U6268B

Rev. A3, 11-Apr-01

1 (13)

Side-Airbag Sensor Dual Interface

Description

The U6268B is an interface IC for remote automotive
sensors. It links the crash sensors in the driver- and
passenger door with the main airbag unit in the
dashboard. Two identical channels supply the external
sensors and receive digital information from them via one
active wire each. The interface supplies the external
sensors with a pre-regulated smoothed voltage, the
external units transmit the digital information back to the

interface by current modulation.

As the device is for safety critical applications, highest
data transmission security is mandatory. With high
immunity against cross-coupling between the two
channels, the U6268B is tailored for the harsh automotive
environment.

Features

D Two identical interface channels
D Provides a pre-regulated smoothed voltage and a

supply current up to 50 mA for the sensors

D Receives data from the sensors by current modulation

with a transmission rate of 60 kBaud (transmission
bandwidth 500 kHz)

D Current modulation provides high noise immunity for

data transfer

D TTL-compatible input activate the sensor
D Data output can be directly connected to a micro-

controller input

D Operation supply voltage range 5.7 V v V

v 40 V

D ESD protection according to MIL-STD-883C test

method 3015.7

D High-level EMI protection

Benefits

D Voltage supply and data transmission with one active

wire over long distances

Block Diagram

Short circuit

detection

Temperature

monitor

Smoothed voltage

regulator

I/V converter

Smoothed voltage

regulator

I/V converter

Voltage

comparator

Channel 1

Data

Enable

Voltage

comparator

Channel 2

Data

Crash

sensor

Channel 1

Channel 2

Channel 1

power
supply

Data

trans
mission

Crash

sensor

Channel 2

power
supply

Data

trans

mission

13839

Figure 1. Block diagram

Ordering Information

Extended Type Number

Package

Remarks

U6268BFP

SO16

U6268B

Rev. A3, 11-Apr-01

2 (13)

Pin Description

OUT1

OUT2

RETURN2

GND

RETURN1

13321

CLL1

OCM1

OCM2

CLL2

ENABLE2

GND

ENABLE1

Figure 2. Pinning

Symbol

Function

GND

Ground and reference pin

RETURN1

Return line of the external unit,
internally connected to GND via
a line-protection transistor

OUT1

Voltage-stabilized supply output
and current-modulation input

Supply voltage of the IC

OUT2

Voltage stabilized supply output
and current modulation input

Smooth time constant for slow
voltage change at both OUT
pins

RETURN2

Return line of the external unit,
internally connected to GND via
a line-protection transistor

8, 9

GND

Ground and reference pin

ENABLE2

Controls OUT1 voltage,
ENABLE1 High means OUT1
active, ENABLE1 Low or open
means OUT1 switched off

CLL2

Current logic level output, low
at high OUT2 current,
monitoring via OCM2

OCM2

Analog current output, repre-
senting 1/10 current of OUT2

OCM1

Analog current output, repre-
senting 1/10 current of OUT1

CLL1

Current logic level output, low
at high OUT1 current, moni-
toring via OCM1

ENABLE1

Controls OUT2 voltage,
ENABLE2 High means OUT2
active, ENABLE1 Low or open
means OUT2 switched off

GND

Ground and reference pin

U6268B

Rev. A3, 11-Apr-01

4 (13)

Functional Description

The IC and the external units are powered via the V

Pin 4. This pin is connected to the battery via a reverse
battery protection diode. An electrolythic capacitor of
22

mF smoothes the voltage and absorbes positive and

negative transients.

OUT1, OUT2

OUTx provides a smoothed, very slowly changing supply

voltage for the external units and monitors the output cur-
rent. During normal operating conditions, the OUTx
voltage is typ. 3 V below V

, and changes very slowly

with a varying battery voltage in order to suppress distur-
bances in the data transmission. At low V

(5.7 to 8.5 V),

the OUTx voltage is typ. 0.5 V below V

. This voltage

difference is reduced in order to ensure sufficient supply
voltage for the external unit between OUTx and
RETURNx. The output current capability is 50 mA. The
internal pull-down current at OUTx is typically 3 mA.

( V )

13322

out

22.4

21.4

9.4

8.2

5.4

4.9

7.7

5.7

8.5

11.3 12.0

28.6

32.6

Vout max

Vout min

(

)

Figure 4. Output voltage with tolerances vs. supply voltage

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 CLL-pin. The external
unit can switch on an additional current of 30 mA,
interpreted by the interface as logic low. The current
changes within approximately 1

ms, sufficient for a

transmission rate of about 60 kBaud, requiring a
transmission bandwidth of about 500 kHz for the current-
monitoring subcircuit and the OCM output. For a good
current transmission behaviour, the dynamic resistance of

OUTx may not exceed 12

W inside the bandwidth range

(total of 15

W 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 overtemperature- and short-circuit
protected. A reverse polarity diode at Pin V

(Pin 4) en-

sures that no current is fed back to the V

Batt

-system in the

case of a short between OUTx and V

Batt

. A minimum ca-

pacity of 33 nF is required at the pins OUTx.

U6268B

Rev. A3, 11-Apr-01

5 (13)

ENABLE1, ENABLE2

ENABLEx is a microcontroller-compatible input which
switches the related output on or off.

D Low or open circuit applied to ENABLEx switches off

the related OUTx and RETURNx (high impedance).
A sink current at Pin OUTx discharges the capacitive
load.

D High applied to ENABLEx switches on the related

OUTx and RETURNx to supply the external unit.

OCM1, OCM2

The output current of OUTx is monitored with a transmis-
sion factor of 0.1 to the OCMx. With a resistor from OCM
to GND, the current is converted to a voltage. The electri-
cal characteristics are specified by R

OCM

= 750

W. The

CLL-current threshold, the OUT-current limitation and
the OUT-current detection can be changed by varying
R

OCM

in a range from 500

W to 1 kW.

The current monitoring enables to detect overcurrent
conditions at OUTx (short circuit to GND or RETURNx)
and to detect low current conditions at OUTx (short cir-
cuit to V

Batt

or open load).

The internal pull-down current at the OUTx creates no
OCMx-current. During enable, the minimum voltage at
OCMx is the saturation voltage of an internal NPN-tran-
sistor with typically 0.1 V. The maximum voltage at
OCM is limited by an internal clamping diode to 5.3 V.

CLL1, CLL2

The current at Pin OUTx is evaluated logically and ready
to use for a microcontroller input. With this stage, the
logic data transmission from the external unit to the inter-
face is completed.

CLLx is the output stage of a comparator with an internal
threshold and with the OCMx input. A OCMx-voltage
higher than 2.4 V creates a logic low at CLLx, and a
OCMx-voltage lower than 1.43 V creates a logic high at
CLLx. The comparator has an internal hysteresis with
typically 0.4 V.

With the pull-down resistor R

OCMx

= 750

W at OCMx, the

correct OUTx-current threshold related to the logical out-
put CLLx is ensured. The CLLx is 'low' if the
OUTx-current is higher than 27.3 mA, and the CLLx is
'high', if the OUTx-current is lower than 19.1 mA. The
comparator has an internal hysteresis of typically 5 mA.
The tolerance of the R

OCM

resistor is assumed to be 0%.

The CLL-pin is an open-collector output and needs a
pull-up resistor of typically 2 k

W to the 5-V supply. For

ESD protection, a 7-V Zener diode is implemented.

RETURN 1, RETURN 2

The RETURNx pin provides a low-ohmic connection to
GND via a switched open-collector NPN-transistor. If
ENABLEx is high, RETURNx is switched on with a satu-
ration voltage less than 0.5 V at I

RETURNx

v 50 mA. If

ENABLEx is low or open, RETURNx is a current sink
with

v 2 mA. RETURNx is current-limited at typically

150 mA.

The smooth capacitor is designed to realize the long-time
constant for the slow voltage change at OUTx for both in-
terface channels. The capacity is typ. 22 nF. At the rising
edge of V

Batt

, the maximum slew rate is V

OUTx

= 5 V/ms,

and at the falling edge of V

Batt

, the maximum slew rate

is V

OUTx

= 10 V/ms.

GND-Pins

By means of a GND bond from the chip to Pin 1 and Pin 8,
high ground breakage security is achieved and lowest
voltage drop and ground shift between IC- and circuit
ground is provided. The four GND pins and the die pad
are directly connected to the copper leadframe, resulting
in a very low thermal resistance, R

thJC

. In order to achieve

a good thermal resistance, R

thJA,

a good copper connec-

tion from the four GND pins to the metal parts of the
modul housing is also recommended.

Power Dissipation

Worst case calculation of the supply current I

= 1,278

( I

OUT1

+ I

OUT2

) + 18 mA

Worst case calculation of the IC's power dissipation P

= (V

) [(V

diff

ret-sat

)

OUT1

+ I

OUT2

)

OCM

((I

OUT1

+ I

OUT2

) / 81)]

= 5.7 to 25 V supply voltage

diff

= V

to V

OUTx

voltage difference

diff

= 3.6 V at 12 V

v 25 V

diff

= 0.8 V at 5.7 V

v 8.5 V

ret-sat

= 0.5 V saturation voltage return

OUTx

= output current at Pin OUTx = 0 to 60 mA

OCM

= resistor at Pin OCMx

An overtemperature protection is integrated which gene-
rates a switch-off signal at a chip temperature of typically
T

= 160

C and a switch-on signal at typically T

= 150

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: U6268BFP

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: U6268BFP