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# The maximum DRVDD current (IDRVDD) of AD9251

Hi Teams,

I`d like to know the maximum value of IDRVDD for AD9251. the data sheet page26 indicated as below: IDRVDD = VDRVDD × CLOAD × fCLK × N where N is the number of output bits (30, in the case of the AD9251), the clock of my design is 4MHz, if following this formula, if assumed the CLOAD is 5pF,  IDRVDD_max is about 3.3V*5pF*4MHz*30=1.98mA, am I right? would you please confirm this calculated result? in addition there had the description "In some applications, it may be acceptable to drive the sample clock inputs with a single-ended 1.8 V CMOS signal. In such applications, drive the CLK+ pin directly from a CMOS gate, and bypass the CLK− pin to ground with a 0.1 μF capacitor (see Figure 54). "  what is the scenario of using a single-ended 1.8 V CMOS signal for the CLK input?

[edited by: ShawnTiger at 6:16 AM (GMT -4) on 18 Apr 2022]
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• the equation above is more like a typical value. for a max value (considering PVT) you can add a 20% multiplier, or about the same ratio from TYP to MAX as the AVDD current.

for single ended clock see figure 54

• Hi UmeshJ,

• What is the pre-condition of using the single-end clock input for AD9251?
• Is the single-end clock only 1.8V level? if yes, is it because the clock input use the 1.8V AVDD?
• The single-end clock is a 3.3V signal in my design, in this scenario the 3.3V single-end clock connect to AD9251 via a 0.1uF AC couple capacitor, no need any other external terminations same to as the figure 54, am I right?

Br,

Shawn Li

• Hi UmeshJ,