ee3954_fall13_10_adc

624 therefore tc 165 s adc33 finding time for

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Unformatted text preview: Tc = - (120 * 10-12)( 10,000 + 1,000 + 7,000) * ln (1/2047) Tc = - (120 * 10 -12)*(18,000)*(-7.624) Therefore: Tc = 16.5 µs ADC.33 Finding Time for Temperature Coefficient Term (Tcoff) : Tcoff = (Operating Temp in °C - 25°C)*(0.05µs/°C) Lets assume worst case Operating Temperature is 50°C (= 122°F) Tcoff = (50°C - 25°C)*(0.05µs/°C) Therefore: Tcoff = 1.25 µs ADC.34 So total Acquisition time Tacq = Tacq = Tamp + Tc + Tcoff Tacq = 2 µs + 16.5 µs + 1.25 µs Tacq = 19.75 µs With our 4 MHz PIC’s in lab – (1 µs instruction cycle) We would delay 20 µs before we start conversion (GO is set) ADC.35 ADC Timing … 19.75 µs (example) ADC.36 ADC Conversion Time for Successive Approx. Converter Takes 11.5 TAD for conversion Successive Approximation TAD must be ≥ 1.6µs ADC.37 Selecting TAD Clock Source Value Using PIC’s in Lab: Minimum TAD must be ≥ 1.6 µs PIC’s in Lab use 4 MHz oscillator, so Tosc = 0.250 µs We need to set ADCS1, ADCS0 bits in ADCON0 to select TAD: ADCS1,ADCS0 0 0 0 1 1 0 1 1 Ope...
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This document was uploaded on 01/22/2014.

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