Canvas D Question 3 Consider designing ded system using a PIC32 running at 30 MH

Question

Canvas D Question 3 Consider designing ded system using a PIC32 running at 30 MHz Using the table below, what percentage of the time (to three decimal places) must the processor be in the Power Dow mode if the rest of the time it is in Normal run mode and you wish the average current draw to be no more than 8.871 n Assume the processor will un at 25 deg. C, typical current draws are used, and no Watchdog, RTCC, or ADC is running TABLE 30& DC CHARACTERISTICS: OPERAT?NG CURRENT(OO) standard Operating Conditions:2.3V to S.6 (unless otherwise stated Operating temperature 40°C S TA S +85'C for Industrial DC CHARAC TERIS TICs 40'C S TA S +105'C for Vtemp Parameter vpicalMax. Units Conditions Operating Current (loo) (Notes 1,2,5 DC20 DC21 DC22 OC23 | 15 23 mA MHz (Note 4) 105 15 mA 10 MHz 20 MHZ (Note 4 30 MHz (Note 4 40 MHz 10 TABLE 30-6: DCCHARACTERISTICS IDLE CURRENT(IOLEL_

Explanation / Answer

the information which can be extracted from the question

1- Processor temperature -25°C

2- typical value of current to be used

3- no Watchdog, RTCC or ADC is running

4- 30Mhz operation

5- avg current consumption should be less than 8.871 mA = 8871 uA

hence the information can be found from tables

a) IItypical,Normal = 15mA = 15000 uA

b) IIItypicaI, Power down = 44uA

let the system runs in Power down mode. = x% of time

let the system runs in Normal mode = (100-x)% of time

hence the equation becomes (by calculating average)

((100-x)*15000 + 44*x )/100 <= 8871

=> 1500000 - 15000*x +44*x <= 887100

=> 612900 -14956*x <= 0

=> x >= 40.980 % of time in power down mode

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