| SLA Status | Assignee | Support Status |
|---|---|---|
| SLA Closed. | ericb |
Awaiting Customer Response |
LTC4332
Recommended for New Designs
The LTC4332 is a point-to-point rugged SPI extender designed for operation in high noise industrial environments over long distances. Using a ±60V fault...
Datasheet
LTC4332 on Analog.com
Hello everyone,
I have an issue with LTC4332 SPI extender regarding remote INT duration. I use extender with the remote device which generates 20us pulse when the interrupt occurs, but sometimes it is not passed to local side (Fig1). I've attached several scope screenshots where this manifestation can be observed. I also use LTC4332 in other application where INT is active until the data is read, and that works perfectly.

Fig1. Interrupt generated on remote side, but isn't transferred to local

Fig2. Delay between remote and local

Fig3. Delay between remote and local

Fig4. Remote interrupt not transferred to local
Hi Miodrag,
Absent any SPI traffic, the INT input on the LTC4332 is periodically sampled based on the link heart beat refresh which is based on the speed configuration settings. When there is SPI traffic, the INT is sampled at the start of the transaction and then again after the transaction completes when a heartbeat occurs again. The LTC4332 assumes that once asserted the INT would remain asserted until the SPI controller responds to the target device asserting the INT.
In order to assure that the INT is observed, it will need to be held down long enough for at least one heartbeat refresh to occur. I've measured the heartbeat period for the different speed index values using some eval boards on the bench:
| Speed Index | LTC4332 |
| 0 | 845 us |
| 1 | 679 us |
| 2 | 340 us |
| 3 | 255 us |
| 4 | 171 us |
| 5 | 84 us |
| 6 | 43 us |
| 7 | 22 us |
| 8 | 11 us |
Depending on the selected speed, you'll want to make sure that your INT is held down longer than the above times.
Eric