slightly OT q. for BDLC experts | 68HC12

Join our technical discussions about Freescale Microcontrollers: M68HC12. (Freescale Semiconductor is a Subsidiary of Motorola).

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?

(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )

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?

(You need to be a member of 68hc12 -- send a blank email to 68hc12-subscribe@yahoogroups.com )

Sign in

Search 68hc12

Subscribe to 68hc12

68hc12 by Keywords

Ads

Discussion Groups

See Also

Discussion Groups | 68HC12 | slightly OT q. for BDLC experts

slightly OT q. for BDLC experts - ctrobot28 - Oct 1 13:25:00 2003

Re: slightly OT q. for BDLC experts - zeta_alpha2002 - Oct 1 14:38:00 2003