Datasheet

HVLED815PF Device description
Doc ID 023409 Rev 4 23/36
Figure 18. Voltage control principle: internal schematic
4.7 Voltage feed-forward block
The current control structure uses the V
CLED
voltage to define the output current, according
to equation
6 on Section 4.5 . Actually, the constant current comparator will be affected by an
internal propagation delay T
D
, which will switch off the MOSFET with a peak current than
higher the foreseen value.
This current overshoot will be equal to:
Equation 8
The previous terms introduce a small error on the calculated average output current set-
point, depending on the input voltage.
The HVLED815PF implements a line feed-forward 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
Figure 19 .
AM13568v1
Rdmg
Aux
Rfb
From CS pin
+
-
CV
To PWM Logic
R
C
COMP
DMG
S/H
DEMAG
LOGIC
+
-
EA
2.5V