U6268B Datasheet, PDF (4/14 Pages) TEMIC Semiconductors – Side-Airbag Sensor Dual Interface

3. Functional Description
3.1 V_S
The IC and the external units are powered via the V_S pin 4. This pin is connected to the battery
via a reverse battery protection diode. An electrolythic capacitor of 22 µF smoothes the voltage
and absorbs positive and negative transients.
3.2 OUT1, OUT2
OUTx provides a smoothed, very slowly changing supply voltage for the external units and mon-
itors the output current. During normal operating conditions, the OUTx voltage is typically 3V
below V_S, and changes very slowly with a varying battery voltage in order to suppress distur-
bances in the data transmission. At low V_S (5.7V to 8.5V), the OUTx voltage is typically 0.5V
below V_S. This voltage difference is reduced in to ensure sufficient supply voltage for the exter-
nal unit between OUTx and RETURNx. The output current capability is 50 mA. The internal pull-
down current at OUTx is typically 3 mA.
Figure 3-1. Output Voltage with Tolerances versus Supply Voltage
35
30
25
22.4
21.4
20
15
9.4
8.2 _7.7
5.4
4.9
10
5
0
0
Voutmax
Voutmin
5
10
15
20
25
30
35
40
12.0
5.7 8.5 _11.3
V_S (V)
28.6 32.6
The data transmission from the external unit to the interface IC is carried out on the same line by
varying the current level. The quiescent current consumption of the external unit is about 5 to
15 mA. This current level is interpreted as logic high level at the CLL pin. The external unit can
switch on an additional current of 30 mA, interpreted by the interface as logic low. The slope
time of the current pulse is approximately 1 µs which is suitable for a transmission rate up to
60 kBaud. The necessary transmission bandwidth of greater than 500 kHz between OUTx and
OCMx is guaranteed (see “Application Circuit” on page 12). To achieve good current transmis-
sion behavior, the dynamic resistance of OUTx may not exceed 12Ω within the bandwidth range
(total of 15Ω for OUTx and RETURN).
The OUTx voltage can be switched off by ENABLEx = LOW to reset the external unit and to
reduce power dissipation during fault conditions.
The OUT pins are protected against overtemperature and short circuits. A reverse polarity diode
at pin V_S (pin 4) ensures that no current is fed back to the V_Batt system in the case of a short
between OUTx and V_Batt. A minimum capacity of 33 nF is required at the pins OUTx.
4 U6268B
4808B–AUTO–09/05