Rainbow Electronics ATA6626 - Manual (Page 3)

3
4970A–AUTO–01/07
ATA6621/22/24 Development Board
As the window watchdog of the ATA6621/22/24 is already active in the Pre-normal mode (Fail
Safe mode), a periodic reset signal will be generated at the pin NRES as long as no trigger
signal can be received at the watchdog trigger input. Normally the connected microcontroller
will be monitored by the watchdog, so it has to generate the required trigger signal as
described in
Section 2.3 on page 4 and in more detail in the datasheet of the corresponding
device. For the quick start it is sufficient to generate a square-wave signal with V
PP
= VCC and
f = 75Hz at pin NTRIG or PTRIG for the ATA6621 or with f = 50Hz at pin NTRIG for the
ATA6622 and ATA6624 (this is recommended only for testing purposes). In order to check
that the watchdog is triggered in the expected way, the reset pin NRES can be monitored until
a continuous high level is available.
Please note that the communication is still inactive in Pre-normal mode (Fail Safe mode).
In order to communicate via the LIN bus interface you have to switch to normal mode by
applying the VCC voltage (5V or 3.3V, as appropriate) at pin EN.
2. Hardware Description
In the following sections only the normal operating conditions will be described. For further
information concerning one of the mentioned features, refer to the corresponding datasheet.
2.1 Power Supply (VB and GND)
In order to get the development board running, an external 5.7V to 18V DC power supply is
required between the terminals VB and GND. The input circuit is protected against
inverse-polarity with the protection diode D1, so that there is normally a difference between
the VB and VS level of approximately 0.7V.
2.2 Voltage Regulator (PVCC and VCC)
The internal 5V/3.3V voltage regulator is capable of driving loads with up to 50 mA current
consumption so the SBCs are able to supply a microcontroller, sensors and/or other ICs. The
voltage regulator is protected against overloads by means of current limitation and overtem-
perature shutdown. To boost the maximum load current, an external NPN transistor may be
used, with its base being connected to the VCC pin and its emitter connected to PVCC. If this
is done, the regulated output voltage of 5V or 3.3V is available at pin PVCC. For this reason,
the pin PVCC and not the pin VCC is led to the connector available off the board.
But in normal operation, the pins PVCC and VCC have to be connected directly. This is done
by setting jumper J1.
Table 1-4. ATA6624
Mode VCC WD_OSC TEMP INH RXD LIN Transceiver
Fail Safe mode 5V 1.23V - On 5V Recessive Off
Normal mode 5V 1.23V - On 5V Recessive On