KE02: Bandgap Reference: Temperature Characterization

colin_campbell — Tue, 29 Oct 2019 02:38:43 GMT

Hi NXP,

The KE02 includes a Bandgap Reference with a nominal trimmed value of 1.16 Vdc at 25C, but the Data Sheet (Rev.5, 01/2019) provides no indication on its value over the operating temperature range of the device (we are using the MKE02Z64VFM4) – could you please provide a response to the following questions:

What is the expected range of Bandgap Reference values at the maximum ambient operating temperature of 105C (e.g. 25C Nominal +/- 2%)?
What is the Temperature Coefficient of the Bandgap Reference?
Do you have an Application Note providing details of a KE02 based Internal Temperature Measurement carried out using the Bandgap Reference?

Thank you for the assistance - CC

Re: KE02: Bandgap Reference: Temperature Characterization

mjbcswitzerland — Tue, 29 Oct 2019 12:13:49 GMT

For temperature sensing one normally uses the temperature sensor in the 12 bit ADC rather than the band-gap reference (which is usually designed to be as temperature insensitive as possible).

The ADC temperature sensor is specified:

and reference code to convert to temperature is

                    #define VTEMP_25_16BIT               ((VTEMP_25_MV * 0xffff) / ADC_REFERENCE_VOLTAGE)
                    #define VTEMP_25_12BIT               (VTEMP_25_16BIT >> 4)
                    #define VTEMP_25_10BIT               (VTEMP_25_16BIT >> 6)
                    #define TEMP_SENSOR_SLOPE_100_16BIT ((TEMP_SENSOR_SLOPE_UV * 0xffff)/(10 * ADC_REFERENCE_VOLTAGE))
                    #define TEMP_SENSOR_SLOPE_100_12BIT (TEMP_SENSOR_SLOPE_100_16BIT >> 4)
                    #define TEMP_SENSOR_SLOPE_100_10BIT (TEMP_SENSOR_SLOPE_100_16BIT >> 6)
                    if (ADC_TRIGGER == ucInputMessage[MSG_INTERRUPT_EVENT]) { // convert the ADC reading to a temperature
                        signed short ssDifference = (results.sADC_value[0] - VTEMP_25_12BIT); // convert references to 12 bit values
                        signed long slTemperature100 = (2550 - ((ssDifference * 10000) / TEMP_SENSOR_SLOPE_100_12BIT)); // the approximate temperature *100, rounded up/down
                        slTemperature100 /= 100;                         // the approximate temperature rounded up/down to 1°C
                        fnDebugDec(slTemperature100, DISPLAY_NEGATIVE);
                        fnDebugMsg(" degC\r\n");
                    }

where (for KE02)

#define ADC_REFERENCE_VOLTAGE 5000 // ADC uses 5.0V reference

#define VTEMP_25_MV 1396 // typical internal temperature sensor reference voltage (in mV) (5.0V VDD/VREF and < 3MHz ADC clock speed)
#define TEMP_SENSOR_SLOPE_UV 3260 // typical internal temperature sensor slope uV/°C (5.0V VDD/VREF and < 3MHz ADC clock speed)

Regards

Mark

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Re: KE02: Bandgap Reference: Temperature Characterization

colin_campbell — Wed, 30 Oct 2019 21:21:20 GMT

Hi Mark,

Thanks for the quick update and reference code - that all makes sense.

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KE02: Bandgap Reference: Temperature Characterization

Re: KE02: Bandgap Reference: Temperature Characterization

Re: KE02: Bandgap Reference: Temperature Characterization