AnsweredAssumed Answered

AD5422 PwrOn ramp, Overrange feature

Question asked by Daniel_M on Dec 8, 2014
Latest reply on Dec 10, 2014 by Daniel_M

Hi,

we now have designed out hardware with AD5422LFCSP, but it's not yet manufactured. We decided to use the internal DVcc (DVccSEL left open).

So, my first question is:

1. Does the internal DVcc switch on later and sequence correctly to ensure that the internal calibration is done as described in p.29 of the rev.J datasheet, so that a software reset is not necessary? At DVcc theres a capacitor of 100nF, At both AVss and AVcc 10µF and 100nF (dual supply).

 

2. We like to use the Overrange-feature for the voltage output. We want to offer both unipolar and bipolar output options for our users.

2.1. If the output range is unipolar, e.g. 0..10V, does the overrange feature mean, that for CODE ("D")=0 the output voltage is also =0V, so negative values like -1V can't be reached, even with bipolar supply (AVss= -12V, AVdd= +12V)?

So, the overrange does only apply to the voltage of the full-scale code (0xFFFF) or also to the zero-scale output?

In other words, can I change the "gain" parameter in the equations on p.29 to +10% (e.g. gain value = 2.2 instead of 2 for 0..10V)?

2.2. Do the good TUE values listed in the "typical performance characteristics" also apply with the OVRRNG-Bit=1?

In other words, for example, can I refer the TUE for 5V output (at D=0xFFFF: -0.007%) directly to 5.5V with OVRRNG=1?

2.3. On p. 33, it's written: "When enabled via the control register, the selected output range is overranged by, typically, 10%."

What does this "typically" exactly mean? What is its maximum deviation?

 

To get you to know why I need to know that: I'n just doing some considerations regarding the software. If the overall precision is the same with overrrange feature (and the OVR is quite exactly 10%), I don't need variable calibration values, and at production we don't need to calibrate the outputs. Otherwise, we need them and that would be costly in calibration time and also in memory space, since we're designing an eight-channel device with 8 AD5422 in daisy-chain configuration.

Outcomes