L6919C

12/32

follow:

Since the current is read in differential mode, also negative current information is kept; this allow the device to

check for dangerous returning current between the two phases assuring the complete equalization between the

The transconductance resistor Rg can be designed in order to have current information of 25

µA per phase at

of the total delivered maximum current, results:

Since the device senses the output current across the low-side mosfets (or across a sense resistors in series

with them) the device limits the bottom of the inductor current triangular waveform: an over current is detected

Introducing now the maximum ON time dependence with the delivered current (where T is the switching period

This linear dependence has a value at zero load of 0.80·T and at maximum current of 0.40·T typical and results

in two different behaviors of the device:

< 35

µA).

voltage, the output resulting voltage will start to drop after crossing. In this case, the device doesn't perform con-

stant current limitation but only limits the maximum ON time following the previous relationship. The output volt-

I

IN FO x

R

SENSE

I

PHASE

⋅

R

g

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

=

I

OCPx

35

µARg

⋅

R

SEN SE

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

=

Rg

I

OC P x

R

SE NSE

⋅

35

µA

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

=

T

ON,MAX

0.80

I

FB

5.73 k

⋅

() T

⋅

–

0.80

R

SENSE

Rg

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

I

OUT

5.73k

⋅⋅



 T

0.80 T I

FB

⋅

0

µA

=

0.40 T I

FB

⋅

70

µA

=







⋅

–

==

a) Maximum output Voltage

characteristic

Desired Output

characteristic and

UVP threshold

Resulting Output

characteristic