• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 34 subscribers
  • Views 151 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

SN65CML100: power consumption

SN65CML100: SM65CML100 current consumption

Cyril Garric
Prodigy 20 points

Part Number: SN65CML100

Hello,

My concern is about the current consumption of the SN65CML100. It is given for 9 to 12 mA max in its datasheet. But I measured it on its evaluation module at 24.17 mA dc.

I did my measurement with:

  • grounded inputs 
  • floating outputs
  • J3 - Vcc1 (pin 5 of the chip, GND) tied to GND

I would like to understand. Please could you point out what's wrong in my measurement?

Thx a lot !

  • 0
    TI__Genius 14966 points

    Hi Cyril,

    Are you using the official EVM from this page without any modifications? https://www.ti.com/tool/SN65CML100EVM 

    Can you share the supply voltage you are applying to Vcc? Also, pin 8 is Vcc, not pin 5. Can you confirm you are using the right pins and how are you measuring the supply current into pin 8 of the device? 

    Regards,

    Matt

  • 0
    Prodigy 20 points

    Hi Matt,


    Thank you for the reply. 

    • Yes I confirm I used the official EVM SN65CML100EVM, that I bought from Digikey (296-20537-ND). 
    • I did 2 changes: 
      • I tied J3 to GND to connect the pin 5 of the chip to GND.
      • I removed C1, C2, C6 and C7 (the bulk capacitors on the power rails).
    • I powered the EVM with a nice stable and quiet 3.3Vdc from a bench power supply.
    • I measured the mean current using a 6.5 digits ammeter in series with the PSU.

    The jumper JMP2 was present, (tying the pin 4 of the chip to GND).

  • 0 in reply to Cyril Garric
    TI__Genius 14966 points

    Hi Cyril, 

    VBB (pin 4) is a reference voltage output of the device, and it is to be used to bias LVPECL inputs when R5 is populated. If you are tying this pin to GND, you are probably drawing additional current out of that pin. You should leave this pin floating if you are not using it. 

    Also in this EVM, J2 is the EVM GND, J3 is the DUT GND, and J1 is Vcc. It doesn't seem that you have the proper power/ground connections for this board. Please refer to Figure 2-2 in the user guide (see below) and adjust your connections accordingly. 

    Regards,

    Matt 

  • 0 in reply to Matt Smith
    Prodigy 20 points

    Thank you Matt,

    When I said that pin 4 was tied to GND with JMP-2, that was incorrect. This jumper actually connects a decoupling capacitor (C12 from the EVM) to pin 4; it does not short the pin to GND. Sorry for the confusion. And the board was powered exactly as you indicated, except that “Power Supply 2” was set to 0 V. 

    Finally, I added two 51 Ω termination resistors (R2 and R3) to GND to the chip outputs, and the current consumption decreased to 16 mA. That is way better than the original 24 mA, but still higher than specification (9 mA to12 mA).

    Thank you again for your support, Matt. Now I know why I got it wrong.