋅

()

----------------------------------------------------------------------

==

I

()

V

ou t

C

out

V

SS

C

SS

2

⋅⋅

∆

⋅⋅

()

R

K

C

I

SS

⋅⋅

()

----------------------------------------------------------------------------

0.5

=

I

OUT

CL

I

max valley

I

∆

2

-----

+

=

max valley

R

IL im

Rd s

on

----------------- K

ILIM

⋅

=

Positive and negative current limit

R

ILIM

5µA

Current

Comparator

To

logic

PGN

D

PHASE

To inductor

LS