not operate DAC8760

Kang,

You clock phase and polarity settings are correct. The protocol you are implementing to communicate with the device also looks correct, both in code and in the oscilloscope captures you have provided. There is considerable ringing and cross-talk in your SPI signals but I do not think that is the cause of this issue.

It would be helpful if you could provide a schematic to double check your hardware rather than words describing the connections in the design.

In the oscilloscope capture you provided you are writing address byte 0x01 with data 0xFFFF, which corresponds to writing full-scale data to the DAC Data register. Is this the complete write sequence that you are using to test communication with the device?

schematic include

 you say I am writing adreess  byte 0x01 with data 0xFFFF

becasue TMS230F28335 has SPI with sending 16bit

but DAC8760 has 24bit adresss

so I am sending each 8bit

and I checked sending correct data by osciloscope

and is it right including schematic??

Kang,

Thanks for following up. More comments for you:

kang jeonmook said:

 you say I am writing adreess  byte 0x01 with data 0xFFFF

becasue TMS230F28335 has SPI with sending 16bit

but DAC8760 has 24bit adresss

so I am sending each 8bi

Understood - we discussed the format you are using to communicate with the device in a previous E2E thread. The method you are using to communicate with the device looks good in both code and in the oscilloscope captures that you provided.

The oscilloscope capture you provided writes the 24-bit word 0x01FFFF which writes full-scale to the DAC Data Register. If this is the only write that you perform I would not expect for the device to respond in any way because neither the voltage or current outputs are enabled. In order to enable the analog outputs you need to write a '1' to bit 12 in the Control Register (address 0x55). With the outputs active you should see the voltage or current output respond to data placed in the DAC Data Register. The output mode that is active is set by the RANGE bits in the Control Register.

kang jeonmook said:

and is it right including schematic??

Functionally the schematic looks okay. There are several off-page connectors that make some details difficult to access. I would suggest that decoupling capacitors are included on AVDD and DVDD. A small decoupling cap should also be included on the REFIN to REFOUT connection.

I am solved.

problem didnt connect analoge and digital with seperated

but problem appear.too

as you see, even though I am setting 0~5V range in control register

but this picture show Vout is 300mV~7V

so I did set gain register and zero register..

but DAC8760 is still showing 300mV~7V

Kang,

Is the oscilloscope ground connected to the board ground?

Can you measure the reference voltage?

i am using a internal reference

Kang,

You can measure the internal reference at the REFOUT pin.

it is 2.76V

Kang,

You have verified that your system and measurement equipment are grounded correctly?

when I sended 0xffff to data register, REFout is 5V

when I sended 0x0000 to data register, REFout is 0V 

Kang,

Writing to the DAC Data Register should not have any impact on the output of the reference voltage. Do you have an evaluation module for the DAC8760? If so I would suggest that you verify your SPI communication using the known-working EVM. Then we can move on to debugging the analog issues on your PCB that are leading to accuracy issues on the outputs.

I am mistaken to measure REFout

REFout is always 5V

 and when I am sending 0x0000 to 0xffff, I am looked to jumping 3.3V to 7V immediately

cf) AVDD is 7V, not 5V

Kang,

Can you provide a full-schematic of the board you are using to make these measurements? If you could share the layout as well that would be helpful. I'd like to also know exactly where you are making the measurement as well (Where is the oscilloscope lead placed? Where is the ground lead of the oscilloscope placed?).

when I measered  Vout,  I placed on VSGND of motordriver

below address appeares motordriver spec

http://www.motorplus.kr/shop/goods/goods_view.php?&goodsno=597&category=003002

answer please.

Kang,

Have you made any measurements with the DAC unloaded?

Yes, but the result is identical

and sounds weird, if AVDD is 12V and I send 0x01ffff, Vout is 12V

                                   if AVDD is 5V and I send 0x01ffff, Vout is 5V

I don`t know what problem is

cf)REFOUT is 5V

Kang,

Do you have any way of sharing the layout of this design?

What is the output voltage at zero-scale for each of those cases? What about mid-scale?

The only way the output voltage should be tracking with the supply voltage is if the output amplifiers are operating open loop and simply hitting their rails. If this is the case we should see the full-scale output regardless of what the input code is.

I don`t know what means zero-scale??

zero scale is 0V, isn`t it??

Kang,

Zero-scale means the DAC data register contains 0x0000. Mid-scale is 0x8000. Full-scale is 0xFFFF. Please let me know what the output voltage is for each DAC data word.

As I have mentioned, providing the layout would be helpful as well.

layout means circuit diagram?

Kang,

Layout means the GERBER files or project files used to create the printed circuit board (PCB). 

if I send 0x8888, Vout is 2.5V

if I send 0x0000, Vout is 0V

but if I send 0xffff, Vout is 7V

1537.Schematic1.sch

measurement video

increase sending value until 0xffff

i`m waiting you

Kang,

kang jeonmook said:

if I send 0x8888, Vout is 2.5V

if I send 0x0000, Vout is 0V

but if I send 0xffff, Vout is 7V

What is AVDD in this case? 7V? Previously you mentioned if AVDD is 5V then full-scale data output is 5V. Similarly if AVDD was 12V full-scale data output is 12V.

What is the thermal pad connected to?

The PCB layout would still be helpful. The schematic you shared is not the layout.

AVDD is 7V

thermal pad was connected to  AVSS(GND)

PCB layout is nothing 

because I am soldering the circuit board directly

help me...ㅠㅠ

Kang,

I see several independent ground connections in your schematic, are all of these grounds connected to one another eventually? All of the grounds need to be connected to one another or you have several floating potentials in this design that is going to cause either parametric degradation, complete lack of functionality, or conceivably permanent damage to the components.

If you do not have a layout then the schematic you have shared is relatively meaningless. There could be any number of issues in the connections that you have made manually that is leading to a considerable gain error on the voltage output.