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AM3874 VREF SSTL_DDR[x]

Michi Yama
Guru 10030 points
Other Parts Discussed in Thread: AM3874

Hi,

I ahve one question regarding VREF SSTL_DDR[x] of AM3874.

According to the schematics of EVM, half voltage of VDDQ_1V5 is supplied to VREF SSTL_DDR[0]. VDDQ_1V5 is divided by  two 1kohm(+-1% ) resistors.

In the datasheet, the sink current value of VREF SSTL_DDR[0] is not written. Is EVM schematic for VREF SSTL_DDR[0] is satisfied AM3874 spec?

Please advise me.

Best regards,

Michi 

 

  • 0
    TI__Genius 11470 points

    Hello,

    There is no exact answer to what is the value of the sink current, but I think that the EVM schematic is fully operational. The value of the sink current should be insignificant enough to not affect the accuracy of the divider (with 2x1kOhm (+/- 1%) resistors).

    Thank you.

    BR

    Vladimir

  • 0 in reply to Vladimir-XID
    Guru 10030 points

    Dear Vladimir-san,

    Thank you for your reply. It is very helpful for us.

    But we need more information.

    As you know, VREFSSTL_DDR[x] is connected to divided "DVDD_DDR" (VDDQ_1V5) by 1kohm resistor. Same "Vref" is used for DDR3 memory.

    Vref is connected to Vrefdq and Vrefca of DDR3 memory. According to the Micron data sheet, the inpurt leakage current of the vref pin is +/- 2uA.

    How about VREFSSTL_DDR[x] of AM3874? Is it no effect for very small current? Does the schematic of TI EVM keep 0.75V even though bothe

    device AM3874 and DDR3 are conneced?

    Please advise me again.

    I appreciate your quick reply.

    Best regards,

    Michi

  • 0 in reply to Michi Yama
    TI__Genius 11470 points

    Hi Michi,

    Michi Yama said:

    Does the schematic of TI EVM keep 0.75V even though bothe

    device AM3874 and DDR3 are conneced?

    The EVM board has been in production for quite some time now and it seems there are no issues with that one; so it should be OK, we guess. Please, read "VREFSSTL_DDR Routing" section in the device datasheet, that is what is documented.

    Thank you.

    BR

    Vladimir