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MSP430F67471A: Question about LCD power consumption

Part Number: MSP430F67471A

Hello.

I have a question.

When connecting the LCD panel with the same register setting as ILPM 3 LCD, CP described in datasheet page 30, what should be considered in addition to the current consumption shown below?

· ILPM 3 LCD, CP
· Maximum value of current consumption described in LCD panel data sheet

Regards,

  • Hi Keirs,

    In addition to the current values, I suggest that you take a look at the following document: www.ti.com/lit/an/slaa654a/slaa654a.pdf

    This covers many of the considerations that you should take into account when connecting the LCD to the MSP430 and choosing the correct register settings.

    Regards,
    Nathan

  • Hi Nathan,

    Thank you for your reply.
    I read it.

    1.Since ICC, Peak, and CP described in Section 4.9 of the document taught are not included in the I LPM 3 LCD, CP described in the data sheet, do you need to add to the current consumption calculation?

    2.In that case, how much current consumption should be supposed to be increased?
    I do not know how to assume the charge pump duty cycle.

    3.Is there anything else that greatly affects current consumption?

    Regards,
  • Hi Nathan,

    Do you have any update about my questions?
    Regards,
  • Hi Keirs,

    1. The value in the datasheet (ILPM 3 LCD, CP) is the typical value. The other document is simply stating that ICC, Peak, CP is the maximum value that this current can be.
    2. To determine how much the average current will decrease, you will need to use the time to charge C_LCD and the peak current, as stated in the other document. Please find these values in table 5-38 of the datasheet.
    3. There should not be. As stated in the other document, when charge pump is not at its peak current, the module will be in its lower current state.

    Regards,

    Nathan

  • Hi Nathan,

    the module will be in its lower current state.
    ->When it is "lower current state", does the current consumption be ILPM 3 LCD, CP(when charge pump is enabled)? 

    When measuring the consumption current of Vcc under the following conditions, it was 17 uA. The maximum consumption current consumed by the connected LCD panel is 4 uA. I assumed supply cutrrent is :total of the ILPM 3 LCD, CP(3.2uA) + LCD panel supply current(4uA), but what other points do you think is consuming current consumption?

    ・All inputs are tied to 0 V or to VCC
    ・The currents are defined with crystal capacity of a load capacitance of 12.5 pF
    ・RTC is disabled
    ・ACLK = low frequency crystal operation (XTS = 0, XT 1 DRIVE x = 0)
    ・CPUOFF = 1, SCG 0 = 1, SCG 1 = 1, OSCOFF = 0 (LPM 3); fACLK = 32768 Hz, fMCLK = fSMCLK = fDCO = 0 MHz
    ・SVS is disabled
    ・LCDMx = 10, LCDREXT = 0, LCDEXTBIAS = 0 (internal biasing), VLCDREFx = 3.02 V, Flcd = 384 Hz

    Regards,

  • Hi Keirs,

    Yes, the lower current state is when the device is in LPM3. Did you take the peak current into account (as discussed above)?

    Are these measurements taken while writing to the LCD?

    Regards,
    Nathan
  • Hi NathanS,

    Thank you for your reply.

    Yes, the lower current state is when the device is in LPM3.

    Did you take the peak current into account (as discussed above)?

    -> No. Is it correct by understanding as shown in the figure below? Also, could you tell me how to calculate the marked part?

     How does the ICP, Load of data sheet table 5-38 affect the following figure?

    Are these measurements taken while writing to the LCD?

    ->Yes, writing to the LCD as follows.

    LCDM1 0x77
    LCDM2 0x77
    LCDM3 0x77
    LCDM4 0x77 
    LCDM5 0x77 
    LCDM6 0x77 
    LCDM7 0x77
    LCDM8 0x77 
    LCDM9 0x07 

    LCDM10~LCDM40 =0x00

    LCD Blinking Memory is All 0.

    Regards,

  • Hi Keirs,

    Your understanding based on the diagram is correct. I do not see the time that the charge pump is off in the datasheet or user's guide, so I will try to find that information. As for the charge pump average current, that is what you will have to calculate using the LPM current and the peak current.

    Either way, though, it should be much less than the 17 uA that you said you were measuring. Please keep in mind that the current that you are calculating is only what is being consumed by the MSP430. The LCD itself will be drawing current as well, and you will need to find out how much current that is drawing.

    Regards,
    Nathan
  • Hi Nathean,

    Thank you for your reply.

    I do not see the time that the charge pump is off in the datasheet or user's guide, so I will try to find that information. 

    ->I am waiting for new information about your investigation.

    Please keep in mind that the current that you are calculating is only what is being consumed by the MSP430. The LCD itself will be drawing current as well, and you will need to find out how much current that is drawing.

    ->By connecting the LCD and the MSP 430, what additional current can be considered in addition to the current consumption measured by each?

    Do you have any updates on my question below?

    >How does the ICP, Load of data sheet table 5-38 affect the following figure?

    Regards,

  • Hi Nathan,

    I am sorry to ask you many times.
    Do you have any updates about my questions?

    Regards,
  • Hi Keirs,

    I will get back to you about the time that the charge pump is off when I find that out. I have asked the Systems team and am waiting for a response.

    Connecting the LCD to the MSP430 will not necessarily draw extra current, but it is important to keep in mind that many other factors will affect your current such as the LCD glass and the number of segments that you are driving.

    ICP, Load will not affect the figure or your calculations.

    Regards,
    Nathan
  • Hi Nathan,

    Thank you for your reply.

    I understand.

    I'm waiting for your contact.

    Connecting the LCD to the MSP430 will not necessarily draw extra current, but it is important to keep in mind that many other factors will affect your current such as the LCD glass and the number of segments that you are driving.


    ->If there are other possible factors, can you tell me specifically?

       What can I do to reduce power consumption when handling LCD with MSP 430?

    Regards,

  • Hi Keirs,

    The main factors will be the LCD that you are using and the number of segment pins that you are using. There are many different LCDs out there and the number of segment pins, as well as other possible factors, can change depending on your implementation. There are not numbers provided for these changing factors because of this. I would suggest that you prototype your setup with the MSP430 and the LCD and measure the current to get a more accurate assessment.

    As for additional ways to reduce power consumption, I would suggest that you look at the rest of the slaa654a document that I linked to. Section 4.9 specifically lists some ways to reduce your power consumption in addition to using a low duty cycle for the charge pump.

    Please see the following threads for some similar discussions:
    e2e.ti.com/.../382207
    e2e.ti.com/.../280974
    e2e.ti.com/.../564452

    Regards,
    Nathan
  • Hi Keirs,

    I apologize for the delay, but I have heard back from our LCD experts. The charge pump is adaptive. That means depending on the load (external capacitance, type of LCD, frame rate), the CP turns on or off. That is why we don't specify the CP off time in the datasheet. Because of this, I again suggest that you prototype what you are doing and measure it. There are too many variables here to give you an exact number, so you will need to take measurements based on your exact configuration and choice of components.

    Regards,
    Nathan
  • Hi Nathan,

    Thank you so much for checking out.

    I understand.

    I will try to examine the current consumption based on the measurement and the advice I gave you.

    Regards,

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