I am using ADC IC (ADAS3023BCPZ) which is working for only 20 to 30 minutes; after that it gets heated-up by drawing more current from the supply.
Used Supply details -
VDDH -> +15V ; VSSH -> -15V ; AVDD,DVDD -> +5V ; VIO -> 3.3V
Only difference in schematic with respect to datasheet is - EP(Exposed Pad) is connected to AGND in my board instead of VSSH.
Is this the reason for heating-up the IC after some minutes ?
Please clarify on this point.
Apology for the late response. No difference on EP(Exposed Pad) connected to AGND, instead of VSSH. I'd like to know if there other components use or connected on the supplies(+-15V and +5V)? Something draws a lot of current. It would be helpful if you can share the schematic.
Thanks for your reply..
Find the attached schematic; but in datasheet its mentioned that connect EP to VSSH only.
Please review the schematic & suggest solution.
Find the attached image captured in CRO..
Thanks for the scope shot. Please confirm if the ch2 on the scope shot is the CNV pin? if yes. this setup will only read/convert the ch0 of the ADC. A conversion is initiated on the rising edge of the CNV pin. you can held this high or low until such time (16sclk times the number of channels) before putting again the rising edge of the CNV pin.as shown on the general timing on the datasheet.
Ch-2 is not CNV pin ; that is SDO. As I mentioned before I am reading same output at SDO .
One more thing I observed that at power-up ,digital isolator output is high for appr.14msec (sch attached in previous reply) . is it creating problem for ADC communication ?
Waiting for your reply..
Apology for taking late response. I have to check few things just to confirm.
1. This should be corrected. the exposed paddle MUST be connected to VSSH as this is the lowest potential in the circuit and avoid permanent damaged to the device.
2. From your schematic PD(digital inputs) is not connected. This should be tied low. Can you check to see the voltage at ACAP(26)and DCAP(25). If these are not approximately 2.5V to 2.6V then it indicates the ADC may be in shutdown mode.
3. Since you are using the internal reference can you verify the voltages.
4. additionally we would recommend
a. 100K weak pull up to 3.3V supply rail to CS,CNV and RESET pins.
b. 100K to DGND to PD at a minimum or I would however prefer to add the isolated driver for PD and a weak pull up to 3.3V supply as well.
If you could provide a PDF of the supply decoupling and connectivity for the ADAS3023 it would be helpful.
It would also be helpful to see the power up sequence scope shots.
Finally a scope shots of the digital activity for the first conversion and subsequent conversions would be very helpful as well.
Thanks and Best regards,
Find below comments for your query & attached pdf (schematic, waveform measured using CRO & logic analyzer).
Note - Previously because of wrong connection of EP, we made a separate pcb for ADC & connected to the main board using discrete wire -> that time signal at SDO was high irrespective of input signal)
In main board, we made a hole for EP & connected it to VSSH externally as it was connected to GND point in main board. Now the signal at SDO is fluctuating irrespective of input signal after mounting ADC in main board.
Below points are after mounting ADC in main board.
1. Exposed pad connected to VSSH.
2. I have tested with PD low as well as controlling PD via microcontroller -> in both the case, data at SDO is fluctuating.
3.Find the voltages monitored at different points:
REFIN -> 2.53V , REF1/REF2 -> 4.30V , ACAP -> 2.59V , RCAP -> 2.57V , DCAP -> 2.60V
4. Pull-up 100K connected at CS,CNV,RESET,PD and tested, but data at SDO is varying with or without input signal.
Find the attached images.
I thought ADC may be not working & so tested with new ADC, but data at SDO still varying.
Also checked at CLK frequency 30MHz, 15MHz, 1 MHz...still no improvement.
Looking for your suggestion immediately.
Can you resend the pdf schematic file. I can't find on the attached file.
waiting for your reply..
Can you elaborate please what you mean by with or without input? I'm not sure I understand.
Are you initiating a conversion by asserting a convert start pulse? if so what is the timing of this signal relative to the serial communications?
also I can't find the pdf schematic as you mention on the attached file.can you send this again as well.