ISO3082: Dual Isolated Half-Duplex RS-485 Repeater (TIDA-00333)

Part Number: ISO3082

Hi Isolation Team,

One of my customers is using a pair of ISO3082s in a dual isolated repeated configuration based on the TIDA-00333 design. No issues whatsoever when driving the RS-482 bus from low to high (D 0 to 1). However, when driving the bus high to low (D 1 to 0), a slight delay in the B output (pin 13) with reference to A causes a "knee" in the Va - Vb curve. 

Couple of things:

1. After driving the bus high, the transceiver is switched to Hi-Z mode and the bus remains high via the fail-safe resistors. So,when driving the bus high-to-low,the driver transitions out of Hi-Z mode. I noticed on the datasheet slightly different propagation delays when transitioning from Hi-Z to high and low level (see below). Is this the culprit on the time delay between output A and B? What would be the effect in the downstream receiver? Any suggestions on how to minimize this delay? 

2. What would be the effect of increasing Rd in the timing control scheme? 

Thanks,

Leo Rodríguez

Analog Field Applications - Waltham, MA

3 Replies

  • Hi Leo,

    You mentioned a slight delay in the B output with respect to A. Could you please let me know how much this delay is?
    If possible attach a waveform captured on the board?
    Is the same delay seen when driving from (A1,B1) and (A2,B2)? The reason for the difference between A and B looks like some asymmetry in the bus line (A with respect to B).

    Regards,
    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Hi Anand,

    The delay of B with respect to A is approximately 1us . Unfortunately, I cannot include the waveform or schematic, given that they are proprietary information. As of now, we're verifying if a similar behavior is observed in the other device. Have you seen such a delay before?

    Regards,
    Leo
  • In reply to Leo Rodriguez:

    Query was further discussed over email.

    Regards,
    Anand Reghunathan