topic Re: LPC55S69 : temperature measurement in LPC Microcontrollers

LPC55S69 : temperature measurement

EugeneHiihtaja — Wed, 04 Mar 2020 11:01:02 GMT

Hi !

I'm follow lpcadc_temperature measurement and fins out that whole ADC initialization. calibration and skip first samples take at list 10 ms. ADC clock is 12 Mhz in my case.

I measure temperature after wakeup from PowerDown mode and I think this time is too much.

I can see all ADC settings are set in way to garantie as accurate measurement as possible.

But what is not clear if internal temperature sensor must be handled with those settings or we can set more relaxing values for ADC ?

I have tried to set :

g_LpadcCommandConfigStruct.sampleTimeMode = kLPADC_SampleTimeADCK19;
g_LpadcCommandConfigStruct.hardwareAverageMode = kLPADC_HardwareAverageCount32; // + calibration at 32

and can see that total procession time is reduced a lot.

Could you recommend as fast as possible setting for ADC what acceptable for handling temperature sensor in reliable way in whole temperature range.

Regards,

Eugene

Re: LPC55S69 : temperature measurement

xiangjun_rong — Fri, 06 Mar 2020 08:56:27 GMT

Hi, Eugene,

Regarding the two parameters:

g_LpadcCommandConfigStruct.sampleTimeMode = kLPADC_SampleTimeADCK19;
g_LpadcCommandConfigStruct.hardwareAverageMode = kLPADC_HardwareAverageCount32; // + calibration at 32

For the g_LpadcCommandConfigStruct.sampleTimeMode variable, it is dependent on the external signal source impedance, the smaller the signal source impedance is, the small value the g_LpadcCommandConfigStruct.sampleTimeMode variable should take.

For the g_LpadcCommandConfigStruct.hardwareAverageMode variable, the ADC converter samples multiple times and compute an average value.

As you know that the temperature sensor is a high impedance and stable signal, so you should assign big value for the g_LpadcCommandConfigStruct.sampleTimeMode variable, and assign small value for the g_LpadcCommandConfigStruct.hardwareAverageMode variable.

This is my opinion.

Hope it camn help you

XiangJun Rong

Re: LPC55S69 : temperature measurement

EugeneHiihtaja — Fri, 06 Mar 2020 09:04:17 GMT

Hi xiangjun.rong‌ !

But can you suggest exact minimal values what garantie good result in whole temperature range and evaluated on NXP side ?

Regards,

Eugene

Re: LPC55S69 : temperature measurement

xiangjun_rong — Mon, 09 Mar 2020 02:39:57 GMT

Hi, Eugene,

Unfortunately, I can not give you the minimal value for the sample time parameter, because the temperature sensor impedance is not available.

XiangJun rong