slightly OT q. for BDLC experts

Started by ctrobot28 October 1, 2003

I'm using an MC33390 transceiver between the 9S12DP256 and the J1850
bus. The datasheet for the 33390 shows a recommended application
circuit, with a 25V MOV (varistor) across the output. But it also
specifies an output capacitance of 470 pf. I cannot find a MOV with
that low a capacitance. So I'm wondering what others have done for
this. Would a zener of, say, 18V be sufficient there? What kind of
transients could happen on the bus? And, while I'm at it, is that
1000uf capacitor on the B+ input really necessary?



I used 10.7Kohm from pin 4 to pin 3. Then 470pF from pin 3 to
ground. Pin 4 to bus is a 47uH inductor. 470 ohm pin 6 to ground.

This seems to work. Although when I was looking at 33390 I didn't
see a varistor. Specs must have changed since I last check.

1000uF?? Didn't use it. --- In , "ctrobot28" <pdm@o...> wrote:
>
> I'm using an MC33390 transceiver between the 9S12DP256 and the
J1850
> bus. The datasheet for the 33390 shows a recommended application
> circuit, with a 25V MOV (varistor) across the output. But it also
> specifies an output capacitance of 470 pf. I cannot find a MOV with
> that low a capacitance. So I'm wondering what others have done for
> this. Would a zener of, say, 18V be sufficient there? What kind of
> transients could happen on the bus? And, while I'm at it, is that
> 1000uf capacitor on the B+ input really necessary?