• State TI Thinks Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 288 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC8551: DAC8551 incorrect Vout

Andrew Xiang
Prodigy 130 points
Part Number: DAC8551
Other Parts Discussed in Thread: DAC63001, , DAC80501, DAC8881

We have issues with DAC8551IDGKR on some boards. The Vout does not match with the input. 

The chip does not have reset. We are using GPIO to simulate the SPI signal. Most of the boards work okay. Few gave me intermittent issues. If I power cycle, it might work again. 

Sometime we replace the chip and it works. 

I notice the chip does not have RESET, GPIO power up may have random signal to its SPI pins. Not sure if that is the reason. 

inline void write_dac(unsigned short dac_value)

{

uint32_t dummy;

uint32_t value1;

uint32_t temp;

value1 = dac_value;

temp=0x800000;

AT91F_PIO_SetOutput(PORT_DAC, DAC_CLK);

for (dummy = 0; dummy < 24; dummy++)

{

if (temp & value1)

AT91F_PIO_SetOutput(PORT_DAC, DAC_DIN);

else

AT91F_PIO_ClearOutput(PORT_DAC, DAC_DIN);

AT91F_PIO_ClearOutput(PORT_DAC, DAC_CLK);

temp=temp>>1;

AT91F_PIO_SetOutput(PORT_DAC, DAC_CLK);

}

}

  • 0
    TI__Mastermind 31488 points

    Hi Andrew,

    Can you share a schematic? Do the boards with the issue ever work on powerup and then stop working? Or do they always have the issue right after powerup?

    What incorrect VOUT are you seeing? Does it remain at 0V? Or some other voltage? Does VOUT change when you write new data? Or is it fixed?

    Can you measure the GPIOs and VDD at startup for a non-working device and share a screenshot? You can also share the sequence of a working device and we can compare. 

    Please also share a screenshot of a write sequence on a non-working and working device. Maybe the timing is slightly off and causing the DAC to interpret the data differently.

    Best,

    Katlynne 

  • 0 in reply to Katlynne Jones
    Prodigy 130 points

    It does not happen often, Rare but detrimental. So I cannot make measurement. 

    I modified my schematics and setup GPIOs first before supply the 5V. But I hope the chip has a reset function. I suspect it is from startup with GPIOs at random at power up. 

    Can I send a code through SPI so the chip RESET itself?

  • 0 in reply to Andrew Xiang
    TI__Guru 53333 points

    We are reviewing now.  The US holiday weekend will delay the response.

  • 0 in reply to Andrew Xiang
    TI__Mastermind 31488 points

    Hi Andrew, 

    There is not a software reset of this device. 

    Can you answer a few of my previous questions? 

    Can you share a schematic? Do the boards with the issue ever work on powerup and then stop working? Or do they always have the issue right after powerup?

    What incorrect VOUT are you seeing? Does it remain at 0V? Or some other voltage? Does VOUT change when you write new data? Or is it fixed?

    New question, the GPIOs that are connected to the SPI pins are turned on before the DAC VDD supply is turned on? 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 130 points

    VOUT  not 0. I have to power cycle to fix the problem. I think the chip got into some bad state. Missing a bit I think. 

    I do have to initialize the GPIOs before power on the DAC. I think that solved the problem. 

    I think it would be nice to have a reset when I have no control of power. 

  • 0 in reply to Andrew Xiang
    TI__Mastermind 31488 points

    Hi Andrew,

    Understood. Many of our devices do have a SW reset feature. I am not sure why this one does not (it's a pretty old part). 

    If you have additional questions, please let me know. Otherwise we will close this thread for now. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 130 points

    do you have newer replacement part that we can switch to?

    Please recommend. 

  • 0 in reply to Andrew Xiang
    TI__Mastermind 31488 points

    Hi Andrew, 

    The DAC80501 is a newer device that we recommend to replace the DAC8551, and it has a SW reset. It does not have the same pinout so you would have to update that. It also does not expose the VFB pin of the output buffer. If that is a requirement, you could consider the DAC63001. The DAC63001 also has a GPI pin that can be configured as a hardware reset (there is also a SW reset). 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Prodigy 130 points

    do you have a 16bit dac with a RESET pin? Sometime the SPI/I2C is in some funny state and you cannot write the software RESET in. If not, I'd rather use a LDO to do the reset by power cycle. 

  • 0 in reply to Andrew Xiang
    TI__Mastermind 31488 points

    Hi Andrew, 

    It looks like the DAC8881 has a reset pin. 

    Best,

    Katlynne Jones