KL03 time to wait after bandgap buffer is enabled

[martinkrause]

How long do I have to wait after enabling the bandgap buffer on an KL03 MCU before the read ADC value for the bandgap channel is stable? In the datasheet / user manual there is no time specified.

I'm asking, because when I do not wait any time, and just enable the bandgap buffer and then immediately afterwards do an ADC measurement of the bandgap, the ADC value "jumps" at higher MCU temeratures (> 50°C). If I add an delay of about 2 us, between enabling the bandgap buffer and measuring the internal bandgap voltage, the ADC value for the bandgap stops jumping, even at higher MCU temeratures (>80°C). My MCU runs at the 8 MHz internal clock, when I do this measurements, the ADC-Clock runs on ADC asynchronous clock source with ADLPC = 0 and ADHSC = 1.

So I assume, there is a waiting time after enabling the bandgap buffer, before I should do measue the ADC bandgap channel to get stable values. The question is how long should I wait to get stable values over the whole MCU temperature range?

Best Regards,
Martin

[kerryzhou]

Hi Martin Krause,

    Actually, we also don't have the bandgap voltage reference stable time, this time must be very small, but we don't have the precise data.

    Normally, If customer want to use the bandgap as the ADC input,  they can enable the bandgap before the ADC initialization, then the bandgap stable time must be enough.

    So, please try to enable PMC_REGSC[BGBE] bit before the ADC initialization code.

Wish it helps you!

If you still have question, please contact with me!
Have a great day,
Jingjing

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