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TLV803Z used as a 200ms LED blinker

Other Parts Discussed in Thread: TLV803

Is there a reason that the TLV803Z reset IC cannot be used as a 200msec LED blinker.  My application is to show that a battery powered MSP430 application is running using an output port that switches at 1 Hz or 1 second 3.3v, 1 second 0v so that an LED would blink for 200ms every 2 seconds. The LED is connected through a resistor to the Reset output and the VDD input is connected to a MSP430 output.

  • Hi Larry,

    If I am understanding your intended application correctly, it could be possible. Please keep in mind that you will need to limit the current so you do not exceed the current rating of the SVS. Also since Vdd is also the sense pin for the TLV803 family, unless your pullup voltage is also Vdd, you will transition through periods where /RESET is in an undefined state.

    Very Respectfully,
    Ryan
  • Hello Ryan,

    Thanks for your help.

    For my design the reset output connects to  a resistor and then the cathode of an LED, anode is connected to 3.3v (current is limited to less than 2ma).

    The VDD pin is connected to a MSP430 output port which is either 0v or 3.3v (source current max of 6ma at 3.3v).  My assumption is that the TLV803Z internal MOSFET is OK being connected through the resistor and LED to 3.3v for long periods with the VDD pin in the 0v state.

    Is there an issue with protection diodes from the Reset output providing current flow through the VDD pin when it is connected to an MSP430 port providing logic 0 (0v)?  My issue is to make sure the LED is OFF and there is no wasted power.

    If this is the case then the MSP430 Port would need to be set to be an input pin for the LED OFF case with input pull down resistor (~35K). To blink the LED the same MSP430 port would be set to an output pin logic 1 (3.3v) with the pull down resistor disconnected to save power.

  • Hi Larry,

    Your application should work as you describe. The LED would be off for 1.8s and blink on for 200ms. There will not be any damage to the SVS as you would not violate any conditions.

    When I made my statement about the undefined region I was thinking of a more traditional, slow moving rail. As your application will have fast transitions on Vdd you will pass through this undefined region quick enoguh that the region is neglibilble. I apologize for the confusion.

    Very Respectfully,
    Ryan