Chapter 1 Device Overview MC9S12ZVMB-FamilyMC9S12ZVMB Family Reference Manual Rev. 1.3NXP Semiconductors 59Furthermore the production test temperature control accuracy is limited to +/-3C. Figure 1-7 illustratesthe effect of this limitation, whereby the value V26 actually corresponds to a test temperature of 29C.Thus, if configured to detect V26 + 600mV, the detection could be offset by 3C and in this case wouldoccur at 129C for a typical slope. Considering further inaccuracy for the minimum slope results in anactual temperature limit detection at 132.3C as shown in Figure 1-7. Further compensation can beapplied, if necessary by adjusting the detection level.Figure 1-7. Effect of slope plus V 26 reference inaccuracyThe ADC uses the on chip generated VDDA as the VRH reference. The accuracy of VRH can also beconsidered. In order to compensate for VRH load variation, the reference voltage can be indirectlymeasured using the internal reference voltage VBG. VBG is mapped to ADC channel internal_1. Thus aVRH reference can be obtained by applying a clean, unloaded VRH and converting V BG. The resultingADC conversion result of VBG can be stored to flash for reference.By measuring the voltage VBG in the application environment and comparing the result to the referencevalue stored in flash, it is possible to determine the current ADC reference voltage VRH:Voltage (V)Temperature (C)29V261266 mV/C5.8 mV/C0.6 V0.562 V12926Typical slope from V26Typical offset slope from V 26Minimum dV/dT offset slope from V 26132.3
