SN65ELT22: TTL <-> Differential for SFP module

Iven Xu

Intellectual 2090 points

Part Number: SN65ELT22
Other Parts Discussed in Thread: SN65EPT23, SN65EPT22, DS90LV019

Dear Expert,

my customer would like to find a device to acheive TTL<-> differential function for SFP module, you can see below picture - from SFP datasheet:

1, now I found a device SN65ELT22/23, which looks the voltage range can meet the SFP voltage range requirement. could you please help check and comments?

2, customer do not want to use ETH PHY(support fiber), so we are looking for such kind of device, do you think it is ok for SFP?

3, expect SN65ELT22/23, do you think we have other parts can meet this requirement?

Best Regards

Iven Xu

over 6 years ago

0 Lee Sledjeski over 6 years ago

TI__Mastermind 43795 points

Hi Iven,

We have products which meet the electrical specifications. However, many SFP modules run at Gbps speed which is beyond what can be achieved with TTL I/O. What data rate is required for your application.

Regards,

Lee

0 Iven Xu over 6 years ago in reply to Lee Sledjeski

TI__Intellectual 2090 points

<50M

0 Yaser Ibrahim over 6 years ago in reply to Iven Xu

TI__Genius 10250 points

Hello,

SN65EPT22/23 may be more appropriate for this application since they are 3.3 V devices and support higher rates (while SN65ELT22/23 are 5V devices). We have seen these devices used with SFP modules before. However, the 2000 mV differential output from the RD exceeds the max limit of 1200 mV for the SN65EPT23 and there is potential for issues. I recommend attenuating the input signal to keep it below the datasheet limit.

Regards,
Yaser

0 Iven Xu over 6 years ago in reply to Yaser Ibrahim

TI__Intellectual 2090 points

Hi Yaser,

yes, that should be an problem for the 2000mV differential ouptut from the RD exceeds the max limit of 1200mV.

following question:

1, for your recommendation, how to attenatue the input signal out from the RD of SFP module?

2, is there any other device can handle this application?

Best Regards

Iven Xu

0 Lee Sledjeski over 6 years ago in reply to Iven Xu

TI__Mastermind 43795 points

Hi Iven,
The DS90LV019 has this function.
Regards,
Lee

0 Iven Xu over 6 years ago in reply to Lee Sledjeski

TI__Intellectual 2090 points

but DS90LV019 cannot meet the voltage range requirement.

0 Lee Sledjeski over 6 years ago in reply to Iven Xu

TI__Mastermind 43795 points

The LVDS "VOD" specification is not a peak to peak number, it is only the peak value. To arrive at a peak-to-peak amplitude you need to multiply by 2. The actual output amplitude of the LV019 is 500-900mV which fits into the module requirements.

Regards,
Lee

0 Iven Xu over 6 years ago in reply to Lee Sledjeski

TI__Intellectual 2090 points

Hi Lee,

for DS90LV019, I understood the Vod of the driver should be 500mV~900mV. which can meet the TD+- requirement (500~2400mV acceptable range for the SFP module.

but what's the input swing of the receiver? becuase the SFP RD+- output voltage range is 250mV~2000mV. does the receiver of DS90LV019 can handle this voltage range?

Best Regards

Iven Xu

0 Lee Sledjeski over 6 years ago in reply to Iven Xu

TI__Mastermind 43795 points

Hi Iven,
Yes the LVDS input can handle that voltage range.
Regards,
Lee

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SN65ELT22: TTL <-> Differential for SFP module