U6084B
charged with a constant current, I, until the upper switch- A selection of different values of C and C , provides a
2
4
ing threshold is reached. A second current source is then range of oscillator frequency, f, from 10 to 2000 Hz.
activated which taps a double current, 2 I, from the
charging current. The capacitor, C , is thus discharged by
2
Pins 7, 8, 10 and 15
the current, I, until the lower switching threshold is
reached. The second source is then switched off again and
the procedure starts once more.
Not connected.
Example for Oscillator Frequency Calculation
Pin 9, Status Short Circuit Latch
(
)
R3
VT100
VT
VS
VS
VBatt
IS
IS
1
1
(
)
R3
VBatt
VBatt
100
2
2
The status of the short-circuit latch can be monitored via
Pin 9 (open collector output).
(
)
R3
VTL
VS
IS
3
3
where
VT100
Pin 9
L
H
Function
Short-circuit detected
No short-circuit detected
High switching threshold (100% duty cycle)
High switching threshold ( 100% duty cycle)
Low switching threshold
VT
100
VTL
Pins 11 and 12, Short-Circuit Protection
and Current Sensing
,
and are fixed constant.
3
1
2
The above mentioned threshold voltages are calculated
for the following values given in the data sheet.
1. Short-Circuit Detection and Time Delay, t
d
V
Batt
= 12 V, I = 4 mA, R = 150
,
S
3
= 0.7, = 0.67 and = 0.28.
1
2
3
The lamp current is monitored by means of an external
shunt resistor. If the lamp current exceeds the threshold
(
)
VT100
VT
12 V 4 mA 150
11.4 V 0.67
11.4 V 0.28
0.7
8 V
for the short-circuit detection circuit (V
90 mV), the
T2
7.6 V
3.2 V
duty cycle is switched over to 100% and the capacitor C
100
5
is charged by a current source of 20 A (I – I ). The
ch
dis
VTL
external FET is switched off after the cut-off threshold
(V ) is reached. Renewed switching on the FET is pos-
T11
For a duty cycle of 100%, an oscillator frequency, f, is
as follows:
sible only after a power-on reset. The current source, I
dis,
ensures that the capacitor C is not charged by parasitic
5
Iosc
currents. The capacitor C is discharged by I to typ.
0.7 V.
5
dis
f
, where C2
and Iosc
22 nF
A
(
)
2
VT100 VTL
C2
40
Therefore:
f
Time delay, t , is as follows:
d
40
A
189 Hz
(
)
2
8 V 3.2 V
22 nF
(
) ( )
td
C5 VT11 0.7 V Ich Idis
For a duty cycle of less than 100%, the oscillator fre-
quency, f, is as follows:
With C = 330 nF and V
= 12 V, we have
Iosc
5
Batt
f
(
)
2
VT
VTL
C2
4
VBatt C4
100
( )
330 nF 9.8 V 0.7 V 20 A
td
whereas
C = 470 pF
4
40
A
2
7.6 V 3.2 V
22 nF
4
12 V 470 pF
150 ms.
185 Hz
TELEFUNKEN Semiconductors
3 (8)
Rev. A1, 14-Feb-97
TEMIC [ TEMIC SEMICONDUCTORS ]
