ATA6620N 데이터 시트보기 (PDF) - Atmel Corporation

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ATA6620N

LIN Bus Transceiver with Integrated Voltage Regulator

Atmel Corporation 

ATA6620N

4.4 Unpowered Mode

If battery voltage is connected to the application circuit (see Figure 4-7), the voltage at the VS

pin increases due to the block capacitor. When VS is higher than the VS undervoltage threshold,

VSth, the IC-mode changes from Unpowered to Pre-normal mode. The VCC output voltage

reaches nominal value after tVCC. This time depends on the VCC capacitor and the load.

NRES is low for the reset time delay tReset; no mode change is possible during this time.

Figure 4-7. VCC Voltage Regulator: Ramp Up and Undervoltage

VS

12V

5.5V

3V

VCC

5V

Vthun

NRES

tVCC

tres

tes_f

5V

5. Fail-safe Features

• During a short circuit at LIN, the output limits the output current to IBUS_LIM. Due to the power

dissipation, the chip temperature exceeds tLINoff and the LIN output is switched off. The chip

cools down and after a hysteresis of thys, switches the output on again. During LIN

overtemperature switch-off, the VCC regulator works independently.

• There are now reverse currents < 3 µA at pin LIN during loss of VBatt 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 IVCCn. Because of

undervoltage, NRES switches to low and sends a reset to the microcontroller. The IC

switches into Pre–normal mode. If the chip temperature exceeds the value tVCCoff, the VCC

output switches off. The chip cools down and after a hysteresis of thys, switches the output on

again. Because of Pre-normal mode, the VCC voltage will switch on again although EN is

switched off from the microcontroller.The microcontroller can then start with normal

operation.

• Pin EN provides a pull-down resistor to force the transceiver into recessive mode if EN is

disconnected.

• Pin RXD is set floating if VBatt is disconnected.

• Pin TXD provides a pull-up resistor to force the transceiver into recessive mode if TXD is

disconnected.

11

4850I–AUTO–09/09

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