L6574
PIN CONNECTION
(top view)
CPRE
RPRE
CF
RING
OPOUT
OPIN-
OPIN+
EN1
1
2
3
4
5
6
7
8
D97IN492
16
15
14
13
12
11
10
9
VBOOT
HVG
OUT
N.C.
V
S
LVG
GND
EN2
THERMAL DATA
Symbol
R
th j-amb
Parameter
Thermal Resistance Junction to ambient
Max.
DIP16
80
SO16N
120
Unit
°C/W
PIN DESCRIPTION
N°
1
Pin
CPRE
Function
Preheat Timing Capacitor. The capacitor C
PRE
sets the preheating and the frequency shift time,
according to the relations: t
PRE
= K
PRE
· C
PRE
and t
SH
= K
FS
· C
PRE
(typ. K
PRE
= 1.5s/µF, K
FS
=
0.15s/µF). This feature is obtained by charging CPRE with two different currents. During tPRE
this current is independent of the external components, so CPRE is charged up to 3.5V (preheat
timing comparator threshold). During t
SH
the current depends on R
PRE
value (i.e. on the differ-
ence between f
PRE
and f
IGN
). In this way t
SH
is always set at 0.1t
PRE
. In steady state the voltage
at pin 1 is 5V.
Maximum Oscillation Frequency Setting. The resistance connected between this pin and ground
sets the fPRE value, fixing the difference between f
PRE
and f
IGN
(f
PRE
> f
IGN
). At the end of the
Start-up procedure, the effect current drown from R
PRE
is over. The voltage at this pin is fixed at
V
REF
=2V.
Oscillator Frequency Setting. The capacitor C
F
, along with to R
PRE
and R
IGN
, sets f
PRE
and f
ING
.
In normal operation this pin shows a triangular wave.
Minimum Oscillation Frequency Setting. The resistance connected between this pin and ground
sets the f
IGN
value. The voltage at this pin is fixed at V
REF
=2V.
Out of the operational amplifier. To implement a feedback control loop this pin can be connected
to the RIGN pin by means an appropriate circuitry.
Inverting Input of the operational amplifier.
Non Inverting Input of the operational amplifier.
Enable 1. This pin (active high), forces the device in a latched shutdown state (like in the under
voltage conditions). There are two ways to resume normal operation:
– the first is to reduce the supply voltage below the undervoltage threshold and then
increase it again until the valid supply is recognised.
– the second is activating EN2 input.
The enable 1 is especially designed for strong fault (e.g. in case of lamp disconnection).
2
RPRE
3
4
5
6
7
8
CF
RIGN
OPout
OPin-
OPin+
EN1
2/10
STMICROELECTRONICS [ STMICROELECTRONICS ]
