SDADC Gain 0.5 max Vin?

[valentin]

Posted on December 08, 2015 at 22:02

Hi,

According to AN4207 page 10, in Single ended zero ref mode the max input voltage to the ADC is Vref/gain. So if I set Vref = 3.3V = VCC, can I measure up to 6.6V with gain = 0.5? Or would this collide with the max voltage requirements of the pins (= 3.6V)? Reason I'm asking is that I need to measure a 0 - 5V signal (high impedance, from a pot) and want to use the SDADC for that if possible to achieve 16 bit accuracy. #sdadc-gain-0.5-max-voltage

[raptorhal2]

Posted on December 09, 2015 at 02:29

No.

Yes. Your homework assignment is to read the device data sheet and report back what the abbreviation ''TTa'' stands for. For your graduation thesis, report back why the lowest gain is 0.5. Cheers, Hal

[valentin]

Posted on December 09, 2015 at 03:26

Well that's the whole point why I'm asking as TTa/TC pins only allow up to 4.0V as absolute maximums.

The thought behind the question though is, whether that only applies to AFTER the 0.5 gain as that is what AN4207 implies ... Nice comments about homework and graduating btw. That stuff surely helps to keep the thread on topic.

[John F.]

Posted on December 09, 2015 at 09:19

Absolute Maximum  trumps everything else.

As the Datasheet note tells you, ''VIN maximum must always be respected. Refer to Table 20: Current characteristics for the maximum allowed injected current values.'' The ADC inputs are described as 3.3V tolerant with an Absolute Maximum range of Input voltage on TTa pins (VSS − 0.3) .. 4.0 Volts. Setting Gain to 0.5 does not give you greater electrical input voltage range!  

[valentin]

Posted on December 09, 2015 at 20:05

Cheers!

That's exactly what I wanted to know. Will go for an LTC2452 then 🙂