Original question:
Hi support:
When my board use ITECH as power source, the DAC8718 can out -7.5 - 7.5v, but i change to common power source.the DAC8718 output 0-15v
and my goal is that DAC8718( Dual-Supply) can out put -7.5 -7.5 v. the schematic as follow. common power is measured by oscilloscope is normal .
Hi:
Accord to the DAC8718 user manual ,the dac offset register's default value is 39322 , but when using different power , value of the offset pin is measured different. and then I write initial value to the offset register at startup of dac, the problem is solved.
But then another issue occur to me that the dac value measured by oscilloscope is sine scope ,the picture is showed as follow:
I don't know why? the DAC work mode is asynchronous and correction engine is off.
Hello,
Is the second power supply following the power-on reset sequencing given in the datasheet:
It is likely that some initializations are not being done correctly when the second power supply is used. There is a similar thread here: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/691710/dac8718-dac8718-power-supply-problem.
Can you compare the power up sequence of your two power supplies?
Best,
Katlynne Jones
Hi Katlynne：
Now I modify the peripheral circuit and satisfy the power-on reset sequencing,as follow.
but the sine wave(approximate 100k ) also exits, and offset pin 's voltage measured by oscilloscope and multi-meter is right.
test point is the DAC8718 dacx(x is 0-7),and I already break out any circuit that wired with the dacx pin before.
I use the multi-meter to measure the dacx ,the value is our expexction.
so why the DAC_X output value include the high frequency interference.
Hello,
This oscillation could be coming from the 100nF capacitors you have on the OFFSET A and B outputs, or the reference input. When you measured the voltage at offset A and B, did you see any oscillation there? It looks like the capacitive load stability of the analog outputs is 500pF. Adding the 100nF capacitors there might be causing the oscillations. Can you try removing these and then checking the DAC outputs?
Best,
Katlynne Jones
