Features
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Wide Power Supply Voltage Range
Short-circuit Protected K-interface, ISO9141 Compatible
Three Short-circuit Protected 40-mA Open-collector Buffers
All Low-power Outputs with Built-in 28-V Clamping
CMOS Compatible Digital Inputs with Hysteresis
Digital 1-mA Push-pull "RxD" K-line Output
Channel-specific Over-temperature Switch Off in Event of Short Circuit
Load-dump Protection and Interference Protection
According to ISO 7637-1/4 (DIN 40839)
Description
The U6812B is a bipolar monolithic K-line bus transceiver designed to provide
bi-directional serial communication in automotive diagnostic applications. The stan-
dard K-line is ISO 9141 compatible for baud rates up to 250 kBaud.
The IC provides three universally applicable 40-mA open-collector buffers, that can be
used for signal decoupling. The U6812B is manufactured using Atmel’s bipolar pro-
cess and fully complies to automotive industry specifications.The U6812B provides an
ideal grouping of SO-packaged low-power drivers, thus meeting customers’ demand
for space-saving and cost-effective circuit board assembly.
Single-ended
Bus Transceiver
with Triple
Buffer
U6812B
Figure 1.
Block Diagram
VS
VCC
VS
K-diagnosis ISO 9141
K
VS/2
TXD
VCC
TXD
VCC/2
GND
OUT 1
IN 1
VCC/2
VCC
GND
Temperature
control
IN 2
OUT 2
GND
DIS
OUT 3
IN 3
GND
Rev. 4760A–AUTO–10/03
Pin Configuration
Figure 2.
Pinning SO16
16
15
14
13
GND
K
TXD
RXD
GND
OUT 2
IN 2
DIS
VCC
IN 3
OUT 3
GND
1
2
3
4
U6812B
5
6
7
8
12
VS
11 IN 1
10 OUT 1
9
GND
Pin Description
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Symbol
GND
OUT 2
IN 2
DIS
VCC
IN 3
OUT 3
GND
GND
OUT 1
IN 1
VS
RXD
TXD
K
GND
Type
Supply
Open-collector output
Digital input
Digital input
Supply
Digital input
Open-collector output
Supply
Supply
Open-collector output
Digital input
Supply/reference
Digital output
Digital input
12-V input and O.C. output
Supply
Function
Ground; all ground pins are directly connected to the lead frame
Protected output of driver 2 (faced to: outside)
Input of protected driver 2 (faced to: µP)
Disable input for OUT 2 and OUT 3, “H”=enable, “L”=disable
+5-V supply
Input of protected driver 3 (faced to: µP)
Protected output of driver 3 (faced to: outside)
Ground
Ground
Protected output of driver 1 (faced to: outside)
Input of protected driver 1 (faced to: µP)
+12-V reference for K-line level
Diagnosis receive line (faced to: µP)
Diagnosis transmit line (faced to: µP)
Bi-directional diagnosis line (faced to: outside)
Ground
2
U6812B
4760A–AUTO–10/03
U6812B
Figure 3.
Basic Application Circuit
V
Batt
D
1
C
1
10 µ
+
R
1
1k
K
C
2
TXD
RXD
IN 1
OUT 1
V
S
16
15
14
13
12
11
10
9
U6812B
1
2
3
4
5
6
7
8
IN 2
OUT 3
DIS
OUT 2
VCC
IN 3
3
4760A–AUTO–10/03
Functional Description
K-interface
The K-interface is equipped with a 40-mA open-collector driver. The current is deter-
mined by the external pull-up resistor. The saturation voltage is below 0.6 V.
The open-collector output is protected by a 28-V Z-diode. The collector current is per-
manently monitored for short circuits via a built-in shunt. In the event of a short circuit
occurring at V
Batt
, the collector current is held at approximately I
creg
= 80 mA; the chip
temperature then rises due to power loss. This status is maintained until the detection of
overtemperature which causes the K-line output to be disabled and stored to memory.
The internal short-circuit detection threshold is I
sc
> 0.8
´
I
creg
. The output remains dis-
abled until a falling edge of a pulse is available to its input. Any further attempt to
connect while the short circuit is still present causes the above sequence to be
repeated. The output can be activated normally once the short circuit has been
removed. The maximum baud rate is 250 kBaud.
The K-line allows bi-directional communication with the microcontroller. When the out-
put K is disabled, information can be transferred to the processor via the input
comparator at pin RxD.
The digital output RxD is a push-pull output stage with a driver power of 1 mA.
In the event of a line break at the K-line, the output K is connected to GND via the built-
in 85-k
W
pull-down resistor, thus allowing the microcontroller to detect this fault. The
maximum sampling frequency is 250 kBaud.
Open-collector Driver
OUTx
The outputs are designed for a maximum static current of 40 mA, which is determined
by the external pull-up resistor. The saturation voltage is below 0.6 V
The three OUTx-driver outputs are activated with "active low" at the corresponding
input. Outputs OUT2 and OUT3 can also be disabled with "active low" at the disable
input, regardless of their input signal. The outputs are released by an open disable input
or by using high potential.
The open-collector outputs are connected to a 28-V Z-diode. The collector current is
permanently monitored via a built-in shunt circuit to permit the detection of short circuits.
If a short circuit occurs at V
Batt
, the collector current is held at approximately
I
creg
= 80 mA; accompanied with a rise of chip temperature due to power loss. This sta-
tus is maintained until the detection of overtemperature which causes the output
affected by the short circuit to be selectively disabled and stored to memory. The inter-
nal short-circuit detection threshold is I
sc
> 0.8
´
I
creg
. The affected output remains
disabled until a falling edge of a pulse is available to its input. Any further attempt to con-
nect while the short circuit is still present causes the above sequence to be repeated.
The output can be activated normally once the short circuit has been removed.
Power Supply
The IC must be equipped with external RC circuitry to limit the voltage in the event of
power surges (see Figure 3 on page 3). This prevents the circuit from being damaged or
destroyed, and provides a buffer in case of power fluctuations at V
Batt
. The RxD compar-
ator is powered via pin V
S
, producing its reference voltage of 1/2 V
S
, while all other
blocks are supplied via V
CC
.
The operating voltage can vary between V
S
= 7 V and 26 V. The resistor R
1
at pin V
S
lim-
its the current via the built-in 28-V Z-diode between V
S
and GND.
4
U6812B
4760A–AUTO–10/03
U6812B
Application Note
It is recommended to use the external components as shown in Figure 3 on page 3 with
the reverse battery protection diode D
1
and the buffer capacitor C
1
= 10 µF.
The digital inputs are CMOS-compatible and equipped with a built-in pull-up resistor
with a typical rating of 85 k
W
to V
CC
. The input threshold totals V
TH
= 0.57
´
V
CC
with a
typical hysteresis of 100 mV. The inputs are designed for an input voltage of -0.2 V to
V
CC
+ 0.6 V.
For proper activation of the output stages, it is mandatory that the inputs are kept low as
long as the supply voltage is not applied. When the supply voltage has been applied, all
inputs need to have a falling edge (see “Timing Diagrams” on page 6).
Digital Inputs (DIS, IN 1,
IN 2, IN 3 and TxD)
Digital Output (RxD)
The digital output RxD is a push-pull output stage with a driver power of I
RxD
= 1 mA.
Interference Voltages
The U6812B is protected against interference pulses (usually present in the wiring) by
and Load Dump (Defined
the recommended R
1
C
1
circuitry and the integrated elements (28-V Z-diodes, both at
in DIN40839 or ISO7637)
the supply pin and at the output pins and two diodes connected to V
CC
and GND at the
digital inputs). All transient pulses, which appear on the supply line (V
Batt
), should not
affect the function of the IC (see Table 1).
Table 1.
Transient Test Conditions
Name
DIN/ISO 1
DIN/ISO 2
DIN/ISO 3a
DIN/ISO 3b
DIN/ISO 5
Voltage
-110 V
110 V
-160 V
150 V
55 V (total)
Source Resistance
10
W
10
W
50
W
50
W
2
W
Rise Time
100 V/µs
100 V/µs
30 V/ns
20 V/ns
10 V/ms
Pulse Duration
2 ms
0.05 ms
0.1 µs
0.1 µs
500 ms
Pulse Amount
15000
15000
1 h (reference to ISO)
1 h (reference to ISO)
20
Table 2.
Truth Table
WSI-1
L
H
L
X
X
X
WSI-2
L
H
L
X
X
X
WSI-R
X
X
X
H
L
X
EN
H
X
L
X
X
X
TXD
X
X
X
H
L
X
K
X
X
X
Open
L
H
WSO-1
L
Open
Open
X
L
X
WSO-2
L
Open
Open
X
X
X
WSO-R
X
X
X
Open
L
X
RXD
X
X
X
H
L
H
5
4760A–AUTO–10/03
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