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RM46L850: RM46L850 PIN2 can not driver LED for 6mA

HY yang
Expert 1980 points

Part Number: RM46L850

1:RM46L850PGET, the second pin (GIOA [0]/USB2.0VP/USB-FUNC.RXDPI) can not be controlled by software programming when using the open-leak output mode, that is, the indicator lights are often on; other output modes, such as push-pull output, are OK, please analyze the reasons.

2: At first, 40 boards use the output mode of opening and leaking. The indicator lights are programmable control. After aging for a period of time, two of the 40 boards appear the situation described above at 1 point.

3: The current of the test pin is 6mA.

4: The following is the schematic diagram:

  • 0
    TI__Mastermind 21425 points
    Hello,
    Are you connecting 2 red diodes in series? Could you tell me what is the forward voltage of 2 red LEDs that are used?

    Best regards,
    Miro
  • 0 in reply to Miro
    Expert 1980 points
    There is only one red diode in practical application. The forward voltage of the red diode is 1.8V-2.6V.
  • 0 in reply to HY yang
    TI__Mastermind 21425 points
    Hello,
    Output Buffer Drive Strength (sink/source) of GIOA pins is 2mA ( refer to Table 5-4 of device Datasheet ). You are using this pins out of recommended conditions. In your case '0' level on drain is not so important, but if the current is much bigger than 2mA this will lead to increasing of temperature and may damage the port.
    Did you measure the current is 6mA (if current is 6mA and LED is not damaged, then the LED must lit.) or you just calculate it?
    What I can suggest is to check whether the GIO is still working.


    Best regards,
    Miro
  • 0 in reply to Miro
    Prodigy 60 points

    Hi,

    If Output Buffer Drive Strength (sink/source) of GIOA pins is 2mA,why GIOA[0]( I_red=6mA) is normal,GIOA[1](I_green=3.73mA) is damaged?

    (1),we use GIOA[0](pin 2) ,open drain to control Red LED,test I_red=6mA;

        GIOA[1](pin 5) ,open drain to control Green LED,test I_green=3.73mA;

        GIOA[2](pin 9) ,open drain to control BlueLED,test I_blue=3mA;

        Now GIOA[0]and GIOA[2] are normal,but GIOA[1] is damaged，that is very trange.

    (2),Output Buffer Drive Strength (sink/source) of GIOA pins is 2mA,this is too small,normally MCU input current 10mA,why your MCU is only 2mA?

    (3),Your datasheet present,Input clamp current max is 10mA,and I_CCIO max is 10mA,why GIOA[1](I_green=3.73mA) is damaged?

    Thanks!

  • 0 in reply to Miro
    Prodigy 60 points

     Hi,

    Actually  only one red LED,only one grren LED,only one blue LED,but they are packaged in one device.

  • 0 in reply to yong zhu64
    TI__Mastermind 21425 points

    Hello,

    You should test whether pins are damaged. If you are measuring 6, 3mA and 3.73 mA then LEDs should lit!

    (1),we use GIOA[0](pin 2) ,open drain to control Red LED,test I_red=6mA;

       GIOA[1](pin 5) ,open drain to control Green LED,test I_green=3.73mA;

       GIOA[2](pin 9) ,open drain to control BlueLED,test I_blue=3mA;

       Now GIOA[0]and GIOA[2] are normal,but GIOA[1] is damaged，that is very trange.

    --> TI recommended conditions are stated in Datasheet. It is not recommended to use the device in where conditions exceeds recommended.

    (2),Output Buffer Drive Strength (sink/source) of GIOA pins is 2mA,this is too small,normally MCU input current 10mA,why your MCU is only 2mA?

    --> According to Datasheet Output Buffer Drive Strength for GIOA is 2mA. You should use buffer to drive load more than this.

    (3),Your datasheet present,Input clamp current max is 10mA,and I_CCIO max is 10mA,why GIOA[1](I_green=3.73mA) is damaged?

    --> Input clamp current is the current that flows through ESD protection diodes.

    --> Iccio max is maximum supply current that the device will consume from Vccio when there is no DC load.

    Best regards,

    Miro

  • 0 in reply to Miro
    Prodigy 60 points
    Hi，
    1,we have tested the pin GIOA[0](pin 2) ,open drain to control Red LED,test I_red=6mA, it is OK now ,not been damaged,software still can control it GIOA[1](pin 5) ,open drain to control Green LED,test I_green=3.73mA,it is NOK now,was damaged, software can not control it,it always keep low level.
    so we have no idea why 6mA pin still OK,but 3.7mA pin was damaged.
    2,what is meening of zero-dominant?
  • 0 in reply to yong zhu64
    TI__Mastermind 21425 points
    Hello,
    Zero dominant buffers:
    If two outputs are shorted together and one of them is driving a 1 while the other is driving a 0, then the result will be a 0 if the output buffers driving both the outputs are "zero-dominant" output buffers.

    Best regards,
    Miro