13
4986F–AUTO–07/08
ATA6622/ATA6624/ATA6626
5.5 Fail-safe Features
• During a short-circuit at LIN to V
Battery
, the output limits the output current to I
BUS_LIM
. Due to
the power dissipation, the chip temperature exceeds T
LINoff
, and the LIN output is switched
off. The chip cools down and after a hysteresis of T
hys
, switches the output on again. RXD
stays on high because LIN is high. During LIN overtemperature switch-off, the VCC regulator
works independently.
• During a short-circuit from LIN to GND the IC can be switched into Sleep or Silent Mode. If
the short-circuit disappears, the IC starts with a remote wake-up.
• The reverse current is very low < 15 µA at the LIN pin during loss of V
Batt
or GND. This is
optimal behavior for bus systems where some slave nodes are supplied from battery or
ignition.
• During a short circuit at VCC, the output limits the output current to I
VCCn
. Because of
undervoltage, NRES switches to low and sends a reset to the microcontroller. The IC
switches into Fail-safe Mode. If the chip temperature exceeds the value T
VCCoff
, the VCC
output switches off. The chip cools down and after a hysteresis of T
hys
, switches the output on
again. Because of the Fail-safe Mode, the VCC voltage will switch on again although EN is
switched off from the microcontroller. The microcontroller can start with its normal operation.
• EN pin provides a pull-down resistor to force the transceiver into recessive mode if EN is
disconnected.
• RXD pin is set floating if V
Batt
is disconnected.
• TXD pin provides a pull-up resistor to force the transceiver into recessive mode if TXD is
disconnected.
• If TXD is short-circuited to GND, it is possible to switch to Sleep Mode via ENABLE after
t
dom
> 20 ms (only for ATA6622/ATA6624).
• If the WD_OSC pin has a short-circuit to GND or the resistor is disconnected, the watchdog
runs with an internal oscillator and guarantees a reset after the second NTRIG signal at the
latest.
5.6 Voltage Regulator
The voltage regulator needs an external capacitor for compensation and for smoothing the dis-
turbances from the microcontroller. It is recommended to use an electrolythic capacitor with
C > 10 µF and a ceramic capacitor with C = 100 nF. The values of these capacitors can be var-
ied by the customer, depending on the application.
The main power dissipation of the IC is created from the VCC output current I
VCC
, which is
needed for the application. In Figure 5-2 on page 14 the safe operating area of the
ATA6622/ATA6624/ATA6626 is shown.
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