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SN65C1167E: Power consumption.

Kengo.Y
Guru 11255 points
Part Number: SN65C1167E

Tool/software:

Hi team,

I'd like to know how to calculate power consumption.
Could you pls advise what datasheet value to use?

BR,
Kengo.

  • +1
    TI__Guru 72981 points

    Kengo,

    Are you looking at power consumption to calculate heat dissipation for the device or for trying to figure out how to design your power rail max current draw?

    The majority of the power is going to come from the differential driver output. If we look at it from a DC standpoint then in a typical RS 422 set up you will have a 100 ohm termination resistor. So the power across the resistor will be VoD (3.7V) multiplied by the current (37mA = 3.7V/100ohms). So the power across the resistor is ~137mW. If we want to know the power across the differential drivers (minus the resistor) then it would be 37mA multiplied by Vcc-Vod (5V-3.7V=1.3V). So the power across the driver is ~48mW.

    So the total power across one of the device's driver is about 48mW. The total power across one output driver is 185mW. 

    There are two drivers in this device so you can 2x this number. For both drivers (without the resistor load) the driver output power is 96mW. For the total power (with the resistive load) the power output is 370mW. 

    You can add in some additional supply current power by just multipling the Icc by the Vcc. Using the larger number (9mA) multipled by Vcc (5V) you get 4.5mW

    If you want to estimate switching losses (AC) instead of DC then you can calculate that by: P_AC = C x Vcc^2 x f .......per driver.

    If your bus capacitance is 5nF (about 100 m of cable) and your data rate is 10Mbps (5MHz) then your AC losses from power is 625mW per driver. So the total power loss of the RS485 system for 2 drivers from AC losses would be 1.3W in this example.

    -Bobby