MCU power consumption calculation ???

[epp]

power and calculation

Hi!
How can I determine total current consumption of an MCU-DSP etc?
I have read from datasheets for dsPIC (30MIPS, 16xPLL, 5V, 25degC, PDIP40) that its Idd is 132mA at that conditions and that its maximum consumption current on all ports (from absolute maximum ratings) is 200mA.
Is my total consumption current sum of these two currents or
only one greater than other?

I need that in order to find appropriate heatsink for LM7805 (Vin=15/Vout=5V).
Thanks.
Regards.

 

[Davood Amerion]

power calculation for mcu

132mA consumption is forever, and not depend on I/O PIN.
you can calculate average current consumption on all I/O pins and add that value to this(132mA) value

for regulator it is better to use switching one, like LM2575 (from national), or MC34063 (from motorolla)

Regards,
davood Amerion

 

[VVV]

mcu power consumption

The Idd value is needed by the core. To that you need to add the I/O power consumption. But you should not take any values from Absolute Maximum Ratings, because they only tell you when the part gets fried, so these are values you should be careful not to exceed under any conditions.

You should go through the I/O lines and see what's connected to each and figure out the actual current. Where you have I/O lines that switch relatively fast, you need to account for that using the capacitance and the actual switching frequency.
For example, if the total capacitance connected to an I/O line is 20pF and you toggle it at 1MHz, then that single I/O line will draw an average current:
I=Vdd*C*fsw=5*20E-12*1E6=0.1mA (this is just for switching, any DC current must be added to this). Add all the currents of all I/O lines to Idd.

Perhaps the safest way is to actually measure the supply current while the part is operating.

 

[IanP]

power calculation mcu

Perhaps the safest way is to actually measure the supply current while the part is operating.

Yes, this is what I would do .. calculations/estimations are highly inaccurate ..

Regards,
IanP

 

[bobsanjose]

dspic33f power consumption

First of all, you can get 60 MIPS with less than 60 mA if you don't use dsPIC but an ARM7.
Second, Idd is what the microcontroller maximum uses, that does include but is not limited to the core. All peripherals such as timers, serial interfaces and so on also consume power and that power is (usually) included in Iddmax.
On top of Idd, you can drive external loads by sinking / sourcing current through port pins. Adding up all absolute values of those sink and source currents must not exceed the 200mA, otherwise the device will such an early end of live.
For you heat sink, it is actually important to look at both BUT measure your current and you will probably see less than the max Idd all together unless you drive several LEDs directly with the port pins.
All in all the dsPIC seams to be a device that uses way too much power for what the performance is.
Think about ARM.

Bob