DAC8811: The output data is incorrect

Hi,

We are reviewing this and will get back to you shortly.

Thanks,
Lucas

We connected pin 4 of U1 (OP2838) to -5V (- VP).
The code is

for(i=0;i<36;i++)
{

// dD = -0.5;
dD = sin(i*2*3.1415927/36);
if(dD>=0)
{
usDat = dD*32767 ;
}
else
{
uiD = 65536;
uiD = uiD + dD*32768;
usDat = uiD;
}
// usDat = (dD+1.0)*65535/2 ;
// usDat = 0xfff;

// usDat = i ;
// usDat = 32768 + usDat*910;
DA_Set_Fun(usDat);
Delay_2us(10);
}

The output signal is:（the yellow is TP8 。 the blie is TP7）

Hi,

Are you observing this issue on multiple boards or just one?

Can you verify that VDD and VREF are stable during this time?

Thanks,
Lucas

the  vcc  is 3.3v  .    vp is  +5v

I have confirmed that the vcc and +5v voltage is stable

I will be testing multiple boards these days

I have tested multiple boards and the results are the same

Hi,

I'm not seeing any immediate issues with the schematic.

Are you able to measure or plot the SPI write to the device?

Thanks,
Lucas

Thks for your reply.  Above is the SDI CLK CS pin

Here is the code

/***************************************************************************************
* @ʵÏÖЧ¹û ÉèÖø÷¸öIO¿ÚµÄ¹¤×÷״̬
***************************************************************************************/
void DA_Set_Fun(unsigned short int usDat)
{
unsigned char i;
unsigned short int usD;

IO_CS_HIGH;
IO_CLK_HIGH;
IO_DI_LOW;

Delay_ms(1);

usD = usDat;

IO_CS_LOW;

for(i=0;i<16;i++)
{

IO_CLK_LOW;
if((usD&0x8000)==0)
{
IO_DI_LOW;
}
else
{
IO_DI_HIGH;
}
Delay_2us(5);
IO_CLK_HIGH;
Delay_2us(4);
usD = usD<<1;

}
IO_CLK_LOW;
Delay_2us(6);
IO_CLK_HIGH;

// Delay_2us(1);
IO_CS_HIGH;

}

Hi,

The SPI looks alright too. Let me verify a few things and get back to you.

Thanks,
Lucas

I adjusted the timing and felt that the waveform was a bit normal, but the output signal still seems to be incorrect

the yellow is TP7, the blue is TP8

Hello,

Thanks for the additional waveform. Lucas is looking into some more ideas and will get back to you shortly. 

Best,

Katlyne Jones

Seems like you have fixed the digital issue, but you have the output buffer clipping against the supply.  You should confirm by simulation if you have a linear output range with your given supplies.  Is it possible to increase the supply values?

When I remove R5 and R6, the waveform of TP7 and TP8 looks like this

Whether the VP and 4-pin of  U1 is+15V, -15V,+5V, or -5V, the result is the same

When I remove U1 and connect resistor R to ground on pin 5 of U2, the output waveform is

But no matter how I change the R value, the amplitude of the output waveform remains unchanged, only the bias value changes

Thank you very much for your answer, but in my previous experiment, the 4 pins of U1 were connected to negative pressure through jumper wires

I have replaced the amplifier with a new one（TPA2681）, and  The output waveform of TP8 is

the power of TPA2681 is  +15V -15V.

What I don't understand is that my reference voltage is+5V(Vref), shouldn't the output signal be 0-5V? Why is the voltage amplitude more than three times larger

Hi,

The IOUT of the DAC8811 cannot go past -VREF. I would verify that you are measuring in respect to GND (and that you are measuring TP8, the test point connected to the IOUT of the DAC) and that the probe you are using is x10.

Can you provide an updated schematic detailing what components are populated in your circuit?

Thanks,
Lucas

I'm sorry, that signal is TP7

I didn't modify any circuit diagrams, I just replaced the  amplifier with TPA2681

Hi,

Can you describe how you replaced the amplifier?
The OPA2828 is a 8 pin HVSSOP, and the TPA2681 is a 5 pin SOT23.

Are you just using wires to connect the pins?

Please make sure:
DAC IOUT is connected to TPA pin 4 (-In)
GND is connected to TPA pin 3 (+In)
VP is connected to TPA pin 5 (+Vs)
Your negative supply is connected to TPA pin 2 (-Vs)
The TPA pin 1 (Out) is connected to TP7 and DAC RFB.

Thanks,
Lucas

The package of TPA2681 includes SOP-8

I tested it through jumper wires

What I don't understand is that my reference voltage is+5V(Vref), shouldn't the output signal be 0-5V? Why is the voltage amplitude more than three times larger

I have identified the issue, it is my Vref voltage that is incorrect

Hi,

Is everything working correctly now? Is the output of the amplifier as intended?

Thanks,
Lucas

YES,Yes, everything is OK. Thank you very much for your help