DAC8760: Design of DAC8760

Hi Gokul,

It is fine to connect AVSS and the thermal pad to ground if you are not using the device in bipolar mode. The I-FLT indicates either that the circuit is open or the compliance voltage maximum has been exceeded. The output stage transistor requires some voltage headroom to remain in the correct operating region. The alarm condition in this case occurs when the voltage at IOUT exceeds AVDD - 2V. The voltage required to drive the load will depend on the load resistance and maximum current. With a 12V supply the maximum voltage at IOUT will be 10V (before alarm condition) which can drive a maximum load of 500 ohms at 20mA. The alarm will occur if IOUT exceeds about 10V.

Adding more resistance like a 1kOhm load will cause an alarm condition without increasing AVDD. What current value do you measure in the loop with the multimeter? A 250ohm load in series with the multimeter should not cause a compliance voltage alarm condition.

Thanks,

Garrett

6708.SCHEMATIC1 - ANALOG OUTPUT CARD.pdf

Hi Gokul,

I looked over your schematic and didn't see anything that would necessarily cause a problem. I notice that you are using the external transistor with the BOOST pin but you did not include the emitter resistance or capacitor as shown in Fig. 87. I would recommend following the application diagrams included in the datasheet. I also noticed that you are using a very large capacitor of 1uF between CMP and VOUT. Is this the intended value? This will increase settling time and reduce the bandwidth. The data sheet shows a compensation capacitor on the order of 1nF typically.

To solve the alarm problem I would recommend disconnecting the external transistor and connecting only a 250ohm resistor from IOUT to GND. Too much resistance between IOUT and GND could cause the compliance headroom alarm. If you use only a 250ohm resistor in series with  a current meter what current do you measure in the loop? Does the alarm still trigger?

Thanks,

Garrett

Hi Garrett Satterfield,

I remove external transistor and place 250E from IOUT to GND, but no more current on meter.

After I check my PCB, i find out boost and AVDD are short. I completely check out PCB tracks, no short on PCB. There's any possibility to short on internal circuit.

In AVDD pin measure 4V, without  any exteranl supply for AVDD.

Anything need to check on software at register level , to solve BOOST and AVDD short.  

Please help  me to solve the problem.

Hi Gokul,

Were you able to measure current through the load before removing the external transistor?

It appears that there is an issue with your schematic. The net you call VADD which is the input to your +/-15V regulator (pin 2) is connected directly to DVDD of the DAC8760. I assume the voltage of AVDD is around 24V. Can you confirm if this is how it is physically connected? This will cause device damage as the absolute maximum voltage between DVDD and GND is 6V. 

If this is a lower voltage intended to power DVDD, then DVDD-EN should be tied to ground so that DVDD is externally supplied.

Thanks,
Garrett

Hi Garrett Satterfield,

I my measure current through meter in two points, 

1. In schematic I place 1k and 15E on IOUT pin to GND. I remove 1k and then measure current directly from IOUT pin.

2. After that I place 0E and 15E on IOUT pin to GND, then connect 250E to IOUT connector to GND. 

DVDD-EN -- NC

DVDD -- External 5V

AVDD and AVSS -- External +/-15V

Please Help me to come out from this problem. Already, I Completed VOUT part, IOUT part only remaining.

Please give me some notes to follow on Hardware and Software to check and complete work

Hi Garrett Satterfield,

Sorry for Replay. I Planned to work with DAC8670 in QFN package. I attached Schematic for QFN package as followed in Development Board. 

Please Check the Schematic to get IOUT output.

From last Baord, 

DVDD-EN not connect to ground, its open. DAC.pdfDAC8760Module.pdf

I connect 15Kohm resistor across ISET-R pin with respect to ground. When I measure Voltage at ISET-R pin is 4V. But No Voltage at IOUT PIn. 

#include "project.h"

#include "DAC8760.h"

#include "MAX7219BB.h"

#include "stdio.h"

 

 

 

static int reg_dat;

static int control_reg,config_reg,gain_reg,offset_reg;

 

 

int main(void)

{

    int alarm_status=0;

    uint8 checkbit;

    char str[24];

   

    control_reg=RANGE_0to10V | EXT_RES_Enable | OUTPUT_Enable;

    config_reg=Alternate_Power_Down | DUALOUTPUT_Enable | IOUT_RANGE_DUAL_Enable_0to20mA ;

    gain_reg=0;

   

    

    CyGlobalIntEnable;

   

    SPI_DAC8760_Initialise(control_reg,config_reg,gain_reg,offset_reg);   

    SPI_DAC8760_Write_Data_Register(0);   

    

    CyDelay(1000);

   

    UART_1_Start();

   

    for(;;)

    {

       

//        alarm_status=SPI_DAC8760_Read_Address(READ_CONTROL);

//        CyDelay(1000);

//       

        SPI_DAC8760_Write_Data_Register(0);

        CyDelayUs(200);

        alarm_status=SPI_DAC8760_Read_Address(READ_STATUS);

        switch(alarm_status)

        {

            case 1:

                UART_1_UartPutString("\r\nTemperature is high...\r\n");

                break;

            case 2:

                UART_1_UartPutString("\r\nSlew Rate Error...\r\n");

                break;

            case 4:

                UART_1_UartPutString("\r\nIOUT or Compliance Volt Violate...\r\n");

                break;

            case 8:

                UART_1_UartPutString("\r\nWatch Dog Timer Error...\r\n");

                break;

            case 16:

                UART_1_UartPutString("\r\nCRC Error...\r\n");

                break;

            default:

                UART_1_UartPutString("\r\nNo Error.....\r\n");

        }

        CyDelay(3000);

       

        

        

        SPI_DAC8760_Write_Data_Register(16383); /// DAC Data Register

        CyDelayUs(200);

        alarm_status=SPI_DAC8760_Read_Address(READ_STATUS);

        switch(alarm_status)

        {

            case 1:

                UART_1_UartPutString("\r\nTemperature is high...\r\n");

                break;

            case 2:

                UART_1_UartPutString("\r\nSlew Rate Error...\r\n");

                break;

            case 4:

                UART_1_UartPutString("\r\nIOUT or Compliance Volt Violate...\r\n");

                break;

            case 8:

                UART_1_UartPutString("\r\nWatch Dog Timer Error...\r\n");

                break;

            case 16:

                UART_1_UartPutString("\r\nCRC Error...\r\n");

                break;

            default:

                UART_1_UartPutString("\r\nNo Error.....\r\n");

        }

        UART_1_UartPutString("\r\n");

        CyDelay(3000);

       

        SPI_DAC8760_Write_Data_Register(32767);/// DAC Data Register

        CyDelayUs(200);

        alarm_status=SPI_DAC8760_Read_Address(READ_STATUS);

        switch(alarm_status)

        {

            case 1:

                UART_1_UartPutString("\r\nTemperature is high...\r\n");

                break;

            case 2:

                UART_1_UartPutString("\r\nSlew Rate Error...\r\n");

                break;

            case 4:

                UART_1_UartPutString("\r\nIOUT or Compliance Volt Violate...\r\n");

                break;

            case 8:

                UART_1_UartPutString("\r\nWatch Dog Timer Error...\r\n");

                break;

            case 16:

                UART_1_UartPutString("\r\nCRC Error...\r\n");

                break;

            default:

                UART_1_UartPutString("\r\nNo Error.....\r\n");

        }

        UART_1_UartPutString("\r\n");

        CyDelay(3000);

       

        SPI_DAC8760_Write_Data_Register(49150); /// DAC Data Register

        CyDelayUs(200);

        alarm_status=SPI_DAC8760_Read_Address(READ_STATUS);

        switch(alarm_status)

        {

            case 1:

                UART_1_UartPutString("\r\nTemperature is high...\r\n");

                break;

            case 2:

                UART_1_UartPutString("\r\nSlew Rate Error...\r\n");

                break;

            case 4:

                UART_1_UartPutString("\r\nIOUT or Compliance Volt Violate...\r\n");

                break;

            case 8:

                UART_1_UartPutString("\r\nWatch Dog Timer Error...\r\n");

                break;

            case 16:

                UART_1_UartPutString("\r\nCRC Error...\r\n");

                break;

            default:

                UART_1_UartPutString("\r\nNo Error.....\r\n");

        }

        UART_1_UartPutString("\r\n");

        CyDelay(3000);

 

       

        SPI_DAC8760_Write_Data_Register(65535); /// DAC Data Register

        CyDelayUs(200);

        alarm_status=SPI_DAC8760_Read_Address(READ_STATUS);

        switch(alarm_status)

        {

            case 1:

                UART_1_UartPutString("\r\nTemperature is high...\r\n");

                break;

            case 2:

                UART_1_UartPutString("\r\nSlew Rate Error...\r\n");

                break;

            case 4:

                UART_1_UartPutString("\r\nIOUT or Compliance Volt Violate...\r\n");

                break;

            case 8:

                UART_1_UartPutString("\r\nWatch Dog Timer Error...\r\n");

                break;

            case 16:

                UART_1_UartPutString("\r\nCRC Error...\r\n");

                break;

            default:

                UART_1_UartPutString("\r\nNo Error.....\r\n");

        }

        UART_1_UartPutString("\r\n");

        CyDelay(3000);

       

    }

}

 

 

Sorry Sir for late reply, i busy with other issuses, my software Eng not here to reply to you.

My IOUT issue still hold on.

I m not using external transistor across boost pin. I Using External ISET-R Resistor (15K) and then i measure 4V across ISET-R Pin, but no voltage drop on IOUT pin even open or closed Circuit.

You ask me to Check SPI functionality, So that i attached my Code ( we using cypress micro-controller).

Please Help me, My Whole product is hold on because of IOUT issue.

Hi Gokul,

I reviewed your attached code but of course I do not know how your functions are implemented and if they correctly write to the device. Since you have gotten the voltage output to work I assume your SPI interface is correct.

Can you read back the configuration register and ensure that DB10:DB9 are set correctly to enable the current output?

Are you still seeing the IOUT fault alarm?

If you measure 4V at Rset then it seems like the DAC is set correctly and you should see 15V on Iout open circuit. If Iout is disabled then you shouldn't see 4V at Rset. Is it possible that there is a connection problem between the device pin and where you are measuring?

Have you tested across multiple boards?

Thanks,

Garrett

Hi Garett,

         I have an update while working with one board I am getting an error message of High Temperature and while using with the other board I am getting no error but even the Voltage on the Current Output Pin remains low i.e. 0V. I need to know whether the Loop Voltage Has to be given externally or it will be internally generated. In One Board there is short between Avddd and Boost Pin will this affect the IC I need to know How it will affect ?

Thanks.

Regards,

Gokul

Hi Garrett,

I test across BOOST and AVDD Pin, it shows 40 Ohm resistance with some continuity (In my working board (HTSOP Package) . But i measure in separate QFN

Package across BOOST and AVDD Pin,  it shows 40 Ohm resistance without continuity.

In my working board, due to short of BOOST and AVDD Pin, its may affect the internal OP-AMP and MOSFET operation  (fig. 93 datasheet) . 

Hi Garrett,

Yes Voltage Output work properly, upto +10V. We not work on -10V because of PCB design problem.

No voltage on IOUT Pin, but some voltage drop across (15K) on ISET pin (4V).

So, We plan to develop other sample PCB for DAC using QFN package.

I ll send schematic for QFN package, please verify it. Help Us.