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Charge pump to power external LCD

Trilogis
Prodigy 170 points
Other Parts Discussed in Thread: MSP430F4270


I have a design with an MSP430F4270, powered with a 3V lithium battery.
During product lifetime, the battery voltage changes from 3.2V down to 2.5V.

I also have an external chip on glass LCD display, driven by a classical 3 wires digital interface.

To ensure a good contrast on the LCD segments, I would like to power the external LCD through the MSP's LCD charge pump, VLCD is available through the LCDCAP pad (with 4.7uF cap). The VLCD voltage can be regulated at 3.02V.

The internal MSP's LCD driver is not used at all.

This works fine when the system starts, but after few seconds (typ 10sec) the VLCD drops as if the charge pump would be disabled...

Nothing is changed at register level, clocks are not stopped.

Does anyone know what is happening ?

  • 0
    TI__Guru 64610 points

    First thing I would suggest as a quick test is to use one of the code examples, if you haven't already, to test the VLCD output to ensure stability.

    These examples can be found on the MSP430F4270 Product Folder in the Tools & Software section in the slac077c.zip file.
    http://focus.ti.com/docs/prod/folders/print/msp430f4270.html

    http://focus.ti.com/docs/prod/folders/print/msp430f4270.html#toolssoftware

    As a quick test, try the msp430x42x0_lcda_05.c.  This code example disables the watchdog and sets up the VLCD.

     

    Is your application otherwise still functional?

    Using the MSP430x4xx Family User's Guide (SLAU056) as a guide, Figure 25-1 on page 695 shows the various register bit fields and signals affecting the operation of the charge pump.
    These would be VLCDREFx, VLCDx, LCDCPEN and the output of the ACLK divider LCDFREQx.  I would suggest searching for areas of your application that may be affecting these bit fields.

  • 0
    TI__Expert 5365 points

    Hi Trilogis,

    In addition to what Brandon said, I would like to know what mode your LCD is configured to. I am assuming since you are not using the LCD driver, you probably are in Static Mode. However, I will repeat your exercise with one of the MUX mode selected and see the results. Do report what you see :)

    Best regards

    Kripa

     

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