I would like to know "VREFSSTL_DDR(VREF) " current spec of AM3874.
I proposed customer to use TPS51200 as SINK/SOURCE DDR TERMINATION REGULATOR.
According to TPS51200 datasheet, REFOUT source current limit and sink current limit are 10mA(min.).
Who do you know the AM3874 VREFSSTL_DDR(VREF) current spec?
I would like to ask one more question regarding DDR3 Vtt.
As you know, Vtt is used for the termination of address and control signal. And address and control signal is driven by AM3874.
Rtt for termination resistor value is already specified in datasheet. But "Vtt min/max" value is not specified in AM3874 datasheet.
Customer said me "Vtt min/max" is needed to take the signal matching. Could someone give me "Vtt min/max" value for AM3874?
Customer can't design the system without this spec.
Please help !
The nominal value of the VTT supply is half the DDR3 supply voltage, and the min/max values can also be derived from the min/max values for the DDR3 supply voltage.
Please mark this Forum post as answered via the Verify Answer button below if it helps answer your question. Thanks!
The VREFSSTL_DDR(VREF) current is not specified separately, but the TPS51200 should work fine. The DM8168 EVM schematics are a good reference point for using the TPS51200.
Thank you for your reply.
Regarding DDR3Vtt, please let me know the meaning of you said that "the min/maxu values can also be derived from the min/max values for the DDR3 supply voltage.".
Are Vtt min/max values the same as the half value of DDR3 supply voltage min/max? Is AM3874 acceptable the fluctuation of the signal caused by Vtt value spec?
I appreciate your quick reply.
Yes, the Vtt min/max values are the same as half the value of DDR3 supply voltage min/max.
I talked your answer to my customer. They say there is no guarantee even though EVM works fine with TPS51200.
They can't understand the reason why VREF current is not specified. They say it should be specified if the block of the VREF(VREFSSTL_DDR) is unique than other IO pins. Pleasel let me know the VREFcurrent specification.
The below is the case of using TPS51200. Could you confirm it?
DDR3 supply voltage(VDDQ) is specified as the below.
VDDQ = 1.5V +- 0.075V
Based on your answer,
VTT = VDDQ / 2 = 0.75V +- 0.0375V ---> VTT requirement of AM3874. Tolerance is +- 37.5mV.
According to the datasheet of TPS51200, VO(VTT) of TPS51200 tolerance is +-25mV .
This value(+-25mV) satisfies AM3874's Vtt requirement.
Is this right?
Yes, that looks correct..
Thank you for your support.
You had given an answer to me regarding Vtt(min/max) value. I appreciate your support.
Please give me other question's answer. It is VREF current spec.
The below is my last post regading this question.
>Thank you for your reply.
>I talked your answer to my customer. They say there is no guarantee even though EVM works fine with TPS51200.
>They can't understand the reason why VREF current is not specified. They say it should be specified if the block of the VREF(VREFSSTL_DDR) is unique than other IO >pins. Pleasel let me know the VREFcurrent specification.
Your quick reply is helpful.
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