Does F28335 really NOT support Bipolar ADC??

Qian Cheng

Other Parts Discussed in Thread: TMS320F28335, UA741

Hi,everyone:

I have read some reference guides of F28335, I found that the pin ADCLO has been (or has to be) connected the analog ground. Does it mean that F28335 cannot do negative-voltage ADC?

For example, I want to converte -1.5~+1.5V, must I build a signal conditional circuit to offset the input voltage, as Teaching Guide suggests:

I just want to make sure of this. I don't want to build a lot of OpAm circuits in vain.

Thanks!!

over 15 years ago

0 BrandonAzbell over 15 years ago

TI__Guru 64650 points

Yes, this is correct. You will need to condition the signal to offset the input voltage to an acceptable range.

Electrical characteristics of the ADC can be found in Table 6-50 of the TMS320F28335 datasheet.

0 Qian Cheng over 15 years ago in reply to BrandonAzbell

Prodigy 180 points

Thank you very much

I think 2 or 3 uA741 Op-Am will handle this. I have 4 analog input in my design, which means I will use 8-12 uA741 chips. Does TI sell netagive-voltage generator chips? If so, would you please recommand some types which has strong sink/source current capabilty to drive 12 Op-Am?

Best wishes

0 BrandonAzbell over 15 years ago in reply to Qian Cheng

TI__Guru 64650 points

What is your input supply voltage range?

What is the desired negative output voltage?

How much current needs to be supplied?

0 Qian Cheng over 15 years ago in reply to BrandonAzbell

Prodigy 180 points

Hi,

I have bought F28335 Experiment Kit now. This kit can provide 3.3V and 5V voltage. I think, in order to let the Op-Am work well, the negative-voltage chip may be able to provide nearly -5V. By datasheet, typical supply current of uA741 is 1.7mA while maximum value is 2.8mA. Assuming I need 12 uA741 in conditional circuit , the the negative-voltage chip had better provide 36mA to make sure that Op-Am can work.

I hope TI can proveide satisfactory product. Thank you.

0 BrandonAzbell over 15 years ago in reply to Qian Cheng

TI__Guru 64650 points

There are a number of inverting regulator products.

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=754&uiTemplateId=NODE_STRY_PGE_T&paramCriteria=no

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Does F28335 really NOT support Bipolar ADC??