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MAX3221-EP Power Consumption

Ryan K
Prodigy 10 points
Other Parts Discussed in Thread: MAX3221-EP

I am trying to complete a power consumption estimate for a design and the datasheet for the MAX3221-EP has me confused.

At the bottom of page 3 in the datasheet the supply current is given for a number of different scenarios.  I don't plan to use the auto-powerdown feature so the top most supply current rating is the most applicable to my situation.  This value is listed as 2mA max, however, one of the criteria is "no load."  This chip will be driving another device which I do not have detailed design information for other than that the interface is EIA-232 compliant.

My questions are:

  • Is this max current rating still a reasonable estimate for when this chip is loaded down with another EIA-232 device over a short cable?
  • Does the provided current value assume the maximum possible datarate (250kbps)?
Any advice would be greatly appreciated!
  • 0
    TI__Guru**** 158716 points

    Hello Ryan,

    The receivers won't add much to the power consumption so I’ll focus on the drivers.

    For each driver the DC current is: I=5.4V/RL  (RL is load of remote RS232 receiver)

    For each driver the switching current is: I=Fo*CL*10.8V^2/5.4V this is same as I=Fo*CL*21.6V 
    Fo is the driver frequency which is not the same as bits per second.  CL is capacitive load on the driver line. 10.8V is the peak to peak voltage and 5.4V is the charge pump voltage.

    Add all the currents calculated above. This is the total current required of the charge pump.  Now ICC can be calculated.  Icc=0.3mA+2.3*I[total]  The 0.3mA is the typical static ICC, the 2.3 is the measured charge pump efficiency factor.  If supply power is needed, multiply ICC by VCC.

    This will provide a good estimation of active power consumption.

    Regards,
    Ron Michallick