DAC161S997: DAC Output Problem

user4872449

Part Number: DAC161S997

Hi,

I have msp-exp432p4111 and DAC161s997 and using the firmware of TIDA-00648

        Setup_DAC161  (DAC161_STD_ERR_CONFIG_MASKED, 0, 21800);
        DAC161_Set_Out_Value(x* 2730);

x is the mA value which i want to get but lets say x =5 , then output is become something like 2.5mA. if i use 5400 instead of 2730 then output is normal until 8mA after that output changes slower like if x=15 then output is 9mA.

void USCIB0_setupMasterSPI(void)
{

	DAC_USCIB0_PORTDIR |= (USCIB0_SIMO + USCIB0_SOMI+ USCIB0_CLK);
	DAC_USCIB0_PORTSEL |= (USCIB0_SIMO + USCIB0_SOMI+ USCIB0_CLK);             // Assign SPI pins to Primary Peripheral of USCI_B0
	DAC_CS_PORTOUT |= DAC_CS_N;
	DAC_CS_PORTDIR |= DAC_CS_N;

	EUSCI_B0->CTLW0 |= EUSCI_B_CTLW0_SWRST;                                                       // Enable SW reset
	EUSCI_B0->CTLW0 |= (EUSCI_B_CTLW0_SWRST + EUSCI_B_CTLW0_MST + EUSCI_B_CTLW0_MSB + EUSCI_B_CTLW0_SYNC + EUSCI_B_CTLW0_CKPH );     // SPI Master, 3 wire, synchronous mode
        EUSCI_B0->CTLW0 |= EUSCI_B_CTLW0_SSEL__SMCLK; // SMCLK
        EUSCI_B0->BRW = 8;
	EUSCI_B0->CTLW0 &= ~EUSCI_B_CTLW0_SWRST;                                              // Clear SW reset, resume operation
}

void Setup_DAC161 (unsigned short errConfig, unsigned short errLow_uA, unsigned short errHigh_uA)
{
	unsigned short errValue;

	DAC161_Write_Regs (&errConfig, DAC161_ERR_CONFIG_REG, 2);

	errValue = DAC161_CONVERT_ERR_VALUE(errLow_uA) & 0x7f00;
	DAC161_Write_Regs (&errValue, DAC161_ERR_LOW_REG, 2);

	errValue = DAC161_CONVERT_ERR_VALUE(errHigh_uA) & 0xff00;
	if (errValue < 0x80)
		errValue = 0x80;
	DAC161_Write_Regs (&errValue, DAC161_ERR_HIGH_REG, 2);

}

over 5 years ago

0 Garrett Satterfield over 5 years ago

TI__Expert 5820 points

Hello,

What hardware are you using to test DAC161S997? Can you provide a schematic?

The loop current should be (DACCODE/65536)*24mA if the DACCODE register is being written properly and the hardware is setup correctly. Can you use the DAC161_Read_Status function to see if there are alarm conditions at each DAC code you set? You can also use the DAC161_Read_Regs to read the DAC code register and ensure it is being programmed to the value intended.

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

I started to think my problem is the transistor. I used www.digikey.com/.../2094410 . What do you think about this ?

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

Hello,

Using that transistor should be fine. The parameters of the transistor are not crucial since it is in the feedback loop of the internal amplifier. How are you connecting your load and power supply? I see you have 24V connected to loop+. Are you connecting your load across J1 directly? This configuration will not work. The power supply and load resistor must be in series with the transmitter.

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

Normally 24V will be connected to a dc/dc converter so i can use it but for now i was just using exp-msp432p4111 board which gets power from usb and an other PCB for DAC which i shared its schematic gets 3.3V from MSP board. Also loop+ gets 24V from an other power supply. I've linked GNDs together. So i couldnt get what you mean. What will not work and what do you mean by be in series with the transmitter. Thank you for your replies.

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

The loop power supply ground should be referenced between collector of the NPN and the OUT pin of the DAC161S997. I am not sure why you have the 24V connection at the collector of the NPN past the input protection diode. Is this 24V referenced to COM on DAC161S997? The loop power supply should be connected across the terminals of J1 so it and the load are in a series loop with the transmitter.

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

As you can see there is a LDO connected to loop+. It is the same with mine! I am getting 24v from there. It is not an other 24v supply. So i can convert the 24V which comes from J1, to 3.3V so i can feed my MCU and etc. Thank you.

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

Hello,

Okay, understood about the 24V loop supply. Do you have a schematic of your hardware that you could provide?

Have you tried reading back the DAC data register as well as the alarm register as I suggested previously? This will ensure that the correct data is is being written and ensure that there are no alarm conditions occurring.

Thanks,
Garrett

0 Garrett Satterfield over 5 years ago in reply to Garrett Satterfield

TI__Expert 5820 points

Hi,

Any update on this thread?

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

I was connecting the output to 100R resistor through GND and sensing the voltage from that resistor. but when i cancel the resistor and connecting the output direcly multimeter the value of output is works fine. What might cause that ? Also i have a zener diode after 100R resistor.

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

Hello,

I am not sure how the image you provided fits into the schematic you posted earlier. Can you show how you are connecting this load to the schematic above? When you are connecting the multimeter are you measuring the voltage across the load or current through the meter?

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

Hmm think the last schematic is an other board and i am connecting 24v supply's power to my DAC board, 24V supply's ground to the last board as ground. Then loop- pin which in DAC board connected to last schematic. When i use multimeter i am sensing current, not voltage.

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

Hello,

Is the GND of the supply shorted to Loop- as you have drawn? Have you tried connecting a single load resistor between the supply GND and Loop-? What is the purpose of the zener diode?

Thanks,
Garrett

0 Garrett Satterfield over 5 years ago in reply to Garrett Satterfield

TI__Expert 5820 points

Hello,

Any update on this thread?

Thanks,
Garrett

0 user4872449 over 5 years ago in reply to Garrett Satterfield

Intellectual 760 points

Zener is needed because as over voltage protection.

0 Garrett Satterfield over 5 years ago in reply to user4872449

TI__Expert 5820 points

Hello,

The zener diode in the schematic is very low voltage and will result in some of the loop current flowing through it instead of all current flowing through the load resistor. I still don't think I understand your loop setup based on the previous drawing. It looks like loop GND and loop- are shorted together. Is the GND symbol referenced to the loop GND?

Thanks,
Garrett

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DAC161S997: DAC Output Problem