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AD7606C-18: FAQs

Q: What’s the difference between the AD7608 or AD7609 and the AD7606C-18?

The AD7606C-18 is a directly pin replacement (software and hardware) for both AD7608 and AD7609, with higher input impedance, throughput rate and extended temperature range, see A.N. 2078 for further details on how to migrate from AD7606 design into AD7606B.

However, by writing to its memory map, a series of advanced features can be enabled:

-system gain/offset/phase calibration,

-per channel analog input range selection with bipolar differential, bipolar single-ended and unipolar single-ended options,

-sensor disconnect detection

-additional oversampling ratios

-lower Vdrive operation

-diagnostics

Q: What sort of errors can be detected through AD7606C-18 diagnostic features?

The AD7606C-18 diagnostic features can be enabled to detect individually several errors like:

-an inadverted reset,

-and spi read/write error,

-memory map or rom corruption,

-busy line getting stuck

In addition, a diagnostic mux, allows to dedicate any channel to measure internal nodes like supplies, reference, LDOS or a temperature sensor

Q: What are the benefits of turning oversampling mode on in the AD7606C-18?

By turning on the oversampling mode, the noise performance is improved. AD7606C-18 allows up to 256 oversampling ratio in software mode. Note that the maximum throughput rate scales down with the oversampling ratio, being 1 MSPS/OSR. Check the Software model in the AD7606C-18 product page to see how OSR improves noise performance and limits the throughput.

AD7606C-18 ACE remote control wiki page shows how to easily check this feature if the AD7606C-18 is available.

Q: I have a series resistor in front of my analog inputs that causes a gain error, how can I calibrate this gain error off with AD7606C-18?

Having a series resistor in front of the ADC leads to having a system gain error. This system gain could be calibrated on the backend, however the AD7606C-18 provides a feature to compensate this error by just programming the resistor value used on the front-end (up to 65kOhm). This gain calibration register reduces the burden of doing this task on the backend, and achieves it more precisely because the it uses the actual, factory trimmed, input impedance on each device. See A.N. 2011 for further details on AD7606B gain calibration feature, and simulate it through the Software model  available on the product page.

Q: How does the offset or phase calibration work, what range and resolution do they achieve?

The offset calibration allows to add or subtract up to 512LSB to the ADC conversion result with a resolution of 4LSBs, in order to compensate for any known offset error on the front end (e.g. external resistor mismatch).

The phase calibration feature allows to delay, on any channel, the sampling instant up to 255 us, with a resolution of 1us.

These features can be simulated through the  Software model available on the AD7606B product page.

 

Q: What is the sensor disconnect detection feature implemented on AD7606C-18 and how does it work?

The sensor disconnect detection, if enabled, alerts automatically when the input signal gets disconnected from the ADC analog inputs.  Alternatively, this feature can be used in manual mode. See A.N. 2011 for further details on how each mode works and how the implemented algorithm works.

 

Q: What AD7606C-18 output code should I expect if the analog input pin is left floating?

It is good practice tying to ground any unused analog input pin. However, if the Vx pin is floating while the Vx- is tied to ground, the ADC result will be as per table below.

Note these values and are only an approximation, analog input pins are susceptible to any kind of noise being coupled in.

 

ADC CODE 

ADC (V)

±2.5V Single-Ended

65841

1.25

±5V Single-Ended

42974

1.63

±6.25V Single-Ended

36852

1.75

±10V Single-Ended

25340 1.93
±12.5V Single-Ended 21104 2.01
0 to 5V Single-Ended 65801 1.25
0 to 10V Single-Ended 48950 1.86
0 to 12.5V Single-Ended 40726 1.94
±5V Differential 43027 1.64
±10V Differential 25387 1.93
±12.5V Differential 21159 2.01
±20V Differential 13941 2.12
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