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AD7612 Providing No Output

Question asked by someGuy on Jul 8, 2015
Latest reply on Jul 13, 2015 by someGuy


I have recently purchased the AD7612 for evaluation. I intend to deploy the ADC into a system I am designing but am having trouble getting a response from the device. I currently have the AD7612 soldered on a custom PCB with the arrangement depicted in Figure 1 (see attachments). As I understand the datasheet and given the current state of my schematic, the AD7612 is operating in the following mode/conditions:

Mode –

Digitial Output Type: Straight Binary

Output Mode: Parallel

Conversion Mode: Impulse

Input Range: 0V to 5V

Reference: Internal

Reference Buffer: Internal

Conditions –

(AGND, Pin 1): PCB Ground

(AVDD, Pin 2): PCB +5V

(AGND, Pin 3): PCB Ground

(BYTESWAP, Pin 4): PCB Ground

(OB/2C, Pin 5): PCB +5V

(WARP, Pin 6): PCB Ground

(IMPULSE, Pin 7): PCB +5V

(SER/PAR, Pin 8): PCB Ground

(D0, Pin 9): D0

(D1, Pin 10): D1

(D2, Pin 11): D2

(D3, Pin 12): D3

(D4, Pin 13): D4

(D5, Pin 14): D5

(D6, Pin 15): D6

(D7, Pin 16): D7

(OGND, Pin 17): PCB Ground

(OVDD, Pin 18): PCB +5V

(DVDD, Pin 19): Coupled to PCB+5V through network similar to Figure 27 of AD7612 datasheet, page 19 Note 5.

(DGND, Pin 20): PCB Ground

(D8, Pin 21): D8

(D9, Pin 22): D9

(D10, Pin 23): D10

(D11, Pin 24): D11

(D12, Pin 25): D12

(D13, Pin 26): D13

(D14, Pin 27): D14

(D15, Pin 28): D15

(BUSY, Pin 29): Output monitored by oscilloscope during debug.

(TEN, Pin 30): PCB Ground

(RD, Pin 31): PCB Ground

(CS, Pin 32): PCB Ground

(RESET, Pin 33): PCB Ground

(PD, Pin 34): PCB Ground

(CNVST, Pin 35): Input signal fed from function generator during debug. 100kHz, 5Vpp, 2.5Vdc offset, 80% duty cycle, square wave.

(BIPOLAR, Pin 36): PCB Ground

(REF, Pin 37): Output pin monitored via DMM.

(REFGND, Pin 38): PCB Ground

(IN-, Pin 39): PCB Ground

(VCC, Pin 40): PCB +7V

(VEE, Pin 41): PCB Ground

(AGND, Pin 42): PCB Ground

(IN+, Pin 43): Input signal fed from function generator during debug. 10kHz, 3Vpp, 2.5Vdc offset, sine wave.

(AVDD, Pin 44): PCB +5V

(TEMP, Pin 45): No connect

(REBUFIN, Pin 46): Tied to PCB Ground via 100nF capacitor as in Figure 27 of AD7612 datasheet, page 19 Note 5.

(PDREF, Pin 47): PCB Ground

(PDBUF, Pin 48): PCB Ground

(EPAD, Pin 49): PCB Ground

The PCB has a single ground, a +5V rail, and a +7V rail. I’m using function generators to provide CNVST/IN+ to the AD7612 and am monitoring the output of D[0:15] with a logic probe. I am also monitoring the BUSY pin and CNVST pins on an oscilloscope. For the time being, the amplifier depicted in the schematic is removed and not physically connected to the IN+ pin. I have ran a full continuity check on each pin, checked the voltage at each configuration pin, verified that there are no short-circuits (using a high-power microscope and by running a second exhaustive continuity test). Additionally, when the AD7612 is powered on I have ~110mA of current draw through the +5V rail and ~1mA of current through the +7V rail. When I tie the PD pin high, the currents drop to ~(3mA,1mA) respectively. This drop in current seems to indicate that the device is at least responding to input but 110mA seems high given the values in the datasheet. On the D[0:15] output I have no activity (i.e. the signals remain low), and the BUSY pin goes high and remains there after power-up. Lastly, when the voltage at the REF pin is measured, I am getting 4.7V which seems inconsistent given that the datasheet specifies that this pin should be at +5V when the internal ref and buffer are used.

Can anyone provide any insight as to why I am not getting a response from the AD7612?

Does the voltage at REF seem consistent?

Does the current draw seem consistent?

Is there an issue with how I have the AD7612 configured?

Any help and insight is much appreciated.