Hello, i have an application, where the AD5270 should set a voltage inside a LDO-circuit, but the Wiper-position doesnt change from the mid-scale. The commands i sent are:0x1C030x0407(random data, to test the RDAC)
The SIMO, SCLK, and the SYNC signals are measured right at the Pins of the AD5270. In the figure the red signal is SYNC, the yellow one is the Clock, the green one is the DIN and the blue one is the SDO. I also tested the code 0x2400, to set the software shutdown to normal, which didnt work either.
Is there anything i have missed out to get the RDAC working?
Thanks in advance.
Ok i found my mistake and it works fine now. The SDO Pin of the device had a pull down resistor not a pull up resistor. Next time i should read the Data sheet a bit more detailed.Thanks for your time,…
Please share the schematic and the supply details.
The AD5270 is supplied with 5V (provided by a Zener Diode) on VDD and the VSS and GND Pins are connected to the board ground reference(DUT_S), as seen in the schematic below.
The LT3082 sets a voltage on the output depending on the resistance between the Set-Pin and GND(V_out=10µA*R). The AD5270 is planned to be in series with those 1.8MOhm resistors(just one of the resistors will be soldered onto the board), to adjust the Output-Voltage between 18V and 19V.
The SPI Master in this case is the TMS320x28335 from Texas Instruments.
How is the LDO getting powered.?
What is the voltage on SET pin and DUT_S output?
The LDO is getting powered by a 24V Potential on the In-Pin (not pictured in the schematic). The 24V Potential is provided by a 1W DC-DC-converter.
The voltage between the Set Pin and DUT_S is round about 17V. 0.5V drop between Terminal A and W and 16.5V drop across the resistor (which is actually a 2MOhm resistor instead of a 1.8MOhm one). The output voltage with the 2MOhm resistor and the AD5270 in midscale is at around 20.5V.
Can you please provide details on the AD5270 VDD connection? How much current is being supplied by the Zener diode to VDD and what is the VDD voltage and current profile during idle and active states?