Kinetis MicrocontrollersのトピックRe: VREF vs bandgap voltage reference (aka system reference voltage)

VREF vs bandgap voltage reference (aka system reference voltage)

robertpoor — Mon, 16 Jan 2017 21:11:12 GMT

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?)

Re: VREF vs bandgap voltage reference (aka system reference voltage)

Hui_Ma — Tue, 17 Jan 2017 07:06:44 GMT

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:

Wish it helps.

Have a great day,
Ma Hui
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Re: VREF vs bandgap voltage reference (aka system reference voltage)

egoodii — Tue, 17 Jan 2017 15:11:57 GMT

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!