U6812B Просмотр технического описания (PDF) - Atmel Corporation

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U6812B

Single-ended Bus Transceiver with Triple Buffer

Atmel Corporation 

Functional Description

K-interface

Open-collector Driver

OUTx

Power Supply

The K-interface is equipped with a 40-mA open-collector driver. The current is deter-

mined by the external pull-up resistor. The saturation voltage is below 0.6 V.

The open-collector output is protected by a 28-V Z-diode. The collector current is per-

manently monitored for short circuits via a built-in shunt. In the event of a short circuit

occurring at VBatt, the collector current is held at approximately Icreg = 80 mA; the chip

temperature then rises due to power loss. This status is maintained until the detection of

overtemperature which causes the K-line output to be disabled and stored to memory.

The internal short-circuit detection threshold is Isc > 0.8 ´ Icreg. The output remains dis-

abled until a falling edge of a pulse is available to its input. Any further attempt to

connect while the short circuit is still present causes the above sequence to be

repeated. The output can be activated normally once the short circuit has been

removed. The maximum baud rate is 250 kBaud.

The K-line allows bi-directional communication with the microcontroller. When the out-

put K is disabled, information can be transferred to the processor via the input

comparator at pin RxD.

The digital output RxD is a push-pull output stage with a driver power of 1 mA.

In the event of a line break at the K-line, the output K is connected to GND via the built-

in 85-kW pull-down resistor, thus allowing the microcontroller to detect this fault. The

maximum sampling frequency is 250 kBaud.

The outputs are designed for a maximum static current of 40 mA, which is determined

by the external pull-up resistor. The saturation voltage is below 0.6 V

The three OUTx-driver outputs are activated with "active low" at the corresponding

input. Outputs OUT2 and OUT3 can also be disabled with "active low" at the disable

input, regardless of their input signal. The outputs are released by an open disable input

or by using high potential.

The open-collector outputs are connected to a 28-V Z-diode. The collector current is

permanently monitored via a built-in shunt circuit to permit the detection of short circuits.

If a short circuit occurs at VBatt, the collector current is held at approximately

Icreg = 80 mA; accompanied with a rise of chip temperature due to power loss. This sta-

tus is maintained until the detection of overtemperature which causes the output

affected by the short circuit to be selectively disabled and stored to memory. The inter-

nal short-circuit detection threshold is Isc > 0.8 ´ Icreg. The affected output remains

disabled until a falling edge of a pulse is available to its input. Any further attempt to con-

nect while the short circuit is still present causes the above sequence to be repeated.

The output can be activated normally once the short circuit has been removed.

The IC must be equipped with external RC circuitry to limit the voltage in the event of

power surges (see Figure 3 on page 3). This prevents the circuit from being damaged or

destroyed, and provides a buffer in case of power fluctuations at VBatt. The RxD compar-

ator is powered via pin VS, producing its reference voltage of 1/2 VS, while all other

blocks are supplied via VCC.

The operating voltage can vary between VS= 7 V and 26 V. The resistor R1 at pin VS lim-

its the current via the built-in 28-V Z-diode between VS and GND.

4 U6812B

4760A–AUTO–10/03

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