Rainbow Electronics ATA6662 - Manual (Page 3)

3
4916E–AUTO–02/07
ATA6662 [Preliminary]
3. Functional Description
3.1 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 pre-normal mode
and INHIBIT is switched on. The supply current in sleep mode is typically 10 µA.
3.2 Ground Pin (GND)
The ATA6662 is neutral on the LIN pin in the case of a GND disconnection. It is able to handle a
ground shift up to 11.5% of V
S
.
3.3 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 2.0. 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 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; that is, during current limitation,
as the chip temperature increases, the current is reduced.
3.4 Input Pin (TXD)
This pin is the microcontroller interface to control the state of the LIN output. TXD is low to bring
LIN low. If TXD is high, the LIN output transistor is turned off. Then, the bus is in recessive mode
via the internal pull-up resistor. The TXD pin is compatible to both a 3.3V or 5V supply.
3.5 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 low longer than t
dom
> 6 ms, the pin
LIN will be switched off (recessive mode). To reset this mode, switch TXD to high (>10 µs)
before switching LIN to dominant again.
3.6 Output Pin (RXD)
This pin reports to the microcontroller the state of the LIN bus. LIN high (recessive) is reported
by a high level at RXD, LIN low (dominant) is reported by a low voltage at RXD. The output is an
open drain, therefore, it is compatible to a 3.3V or 5V power supply. The AC characteristics are
defined with a pull-up resistor of 5 k
Ω
to 5V and a load capacitor of 20 pF. The output is
short-current protected. In unpowered mode (V
S
= 0V), RXD is switched off. For ESD protection
a Zener diode is integrated, with V
Z
= 6.1V.