SN65LV1023A: Serializer / Deserializer

Ray Vincent Aranzaso

Part Number: SN65LV1023A
Other Parts Discussed in Thread: SN65LV1224B, , TRS3232

Hi,

Good Day. Customer is working with SN65LV1023A and SN65LV1224B. Please see below his query for your reference. Thank you very much.

I need help selecting an IC for converting multiple RS232 signals and passing it through to an SFP, I understand I can use the TRS3232 for converting 232 into LVTTL by supplying it with 3.3V, but I need help selecting the proper serializer / deserializer IC.

I am concerned that the RS232 signals will not be fast enough for the Serializer IC to confirm there's good data?

I was looking at one like SN65LV1023ADB and SN65LV1224B for deser.

I essentially just want to convert 4 - 8 RS232 signals into an SFP+ so if there's another solution I'd be open to that.

Best Regards,

Ray Vincent

over 4 years ago

0 Nasser Mohammadi over 4 years ago

TI__Guru* 93570 points

Hi Vincent,

SN65 parts you noted should be able to do the job. RS232 signals typically run at 115.2kbps. As long as we over sample these at least at twice the highest frequency we should be fine. Another benefit of the part you noted is pin compatibility with DS92 parts.

Regards,,Nasser

0 Ray Vincent Aranzaso over 4 years ago in reply to Nasser Mohammadi

TI__Mastermind 18180 points

Hi Nasser,

Good Day. Please see below the response of our expert to your query. Thank you very much.

It's a good solution to use the SN65 but I have concerns over the termination load 100 ohm? I see in the datasheet that it will be near the maximum Vod for SFP+ (see figure 2) 850mV is typically the SFP+ maximum Vod, the chart here is showing just below 800mV typical Vod. The SFP+ is terminated internally with RL = 100ohm, is there going to be a problem with that since it's very close to the maximum rating? Do I just select RL at the SN65 pins to be lower than 100 ohm or is that not proper?

Do you have any example circuits that I could use for implementing this chip into my design? That'd be great as I have never used SERDES chips before.

Best Regards,

Ray Vincent

0 Ray Vincent Aranzaso over 4 years ago in reply to Nasser Mohammadi

TI__Mastermind 18180 points

Hi Nasser,

Good Day. Another query from the customer. Please see below. Thank you very much.

What is the benefit of the DS92, I was assuming that I can just put LVTTL into the SN65? I wouldn't need LVTTL to LVDS conversion since the SN65 handles this already? I need to squeeze all my LVTTL signals into a single serial link to the SFP+

Best Regards,

Ray Vincent

0 Nasser Mohammadi over 4 years ago in reply to Ray Vincent Aranzaso

TI__Guru* 93570 points

Hi Ray Vincent,

1). I am thinking perhaps you can use a passive attenuation pad to bring down 800mV output swing. Majority of SFPs use 100-ohm differential impedance so we should match this impedance. Please note link below where you can find some of these passive attenuators:

https://www.rfcafe.com/references/calculators/attenuator-calculator.htm

2). DS92 pin compatibility allows more availability of the part - that's what i was thinking.

Regards,,Nasser

0 Ray Vincent Aranzaso over 4 years ago in reply to Nasser Mohammadi

TI__Mastermind 18180 points

Hi Nasser,

Good Day. Please see below another query for from the customer. Thank you very much.

I was wondering still if there's an common application circuit diagram for the SN65 chips? I'm just not completely sure about the clock and sync pins. Do you have anything like that?

Best Regards,

Ray Vincent

0 Nicholaus_Malone over 4 years ago in reply to Ray Vincent Aranzaso

TI__Mastermind 27935 points

Hi Ray,

Nasser is out until Tuesday, I will help support until he returns. Please give me a moment to look for this and I will get back to you ASAP.

Regards,

Nicholaus

0 Nasser Mohammadi over 4 years ago in reply to Nicholaus_Malone

TI__Guru* 93570 points

Hi Ray Vincent,

I checked and cannot find application circuit. These are mature and older products. Please refer to the data sheet.

Regards,,Nasser

0 Ray Vincent Aranzaso over 4 years ago in reply to Nasser Mohammadi

TI__Mastermind 18180 points

Hi Nasser,

Good Day. Please see below the response of our customer to your reply. Thank you very much.

Actually I ended up finding something, it's this link here

https://www.ti.com/lit/an/slla116/slla116.pdf?ts=1647867283241

I still need help selecting the attenuation on the Receiver of SFP+, It's internally terminated with 100 ohm so if I just place 100 ohm on my LVDS line in parallel it should view as 50 ohm to the SN65?

Best Regards,

Ray Vincent

0 Ray Vincent Aranzaso over 4 years ago in reply to Nicholaus_Malone

TI__Mastermind 18180 points

Hi Nicholaus, Nasser,

Good Day. I would like to follow up about the customer's query. Thank you very much.

Best Regards,

Ray Vincent

0 Nasser Mohammadi over 4 years ago in reply to Ray Vincent Aranzaso

TI__Guru* 93570 points

Hi Ray Vincent,

Please follow rfcafe link that was sent earlier. SN65 needs to see 100-ohm. Your attenuation block needs to have 100-ohm on its input - facing SN65 . This means for 3dB attenuation - 70% or close to 600mV - you need Tee Attenuator 8.61 ohms R and chance 141 to close to 296 ohm. The same 8.61 ohms R go to to the negative side as well.

Regards,,Nasser

0 Ray Vincent Aranzaso over 4 years ago in reply to Nasser Mohammadi

TI__Mastermind 18180 points

Hi Nasser,

Good Day. Please see below the latest response of our customer to your reply. Thank you very much.

I had to order pcbs asap so I went with just a termination of 1 resistor between LVDS. I made the trace impedance 50 ohms and was hoping that putting 100 ohm in parallel will make it 50 ohm total and reducing the output swing. thanks if you know this is bad please let me know before blowing up anything.

Best Regards,

Ray Vincent

0 Nasser Mohammadi over 4 years ago in reply to Ray Vincent Aranzaso

TI__Guru* 93570 points

I don't think this will blow up the part. However, from signal integrity point of view this may not be optimum. I expect signal level would be attenuated.

Regards,,Nasser

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SN65LV1023A: Serializer / Deserializer