• Not Answered

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

2 Replies