DS90LT012AH: SPI to LVDS Ribbon Cable Impedance Matching

Part Number: DS90LT012AH
Other Parts Discussed in Thread: TPD1E01B04, TPD4E05U06-Q1, DS90LT012A, DS90LV012A, ESDS312,

Hi there.

My MCU uses 10MHz SPI signaling that I’d like to convert to LVDS over two expander ports to reduce EMI and maintain signal integrity.

I’m looking to use DS90LT012AHMF/NOPBTR-ND and DS90LV011AHMF/NOPB drivers/receivers to do so and was wondering if cable and connector type might be an issue. The datasheets mention that 100 ohm impedance is to be maintained through the transmission line, though I’m finding it difficult to find cables and mating connectors rated for wide temperature ranges that fit the bill.

Will a standard ribbon cable suffice? The DS90LT012 has a 100 ohm termination resistor built in, so is that good enough for the distances I’m dealing with?

Also, what TVS diodes do you recommend for these DS90LTs? I see TPD1E01B04 & TPD4E05U06-Q1 recommended on your website, though I’d like to use a larger package (easier to solder).

Apologies for the crude diagram.

Thanks,

over 3 years ago

+1 Ikechukwu Anyiam over 3 years ago

TI__Mastermind 35130 points

Hi Al,

Ribbon cable is generally okay for short distances (< 0.5 m). You may want to consider using the DS90LV012A and an external termination resistor instead of the DS90LT012A, as the transmission media must be terminated to its characteristic impedance to prevent reflections (which may not be the internal 100-ohm of the DS90LT012A).

For TVS diodes I'll move this thread to another section for recommendations.

Regards,

I.K.

+1 Matt Smith3 over 3 years ago

TI__Expert 8486 points

Hello Al,

If you're wanting to protect a 3 V LVDS receiver, I would recommend ESDS312 for a bigger package. This device comes in a SOT23 package, same as the DS90LT012AH. However, be aware that this device has a much higher capacitance than TPD1E01B04 (2.3 pF vs 0.18 pF).

Regards,

Matt Smith

0 Al over 3 years ago

Prodigy 40 points

Thanks.

+1 Al over 3 years ago in reply to Matt Smith3

Prodigy 40 points

I also have some 5V and GND lines on the ribbon cable and would like to protect them too. Would a TVS diode with a 5.5 Vrwm device suffice and should it be bi-directional or is uni-directional fine?

Thanks,

Al.

+1 Matt Smith3 over 3 years ago in reply to Al

TI__Expert 8486 points

Yes you can use a 5.5 V Vrwm diode to protect the 5 V line. If the normal operating voltages on that line do not go below 0 V, then I would use a unidirectional device. The GND pin should be fine without a diode.

Regards,

Matt Smith

0 Al over 3 years ago in reply to Matt Smith3

Prodigy 40 points

Thanks

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DS90LT012AH: SPI to LVDS Ribbon Cable Impedance Matching