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AD7616 Evaluation board in Standalone mode

Q: How can I setup EVAL-AD7616SDZ board to work as standalone, interfacing to MCU through SPI (without SDP).

A: EVAL-AD7616SDZ is designed to easily evaluate all features of both the AD7616. The evaluation board can be controlled by the EVALSDP-CB1Z via the 120-way high speed system demonstration platform (SDP-B) connector (J10) and the software GUI provided. If willing to use the EVAL-AD7616SDZ board, a series of modifications to the hardware might be needed. The following might be taken as a step-by-step guide.

1. Power-up the board

By plugging the input jack connector on J7, making sure LK41 and LK40 are at position A. Alternatively, AVDD and VDRIVE can be individually provided through J9 and J8, respectively. If doing so, LK41 and LK40 should be switched to position B.

Power Good LED should turn ON when supplies are applied. In addition, checking the voltage levels through the points listed with help of a multimeter ensures correct power-up.

Test Point

Pin Name

Pin No.

Voltage

VDD

AVDD

6-15-30-71

5.0V

VDRIVE

VDRIVE

49

3.3V

REGA

REGCAP

70

1.87V

REGD

REGCAPD

52

1.89V

J6

REFINOUT

33

2.5V

C28

REFCAP

31

4.096V

If the LDOS or Reference pins are not at their expected voltage level, AD7616 may be at reset state.

2. Take AD7616 out of RESET 

If leaving AD7616 RESET line at floating state, given SDP board is not connected, may lead to RESET active state. Tie RESET line to VDRIVE through J5-1and check again voltages in the table.

It is desirable to wire this signal to the MCU such that RESET can be user controlled.

3. ADC Conversion functionality

Once the supplies, LDOs, Reference and RESET lines are verified to be at the correct level, the ADC should be able to perform conversions by just issuing a rising edge on CNVST pin, available on J5-26.

Connect CNVST to MCU and monitor BUSY line, available on J5-25, with an oscilloscope or logic analyzer. BUSY line should go up after CNVST rising edge.

4. Data interface configuration

EVAL-AD7616SDZ, by default uses the parallel data interface. In order to use the serial interface, R64 needs to be removed and SL5 soldered down. With a multimeter, SER/PAR pin number 40 can be check with a multimeter to be at logic high level.

If willing to use only one SPI data output line, SER1W must be tied down. R61 can be replaced by a 0 ohm link to ensure this pin is always at logic low level.

Once verified the Serial Interface is set, we should be able to read ADC data on DOUT0. By doing two SPI writes through 16 bit frames, with MOSI line low, DOUT0 should clock out V0A and V0B data. It’s recommended to remove the resistors going from J5 to J10 (e.g. R87, R90, R91, etc) to avoid any line being pulled unintentionally.

In order to verify these are the channels being clocked out, change the corresponding jumpers that tie the negative inputs to ground. One at a time, if LK1 is removed, the first 16b word would change to reading near 0x0000 (because both inputs on V0A are now floating).

If LK9 is removed instead, the second 16b word will show the near 0x0000 reading.

5. SPI Register Reading

In order to verify the interface connections, start reading registers and check their default values. First of all, AD7616 should be in Software mode. To do so, make sure LK36 and LK37 are at C position, i.e. tied to ground. The state of this pins after a Full Reset will dictate the mode of operation. So, issue a full reset and wait the 15ms device setup time before reading registers.

6. SPI Register Writing

Next step would be to perform a register write, then verify the SPI transaction is properly done. An easy one to use is to enable the Interface Check feature. To do so, 0x86BB needs to be written on the SPI interface, before starting to read ADC data.

Subsequent ADC reads, in between conversions, will clock out 0xAAAA in channel A and 0x5555 in channel B.

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