STMicroelectronics Double output SMPS for power line application using ALTAIR04-900 primary controller EVLALTAIR900-M1 EVLALTAIR900-M1 Data Sheet

Doc ID 18211 Rev 2

17/29

The current control structure uses the voltage V

C

 to define the output current, according to 

(2). Actually, the CC comparator is affected by an internal propagation delay Td, which 
switches off the MOSFET with a peak current than higher the foreseen value.

This current overshoot is equal to:

where Lp is the primary inductance and it introduces an error on the calculated CC setpoint, 
depending on the input voltage.

The device implements a line feedforward function, which solves the issue by introducing an 
input voltage dependent offset on the current sense signal, in order to adjust the cycle-by-
cycle current limitation.

The internal schematic is shown in 

t

t

t

t

I

P

I

s

Q

I

C

T

R

V

I

C

CREF

−

=

CREF

I

         

         

(3)

IN

d

P

P

V T

ΔI

L

⋅

=