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Injected ADC Conversion Time off by 1.2usec

Question asked by grace.richard on Feb 20, 2014
Latest reply on Feb 20, 2014 by grace.richard
I am using TIM1 (PWM Mode) to trigger injected adc conversions in dual mode.  The ADC clock is set to 72 Mhz (PLL Clock).   The ADC sampling is set to 19.5 cycles --> a total conversion time of 19.5 + 12.5 = 32 cycles = 444 nsec.   For N channels the JEOS interrupt should occur at N * 444 nsec after the rising edge of the PWM.   

The problem is that the JEOS interrupt occurs at N * 1.68 usec after the rising edge of the PWM. I have tried this for 1,2 and 3 ADC conversions in the sequence. 

I have confirmed the correct clock by calling RCC_GetClocksFreq().  I also changed the sampling from 19.5 cycles to 61.5 cycles and the time from PWM rising edge  to  JEOS changed by the appropriate amount - 578 nsec. 

Does anyone know what's causing the 1.2usec delay in the ADC conversion