AN2482

Unisolated AS-interface bus application

11/18

3.3

Un-isolated connection of the PCLT with AS-Interface

controller

To remove the opto-coupler in lower cost versions, the operation of the PCLT has been

extended to fit the AS-Interface application. A precaution is required on its interface with the

bus controller: the impedance between the two circuits must be high in order to maintain the

isolation.

generated with a Zener diode reference fed from the sensor bus.

Because of the buffer voltage increase, it becomes possible to insert a high impedance

between the PCLT output and the AS-Interface bus controller input. Typically a 100 k

Ω

resistor is designed while keeping a 5 V CMOS operation on the input of the bus controller.

Figure 12. shows the application diagram where the PCLT is connected to the slave bus

controller through a 100 k

Ω resistor. The logic signal is transmitted with a low level of less

defined by the voltage drop across the 100 k

Ω pull down resistor. (35 µA times 100 kΩ).

Figure 12.

Un-isolated AS-Interface slave controller unit using the PCLT

10

12V

SLAVE AS-I

CTRLER

V

CC

28V

1

PCLT

750Ù

7

14

9

V

CCsensor

sensor

Vreg

ASiP

ASiN

30V

10

12V

SLAVE AS-I

CTRLER

V

CC

28V

1

PCLT

750Ù

7

14

9

V

CCsensor

sensor

Vreg

ASiP

ASiN

30V