Rainbow Electronics ATA6670 - Manual (Page 4)

4
9204C–AUTO–09/11
Atmel ATA6670 [Preliminary]
3. Functional Description
The functions described in the following text apply to each LIN transceiver. Therefore, if pin
LIN is stated, this applies to each of the two receivers (LIN1 and LIN2), which work completely
independently. The only internal connection is between GND1 and GND2. The functions only
available at transceiver 2 are marked accordingly.
3.1 Physical Layer Compatibility
Since the LIN physical layer is independent of higher LIN layers (e.g., the LIN protocol layer),
all nodes with a LIN physical layer according to revision 2.x can be mixed with LIN physical
layer nodes, which are based on older versions (i.e., LIN 1.0, LIN 1.1, LIN 1.2, LIN 1.3) without
any restrictions.
3.2 Supply Pin (VS)
Undervoltage detection is implemented to disable transmission if VS falls to a value below 5V
in order to avoid false bus messages. After switching on VS, the corresponding transceiver
switches to fail-safe mode. The supply current for each transceiver in sleep mode is typically
10µA.
3.3 Ground Pin (GND)
The Atmel ATA6670 does not affect the LIN bus in case of GND disconnection. It is able to
handle a ground shift up to 11.5% of V
S
.
3.4 Bus Pin (LIN)
A low-side driver with internal current limitation and thermal shutdown and an internal pull-up
resistor are implemented as specified for LIN 2.x. The voltage range is from –27V to +40V.
This pin exhibits no reverse current from the LIN bus to V
S
, even in case of a GND shift or V
Batt
disconnection. The LIN receiver thresholds are compatible with the LIN protocol specification.
The fall time (from recessive to dominant) and the rise time (from dominant to recessive) are
slope-controlled. The output has a self-adapting short-circuit limitation; in other words, during
current limitation, the current decreases in proportion to an increase in chip temperature.
Note: The internal pull-up resistor is only active in normal and fail-safe mode.
3.5 Input/ Pin (TXD)
In normal mode the TXD pin is the microcontroller interface to control the state of the LIN out-
put. TXD must be at the low level in order to have a low LIN bus. If TXD is high, the LIN output
transistor is turned off and the bus is in recessive state. The TXD pin is compatible with both a
3.3V and 5V supply.
3.6 TXD Dominant Time-out Function
The TXD input has an internal pull-down resistor. An internal timer prevents the bus line from
being driven permanently in dominant state. If TXD is forced to low longer than t
DOM
> 40ms,
the LIN pin is switched off (recessive mode). To reset this mode, switch TXD to high (> 10µs)
before switching LIN to dominant again.