AD7839 DAC

DGND should be 0V not -5V. This may have damaged the AD7839 as it breaks the absolute maximum ratings.

Are you using the EVAL-AD7839EBZ evaluation board to test the AD7839. If you are you will be using the 3 74HCT573 latches to connect the data to the DAC.

You will need to get your TI micro to put values for the address bits and data bits on the bus and then pulse the LATCH pins (pin 11) of each of the latches. This will copy the data from the 36 way connector side to the DAC.

When you have transferred all the data to the DAC pins you can pulse CS low to update the DAC register. You will need to pulse LDAC low to get the output updated or you can tie it low.

CLR should be high to keep the AD7839 in normal mode.

I am using a voltage regulator to convert 15 v to 5v. the main power supply has a negative port, gnd port and a positive port. I have connected the positive port to the input of the voltage regulator and am taking the negative of the main power supply as DGND. Is it wrong?

Yes I am using EVAL-AD7839EBZ evaluation board to test the AD7839. I am confused with the things that I need to connect in order to operate the DAC. I have attached all the links properly. when I connect the output of the TI controller to the evaluation board the voltage drops to 0.7 volts. Do I need to connect the WR, CS, and the LDAC signals?. And where do I need to connect the ground of the TI controller output signal. Previously I had connected it to pin no 22 of the evaluation board.

is it mandatory to use Clr and Ldac. To run the evaluation board?

I am using a voltage regulator to convert 15 v to 5v. the main power supply has a negative port, gnd port and a positive port. I have connected the positive port to the input of the voltage regulator and am taking the negative of the main power supply as DGND. Is it wrong?

Yes I am using EVAL-AD7839EBZ evaluation board to test the AD7839. I am confused with the things that I need to connect in order to operate the DAC. I have attached all the links properly. when I connect the output of the TI controller to the evaluation board the voltage drops to 0.7 volts. Do I need to connect the WR, CS, and the LDAC signals?. And where do I need to connect the ground of the TI controller output signal. Previously I had connected it to pin no 22 of the evaluation board.

is it mandatory to use Clr and Ldac. To run the evaluation board?

You do not need to use LDAC. This pin is pulled to GND by a resistor so the pin can be left unconnected.

LK1 should be in position B to connect pin 29 (Vss on the AD7839) to the Vss supply.

CLR is connected to DB13 on the AD7839 evaluation board and this pin will need to be kept high when you are writing to the U4 latch.

For the supplies, you will need +15V connected to Vdd (J32-3), -15V on Vss (J32-1) and +5V on J31-1. GND should be connected to J32-2. You do not need a -5V supply.

To write to the DAC you will need to put data on the data bus DB0 to DB12. You have to do this in 3 stages by putting data on the parallel bus of the TI micro and pulsing the Latch Enable (LE) pins.

For example if you want to write 0b1110010101111 (13 bits of data) to the DAC you will need to do the following

1. Put 0b101111 on the TI uC bus and pulse LE1 low. This will put 0b101111 onto D0 to DB5 of the AD7839
2. Put 0b110010 on the TI uC bus and pulse LE2 low. This will put 0b101111 onto D6 to DB11 of the AD7839
3. Put 0bABC11 on the TI uC bus and pulse LE3 low. This will put 0b1 onto DB12 and set the CLR pin high (CLR is shown as DB13/CLR on the schematic). ABC are 1's or 0's depending on the values you want for A2, A1 and A0 and will select which DAC to update

  4. Pulse CS/WR to transfer the data to the DAC and the output should change.

Wat about the drop in the voltage from 3.2v to 0.7v? the voltage drops even when the circuit voltage is turned off.

What pins are dropping from 3.2V to 0.7V? As I said at the start, if you had Vcc=5V and GND=-5V you have probably damaged the AD7839 and the latches as these are 5V maximum devices.

Power up the eval board as described above and set a power supply to 3.2V. If you touch that 3.2V to any of the digital input pins on the 36 way connector and there's anything more than a few uA flowing then you've damaged the device.