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MAX3221: low power mode

Cooper Zhang1
Expert 2190 points
Part Number: MAX3221
Other Parts Discussed in Thread: MAX3227, TRS3227

Dear，

Merry Christmas~

as below,  Pin12  connect to GND and  pin 16 connect to 3.3V , Can it be in low power mode ? 

  • 0
    Guru 317280 points

    As shown in table 8-1, with these connections, the driver is in automatic power down mode when the RIN voltage is not valid (i.e., when the bus is disconnected, or when the driver at the other end is disabled).

  • 0
    TI__Mastermind 48108 points

    Hi Cooper,

    Here is the table that Clemens is talking about:

    Automatic power down mode is enabled when FORCEON = LOW, and /FORCEOFF = HIGH. Valid RS232 voltage level will result in normal operation on DOUT. Non-valid RS232 voltage level results in device being powered off by automatic power down feature. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    TI__Intellectual 2675 points

    Hi Tyler,

    This customer follow the automatic power down configuration as shown above. However, when connect a RS232 cable to PC, the current consumption is increased from 1uA to 4mA which is very high for system. We monitor the /INVALID which keep at H logic. We assume the device should still keep in power down mode which could consume less current.  What can we do to reduce the current consumption for the cable connected but standby situation? Thanks a lot.

    Best Regards,

    Tess Chen

  • 0 in reply to Tess Chen
    Guru 317280 points

    The MAX3221 stays up because the PC generates a valid RS-232 level.

    The MAX3227/TRS3227 automatically powers down when the RS-232 bus has a valid voltage but stays idle for 30 s.

  • 0 in reply to Tess Chen
    TI__Mastermind 48108 points

    Tess Chen,

    Thank you for the questions.

    For RS232, there is a indeterminate region between -3V to +3V. Within this range, data in this range cannot be interpreted by the standardized receiver. The idle state for RS232 is to output low voltage = ~-12V, which is probably the voltage level coming from the PC. 

    Invalid pin is always HIGH (H) when input RIN = L, or RIN = H. Pins FORCEON, /FORCEOFF, and /EN are irrelevant to the output state of /INVALID, which is why this pin keeps HIGH. We can see this in logic table from the datasheet below.

    Clemens mentioned p2p compatible devices: MAX3227/TRS3227 that could replace MAX3221 if low-power mode is desired when RS232 signal lines are left idle. MAX3227/TRS3227 enters low power state (1uA) after max 60 seconds of inactivity. 

    Regards,

    Tyler