Rainbow Electronics ATA6664 - Manual (Page 3)

3
9146E–AUTO–03/11
Atmel ATA6663/ATA6664
3. Functional Description
3.1 Physical Layer Compatibility
Since the LIN physical layer is independent from higher LIN layers (e.g., the LIN protocol
layer), all nodes with a LIN physical layer according to LIN2.x can be used along with LIN
physical layer nodes, which are according to older versions (i.e., LIN1.0, LIN1.1, LIN1.2,
LIN1.3), without any restrictions.
3.2 Supply Pin (V
S
)
Undervoltage detection is implemented to disable transmission if V
S
falls to a value below 5V
in order to avoid false bus messages. After switching on V
S
, the IC switches to fail-safe mode
and INHIBIT is switched on. The supply current in sleep mode is typically 10µA.
3.3 Ground Pin (GND)
The Atmel ATA6663/ATA6664 does not affect the LIN Bus in the case of a GND disconnec-
tion. 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 by LIN2.x. The voltage range is from –27V to +40V. This
pin exhibits no reverse current from the LIN bus to V
S
, even in the case of a GND shift or V
Batt
disconnection. The LIN receiver thresholds are compatible to the LIN protocol specifica-
tion.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: During current limi-
tation, as the chip temperature increases, the current is reduced.
Note: The internal pull-up resistor is only active in normal and fail-safe mode.
3.5 Input/Output 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 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 to both a
3.3V or 5V supply. During fail-safe Mode, this pin is used as output and is signalling the wake-
up source (see
Section 3.14 “Wake-up Source Recognition” on page 8 ). It is current limited to
< 8mA.
3.6 TXD Dominant Time-out Function (only Atmel ATA6663)
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 pin LIN will be switched off (recessive mode). To reset this mode, TXD needs to be
switched to high (> 10µs) before switching LIN to dominant again.
Note: The ATA6664 does not provide this functionality.