MSP430 IO Pin Output Voltage too low to supply TLV2780 OP Amplifier

Dear Friends:

  I followed the SLAA335 "Implementing A Smoke Detector With The MSP430F2012" use one IO pin P1.3 to power TLV2780.

   I found that IO output voltage only 0.9V, but it is 3.3V if I disconnect IO Pin P1.3 from TLV2780.

  I use MSP430G2232 instead of MSP430F2012.

 Who can kindly tell me what the problem is ?

and how to soult the problem ?

Thanks !

Marshall Wu 

 

  • This is very low power amplifier, every msp430 shall be able to supply it from single pin. Perhaps amplifier output is connected to pin which is improperly configured as output and set to logical 0.

  • In reply to Ilmars:

    Dear llmars:

      Thanks for your prompt response.

      TLV2780 output is connect to P1.0( as ADC10 input) and P1.3 for TLV2780 power.

      I config P1DIR = 0x5a, (P1.0 input, P1.3 output)

                 P1OUT=0xaf,(P1.0 & P1.3 are high)

                 P1REN=0xee,(P1.3 with pull resistor, P1.0 without pull resistor)

                 P1SEL2,P1SEL = (0x00,0x00), (0x00,x01) or (0x01,0x010) have no difference.

                 ADC10AE0= 0x01;(enable P1.0 as analog input)

                 P1.3 output ~=0.83V,

                 When I connect Vcc=3.3V to TLV2780 VDD then every thing seems normal.(OK)

                Would you please check the above configuration to see what's wrong ?

                Thanks !

                Marshall Wu 

  • In reply to CHEN YOUNG WU:

    CHEN YOUNG WU
     When I connect Vcc=3.3V to TLV2780 VDD then every thing seems normal.(OK)

    Still you need to check against amp output "short". Disconnect amp output from uC and then try to power it.

  • In reply to Ilmars:

    I disconnected the TLV2780 output from uC P1.0

    Checked that P1.3(for OP power) is still 0.83V when P1.3 is output high(P1OUT = 0x08.

    why ?  the OP amplifier circuit is complete same as SLAA335 OP amplifier circuit.

    Thanks !

  • In reply to CHEN YOUNG WU:

    CHEN YOUNG WU
    why ?

    Out of ideas. Particular (single) opamp consumes 0.8mA, single I/O pin is more than enough to power it.

    Do you use amp having 1 channel? Maybe you somehow blew opamp or blew output pin P1.3? Forgot to (properly) connect VCC to msp430?  

    Check current draw of the circuit when amp is powered directly from VCC.

    Check what's happening with VCC rail, other output pins having logical 1 - while you power amp from P1.3.

    Open your mind and check whole circuit including pinouts of both ICs, resistor values.

  • In reply to Ilmars:

    TLV2780 is a single channel OP amp. it consuming 560uA when direct power by VCC.

    MSP430 VCC and VSS(GND) checked.

    checked, when P1.3 power OP the other P1.4 output is 3.3V

    I config P1.3 as a digital IO output function with pull up/down.

    When OP power by VCC, the ADC10 and OP amp are both function correctly.

    are there any other configuration I've missed ?

    Marshall  

  • In reply to CHEN YOUNG WU:

    CHEN YOUNG WU
    are there any other configuration I've missed ?

    Dunno. Can't check your circuit from here, can't check your source code either (because you don't show it all).

    BTW I never use pull-ups for outputs - can't say it changes something or not. Try to disable it.

    Try to power amp from another pin configured as output, without pull-up resistor and without according P1SEL bits set.

  • In reply to CHEN YOUNG WU:

    Ok, so you've got a pullup resistor (because pin is driven high) and you've connected a load to it. What you get is something like this:

    If you replace the opamp with a resistor to model the load, you get a Voltage divider. No wonder you only get 0.83V on the device because the rest has already dropped on the pullup resistor. Disable the pull resistor and it will probably be fine or perhaps provide Voltage to the opamp through a mosfet which you'd then drive from P1.3-- that would probably be a little neater (personal taste though).

  • In reply to Arturs Elksnis:

    Arturs Elksnis
    Ok, so you've got a pullup resistor (because pin is driven high) and you've connected a load to it.

    No, he did not. F2012 pin schematics says that pull-up resistor is enabled only for input direction.

  • In reply to Ilmars:

    Ilmars,
           In the first post in this thread Wong Chen Young Wu says this: 

    CHEN YOUNG WU
     I use MSP430G2232 instead of MSP430F2012
     

    So forget the F2012. Now in the document "MSP430x2xx Family User's Guide" (latest link: http://www.ti.com/lit/ug/slau144j/slau144j.pdf), page 328 and 329:

    Port schematics of G2232 for P1.3 seem to correspond to that too.