# How to estimate current consumption by ICs

I'm using an Arduino Due (3.3V) which has a maximum current for all pins 130mA.

How to estimate consumption for a number of ICs?

For an example i use multiple MCP4822 (2channel DAC)

On the datasheet I read "input current" 415-750 μΑ.

But what current the SPI clock signal and the MISO signal consume?

If i connect several ICs does this drains more current?

Does this DAC consumes so small current that i connect as many as i like?

EDIT: or please only a general guidance: how many ic in general (op-amps, digital pots, transistors) to stay below < 130mA?

• Read specs again, It will give idle and operating current then add mA for any logic output loads with R. Dynamic current depends on rate of transitions (MHz) and Vcc Output loads add up. so Not so simple but you will get the hang of it. ARMs and Pics give power specs at end of spec. – Tony Stewart Sunnyskyguy EE75 Apr 9 '17 at 11:02
• @Tony Stewart Thanks. I try to read it but i can't understand. Does the "input current" refers to VDD or to Vout? Does the "clock" signal and the "Select chip" pin and the SDI pin consume current? Does this adds when several (ic) are connected? Does connecting the Vout pins to a Microphone input (for monitoring) drain current? I have made the circuit with 3 mcp4822, a couple of mcp6002 and some digital potentiometer ic and it worked but i get anxious. How to estimate the consumption of current? – John Am Apr 9 '17 at 11:39
• All loads add current.. best to add 100mV shunt series R and measure I . It changes with Vcc and loads and clock speed. learn to Control anxious. – Tony Stewart Sunnyskyguy EE75 Apr 9 '17 at 11:40
• If you're hoping there's a simple solution to your question, I'm afraid not - it's a pile of work. You have to go around all of your ICs, load resistors - everything - and work out what current they are drawing from supply and driving circuits. This is more difficult with active circuits but their datasheets may list dynamic current to add to static current, as TS has said. This is a 'best estimate' exercise on paper though there is software to do it for you. How accurate must the answer be? – TonyM Apr 9 '17 at 12:27
• Also consider a high-capacity digital buss: 32 lines, each 10pF, swinging 5 volts at 100MHz. What is the power? P = FCV^2 == 32 * 10^8Hz * 10^-11Farad 5*5 ==32*25 * 10^-3 = 0.6 watts. Your buss driver IC will also dissipate that power internally. What current? FC*V *32 = 0.12 amps. – analogsystemsrf Apr 9 '17 at 13:43