11/33

L6919E

Figure 4. Current Reading Timing (Left) and Circuit (Right)

phase and, in particular, the current measured in the middle of the oscillator period

The current information reproduced internally is represented by the second term of the previous equation as

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:

Rg

50

µµµµA

Rg

LGATEX

ISENX

PGNDSX

Track & Hold

Total current

information

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

=







⋅

–

==