VREF vs bandgap voltage reference (aka system reference voltage)

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VREF vs bandgap voltage reference (aka system reference voltage)

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robertpoor
Senior Contributor I

On a processors such as the KL27 family, either the bandgap voltage reference or  VREF can be used as reference inputs to the ADC.  This leads to two questions:

  • Since VREF is actually derived from the bandgap voltage reference, when (and why) would you use VREF as a reference input rather than the bandgap voltage reference?
  • What is the bandgap voltage?  Some documents suggest that it is 1.0 V, other documents suggest that it's 1.2V.  (I guess the real question is: where do I find the electrical specifications for the KL27 family of processors, in particular Vbe?)
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egoodii
Senior Contributor III

Internal bandgap cannot be internally selected as any 'direct' ADC reference --- you CAN 'promptly' convert the bandgap alongside your analog-of-interest and 'calculate back' the 'true' value of Vref at the moment, BUT note that the Kinetis internal bandgaps are only rated +/-3% (as noted in the datasheet Vbg), and even a good NCP1117 (or similar 2% part) Vdd regulator would be better than that, without this extra step!

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Hui_Ma
NXP TechSupport
NXP TechSupport

Hi

1> The Bandgap voltage (PMC module provided) could not be used as ADC reference voltage, while VREF module provides VREF_OUT pin could be working as ADC module reference voltage. The ADC module channel 27 listed Bandgap is PMC bandgap 1V reference voltage.

2>  The PMC bandgap voltage is listed at Table 6 of KL27 datasheet:

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Wish it helps.

Have a great day,
Ma Hui
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