I'm using AD5593 in two projects.
One with 3V3 supply and one with 5V.
I use VREF link to VDD.
Is there a way to protect internal reference if it's accidentally switched on?
P.S. Sorry about my funny english.
Yes, you are correct that there will be a voltage drop. That would be a trade off if you would want to put a resistor on the VREF pin of the part. If the internal reference is enabled, the VREF pin will act as an output pin and the output impedance seen on this pin is less than 1 ohm. If the internal reference is disabled, the VREF pin will act as an input pin and the input impedance, as you have said will be 12k to 24k ohms.
Would you be pushing thru with the jumpers and links on your boards?
Are the two devices connected electrically? If so, could you share a schematic diagram? The schematics will be able to tell us how we can protect the pins and in effect, the devices.
Generally, there should be no problem with the VREF pin being connected to VDD pin. The reference is powered down by default and is enabled by setting Bit D9 in the power-down/reference control register to 1.
So as long as you don't "accidentally" enable the reference, there should be no problem.
Hi msamera and thanks for your reply.
The project are two with only one chip on it.
One work with 5V and one with 3V3.
It's a very simple board with stabilized power supply section (LDO) and the AD5593.
It's simple experiment board for my students.
They can program it and learn about ADC and DAC.
So they can use external or internal VREF and there is the risk to accidentally swich on internal reference with VDD on it.
I think to put a 1K resistor to limit the current (5ma) but it change the reading.
It would be nice if I could have a behaviour like:
1)VDD if nothing connected to REF and internal switched off
2)internal reference, if switched on and irrespective of the status of REF
3)An external reference if it connected to REF and the internal is switched off
Is there a circuitry to do that?
Thanks and regards.
If you are planning on putting a resistor across VDD and REF, make sure that the LDO will be able to provide enough current to the part while burning a couple of milliamps on the resistor.
You referred to a change in reading. Could you specify which reading are you referring to?
You may want to check the evaluation board of the AD5593. We use physical links/jumpers similarly to what you are trying to achieve. You may refer to UG-756 for details on how the board can be used.
If you have any further questions, please do not hesitate to ask.
thanks for reply and thanks to your patience ;-)
If I understand the datasheet... VREF has an Input Impedance of 12K or 24K ... if I put a 1K resistor across VDD and VREF i have a voltage drop of about a 1/13*VDD (or 1/25*VDD). Is it correct?
I use a LDO capable of 1A ;-)
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