3
ATA6663/ATA6664 [APPLICATION NOTE]
9201B–AUTO–06/15
1.
Hardware Description
In the following sections only the normal operating conditions are described. Refer to the corresponding datasheet for
detailed information about the features mentioned.
1.1
Power Supply (VBAT, +5V and GND)
The development board requires an external 5.7V to 27V DC power supply between the terminals VBAT and GND. The
input circuit is protected against inverse polarity with the protection diode D1, resulting in a difference between the VBAT and
VS level of approximately 0.7V.
The DC voltage at pin +5V is only required for activating the pull-up resistor for the pin RXD.
1.2
LIN Interface (LIN, TXD and RXD)
1.2.1
Bus Pin (LIN)
A low-side driver with internal current limitation, thermal shutdown, and an internal pull-up resistor in compliance with LIN
spec 2.x is implemented. The internal pull-up resistor is active in normal and fail-safe mode. The LIN receiver thresholds are
compatible with the LIN protocol specification. The reverse current from the LIN bus to Vs is <2µA, even when Vbat is
disconnected.
At a short circuit between LIN and V
Battery
, the output limits the output current. Due to the power dissipation, the chip
temperature exceeds the overtemperature threshold and the LIN output is switched off. The chip cools down and after the
temperature hysteresis the output switches on again. RXD stays high because LIN is high.
On the board the LIN pin is assembled with a 220pF capacitor to ground. Additionally, the two extra components diode D2
(LL4148) in series with resistor R3 (1k
) required for using the development board for a LIN master application have
designated placeholders for convenient mounting.
1.2.2
Input/Output Pin (TXD)
In normal mode the TXD pin is the microcontroller interface for controlling the state of the LIN output. TXD must be low in
order to have a low LIN bus (dominant state). The TXD pin has an internal pull-down resistor. If TXD is high, the LIN output
transistor is turned off and the bus is in the recessive state. If TXD is low, the LIN output transistor is turned on and the bus
is in the dominant state.
An internal timer prevents the bus line from being driven permanently in the dominant state. If TXD is forced to low longer
than t
DOM
> 27ms, the LIN pin is switched off (recessive mode). To reset this mode, TXD needs to be switched to high
(>10µs) before switching LIN to dominant again. This feature is disabled in the ATA6664, meaning this device is able to send
a static low to the bus and is therefore highly suitable for very low data rates.
During fail-safe mode the TXD pin is used as an output and signals the wake-up source if an external pull-up resistor is
connected. The TXD output transistor is current limited to <8mA.
1.2.3
Output Pin (RXD)
This pin reports the state of the LIN bus to the microcontroller. LIN high (recessive state) is indicated by a high level at RXD,
LIN low (dominant state) is indicated by a low level at RXD. The output is an open drain, therefore it is compatible with a 3.3V
or 5V power supply. The output is short circuit protected.
Please note that the ATA6663/ATA6664 has to be in normal mode in order to have the communication via LIN enabled.
After a wake-up the device is in fail-safe mode and the RXD pin switches to low in order to interrupt the microcontroller.
