DS90LV048A: Reference resistor value ???

Poh Kok Keng

Part Number: DS90LV048A
Other Parts Discussed in Thread: DS90LV012A, SN74LVC1G04

Tool/software:

customer already study the app note (snla051c.pdf) for external biasing for failsafe.

But they are not able to figure out the reference resistor value.

Is there a reference resistor value for below circuit to be used together with DS90LV012ATMF to order to get a output LOW output during fail-safe?

Best Regards,

kpk

2 months ago

0 Clemens Ladisch 2 months ago

Guru 290950 points

To output low, both the DS90LV012A and the DS90LV048A require a differential input voltage of less than −100 mV.

R_T is 100 Ω, so the current must be more than 0.1 V / 100 Ω = 1 mA. With R₁ = R₃ = 1.2 kΩ, the current would be 3.3 V / (1.2 kΩ + 100 Ω + 1.2 kΩ) = 1.32 mA.

Please note that if the two signal lines are shorted together, then the differential input voltage is 0 V, and the receiver outputs high; no resistor can change that. An alternate solution to get a fail-safe low value would be to remove R1/R3, exchange the +/− inputs, and add an inverter (e.g., SN74LVC1G04).

0 Sean Guo 2 months ago

TI__Mastermind 20890 points

Hi Poh,

Please expect a delay due to the US holiday, our expert supporting this device will get back to you next week.

Regards,

Sean

0 Amy 2 months ago

TI__Genius 15321 points

Hello,

Please refer to this post with another interested in this application: DS90LV048A: Output LOW on Fail-safe - LVDS Rx

Here is another good reference on this topic: AN-1194 Failsafe Biasing of LVDS Interfaces (Rev. C) (ti.com)

Sincerely,

Amy

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DS90LV048A: Reference resistor value ???