Rainbow Electronics ATA6664 - Manual (Page 4)

4
9146E–AUTO–03/11
Atmel ATA6663/ATA6664
3.7 Output Pin (RXD)
This pin forwards information on the state of the LIN bus to the microcontroller. LIN high
(recessive) is indicated 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 by a pull-up resistor of 5k
Ω
to 5V and a load capacitor of
20pF. The output is short-current protected. In unpowered mode (V
S
= 0V), RXD is switched
off. For ESD protection a Zener diode with V
Z
= 6.1V is integrated.
3.8 Enable Input Pin (EN)
This pin controls the operation mode of the device. If EN = 1, the device is in normal mode,
with the transmission path from TXD to LIN and from LIN to RXD both active. At a falling edge
on EN, while TXD is already set to high, the device switches to sleep mode and transmission
is not possible. In sleep mode, the LIN bus pin is connected to V
S
with a weak pull-up current
source. The device can transmit only after being woken up (see Section 3.9 , “Inhibit Output
Pin (INH)” ).
During sleep mode the device is still supplied from the battery voltage. The supply current is
typically 10µA. The pin EN provides a pull-down resistor in order to force the transceiver into
sleep mode in case the pin is disconnected.
3.9 Inhibit Output Pin (INH)
This pin is used to control an external voltage regulator or to switch on/off the LIN Master
pull-up resistor in case the device is used in a Master node. The inhibit pin provides an internal
switch towards pin V
S
which is protected by temperature monitoring. If the device is in normal
or fail-safe mode, the inhibit high-side switch is turned on. When the device is in sleep mode,
the inhibit switch is turned off, thus disabling the voltage regulator or other connected external
devices.
A wake-up event on the LIN bus or at pin WAKE will switch the INH pin to the V
S
level. After a
system power-up (V
S
rises from zero), the pin INH switches automatically to the V
S
level.
3.10 Wake-up Input Pin (WAKE)
This pin is a high-voltage input used to wake-up the device from sleep mode. It is usually
connected to an external switch in the application to generate a local wake-up. A pull-up cur-
rent source with typically –10µA is implemented. The voltage threshold for a wake-up signal is
3V below the VS voltage with an output current of typically –3µA.
If a local wake-up is not needed in the application, pin WAKE can directly be connected to pin
VS.
3.11 Operation Modes
1. Normal Mode
This is the normal transmitting and receiving mode. All features are available.
2. Sleep Mode
In this mode the transmission path is disabled and the device is in low-power mode.
Supply current from V
Batt
is typically 10µA. A wake-up signal from the LIN bus or via
pin WAKE will be detected and will switch the device to fail-safe mode. If EN then
switches to high, normal mode is activated. Input debounce timers at pin WAKE
(t
WAKE
), LIN (t
BUS
) and EN (t
sleep
,t
nom
) prevent unwanted wake-up events due to auto-
motive transients or EMI. In sleep mode the INH pin remains floating.