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AD5791 usage: Vout doesn't change

Question asked by Makethon on Dec 15, 2017
Latest reply on Dec 17, 2017 by Makethon

I'm trying to output the Vout from the 2nd pin of my AD5791, but I don't succeed to do that.

Could someone give me a hint to solve it?

 

I don't use the evaluation board for AD5791, and the circuit configuration is almost same as Figure 53. Typical Operating Circuit of the datasheet Rev. D, Page 26 of 28.

I'm using a breadboard to evaluate the AD5791.

VDD = +15 V

VSS = -15 V

VREFPF = VREFPS = +10 V  (With AD8676 as shown in Fig. 53)

VREFNF = VREFNS = -10 V  (With AD8676 as shown in Fig. 53)

VCC = IOVCC = +5 V

!LDAC = GND

!CLR = !RESET = 3.3 V

Logic Voltage = 3.3 V

10 uF and 0.1 uF decoupling capacitors are connected.

 

Here I show the sending signals and the output.

Ch1(Yellow) the output of the AD5791. the impedance of the probe is 1 Mohm.

D0 : SCLK (Ch2 Green is also SCLK)

D1 : !SYNK

D2 : SDIN

By above, I set the AD5791 to normal mode, BIN/2sC is BIN, RBUF is 1.

And then, I send bellow pattern, but the output voltage (Ch1, Yellow) doesn't change at all.

I'm using NI USB-7856R to generate above digital signal.

Could someone tell me how can I fix the problem?

 

And I have one more question.

The datasheet says that "If the RESET  pin is not used, it should be hardwired to IOVCC." on page 20.

But in my case, IOVCC is  5 V, and the maximum logic input is limited to 0.7IOVCC (3.5 V in my case) on page 4.

I tried to connect the !RESET pin to 5 V and 3.3 V, but the AD5791 didn't work well both.

Which is correct?

 

Thank you for your kind help.

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