Calibration process

[shermantec]

Posted on July 18, 2003 at 11:05

Calibration process

[shermantec]

Posted on July 10, 2003 at 09:08

I have some technical question I think beyond the scope of the ST Forum

All regarding the internal oscillator and its calibration The manufacturer supplies two factory calibration values for 5V, 1MHZ and 3V, 700 KHz 1) Are this values written into the EEPROM when the calibration process just reach the 1% percent of accuracy or they try to get the closest value to the reference frequency, 1MHz for 5V and 700KHz for 3V? I ask this question because from my experience with the ST7LITE05 when I use the calibration value, the received frequency is into the 1% limits but if I carry out further iterations I can reach even better results. It will help for frequency shift with temperature. For laboratory tests it is OK to do some iterations but for production I'd prefer to be able to use the factory calibration values as is and to avoid any calibration procedure in the mass production line. 2) We are talking about very large quantities of MCU's. Can we in this case choose other voltage values for the supplied calibration values, let's say 5.5V and 4.5V for 1 MHz both instead of 5V and 3V ? This will cover the entire range of battery voltages during the product life span. 3) Do they carry out the calibration process with the chip in Die form also as we are going to use it ? As far as I'll be able to know and understand the factory calibration process I will be able to reflect this in the application code I am writing and we will make the necessary arrangements for production, including all kind of test. Some of them I have to introduce in my code as monitor routines to be used in the production line. So I need the most detailed information about all this. Latino

[stephanie]

Posted on July 18, 2003 at 11:05

Hi,

1) the calibration done after the final test are done to get the closest value to the reference frequency. The accuracy reached is +-0.35%. A final read of the stored values are done to check this range. 2) Default values stored are 1MHz for 5V +25°C and 700kHz for 3V 25°C. Explanations concerning accuracy variation depending on the Vdd or t° are in the datasheet: between Vdd=4.5 to 5.5V, accuracy is +-1% but still at 25°C. At 5V but on the whole temperature range, accuracy is then -5/+2%. Up to the user to choose his own conditions and to recalibrate the RC thanks to AN1324 for instance! 3) Concerning the die form, a first calibration is done on wafers to screen parts but after the assembly, the calibration values change. The final calibration is done only after the packaging (during final test). For die form, it will be up to the user to calibrate the RC (add a small s/w in their application for instance: AN1324).