DAC8562T: VREFOUT voltage dropping

Hi,

From your schematics, I am assuming you have 200nF cap on RefOut pin which is OK.

Whats the power up sequence?

Can you please tell me whats the voltage on RefOut pin after power up before sending any command to DAC?

Can you do the following for me to get a better understanding.

Make sure CLR is tied to high

1. Power up Device

2. Send RESET command

 (cmd:101, Add:000, Data:0000_0001)

3. Wait for 5-10ms

4. Enable Internal Reference of DAC

(cmd:111, Add:000, Data:0000_0001)

5. Measure Vref

If Vref reads 2.5V, then issue another command to update DAC Voltage and set DAC Gain 1

(cmd:000, Add:010, Data:0000_0011)

6. Send code to update DAC voltage (Any value is fine)

Regards,

AK

Thank you for your answer,

This shot give the power up sequence. Supply is a bit slow but when I use it on eval board, it's ok.

Yellow: 3.3V supply

Blue: nCLR  (nLDAC drived in the same way)

Purple: Vrefout. 0V on startup, rise to 2.5V after commands

Green: nSYNC

Commands sequences (I was already doing something near that you suggested):

 /* POR */
  0x28,0x00,0x01

  msleep(10);

  /* LDAC inactive */
  0x30, 0x00, 0x03,

  /* Internal ref */
  0xFF, 0xFF, 0xFF,

  /* Gain = 1 */
  0x02, 0x00, 0x03,

I'm using a bitbang spi interface for configuration, and once done, I use I2S bus of my CPU. It send continuous clock on SCLK pin, with data and SYNC.
(2 chan at 96kHz).

I write first chan, then 2nd + DAC update (as you can see on previous post).

It seems working when I write low speed values, but not with my I2S. I don't think that it is communication problems because it's working on eval board. Maybe with higher rate, it consume more power, and reveal some hardware problem ?

Hi,

Interface supports upto 50MHz So I dont think this has anything to do with higher rate. whats the update rate you are using, SCLK Frequency?

Could you please check one more thing, when reference is drooping whats the voltage and current levels on supply pin?

Regards,

AK

Hello,

96kHz output sampling rate, on 2 channels. So 192kHz data input rate. SCLK is around 5 MHz.

I just measured DAC current, with a 10 ohm resistor  between supply and dac8562T (R65 on previous schematic).

In blue , voltage around resistor (10ohm, so 72mV peak correspond to 7.2mA, a bit high according to the datasheet).

In purple, it's the VRFOUT. (/!\ measure compared to Vsupply, and not GND because I needed to isolate my oscilloscope from GND to measure between my resistor).

So we can read 0V, which mean that VRFOUT= 3.3V, and when it drop, current rise.

Than you for your answer,

Romain

Hi Romain,

Thanks for providing us with the details. 7.2mA current for this device seems to be on the higher side. Having said that when you tried with eval board, Did you use the same bit bang SPI interface or used the EVAL software to do the test?

I am assuming your DAC output is isolated for this test. Can you please check with normal SPI interface other than bit bang scheme to isolate interface is not the issue?

Regards,

AK

I didn't use eval software. I use I²S (Inter-IC Sound) bus with eval board, and everything is ok.( SPI bitbang is just for configuration).

And with my board, I can plug, in parallel, the eval board. So physically the SAME bus for talking to DACs is used for eval board and for my DAC8562

Outputs are left unconnected.

"Can you please check with normal SPI interface other than bit bang scheme to isolate interface is not the issue?"

I did not really understand your question. Do you want me to use another bus to communicate with the device ?
(My bus currently works well with eval board).

Hi,

One quick check, did you happen to check with external reference as well? That will give us some clue regarding internal reference misbehavior.

Regards,

AK

Hi,

Did you have look at the above suggestions?  Also I want you to check with different capacitor value on Ref Pin, Can you try with 1uF Capacitor?

Regards,

AK

Hi

Glad that your problem got solved. Please test system thoroughly and let me know any additional support you need on the same.

I will close the thread now, should you have any questions in future, you can reopen the same.

Regards,

AK