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MSP430 for driving 7 segment glass LCD

Chanh Nguyen1
Intellectual 290 points

Other Parts Discussed in Thread: MSP430FR4133, MSP-EXP430FR4133

I'm looking for a MSP430 series which is integrated LCD driver so as to drive a 7 segment LCD glass that has 4 commons and less than 35 segments. So which MSP430 series should I use for my project ?

Hop to get your support. Thanks !

  • 0
    TI__Guru* 84321 points

    Hi Chanh,

    We have a number of MSP430 device families with built-in segmented LCD drivers: MSP430F4xx, MSP430F6xx, MSP430FR6xx and MSP430FR4xx families all include built-in segmented LCD drivers, and all of them should support 4-mux mode that you require. You can search by sub-family using the product selection tool here: http://www.ti.com/lsds/ti/microcontrollers_16-bit_32-bit/msp/products.page

    If current consumption is important and depending on any other requirements for your application, you may want to check out the MSP430FR4133 - this device can keep the LCD on even down to LPM3.5 mode. There is a launchpad for this device available here: www.ti.com/tool/msp-exp430fr4133 if you'd like to try it out hands-on for evaluation. The other LCDs should have good current performance as well.

    To be honest, which of the MSPs that you choose is probably going to depend more on the other requirements for your application besides LCD, since we have so many different LCD device options and I think any of them should be able to support the basic small 4-mux LCD you described.

    Regards,

    Katie

    Regards,

    Katie

  • 0 in reply to Katie Pier
    Intellectual 290 points

    But in case a particular number of segment pins and common pins are sourcing/sinking, how I can estimate the increase in current consumption ?

    Because all information about current consumption in datasheet is in case output pins don't sink or source any current. I can't find any information related to this point. Hope you light me up. Thanks.

  • 0 in reply to Chanh Nguyen1
    TI__Guru* 84321 points

    Hi Chanh,

    LCD segment and COM pins will not be driving a constant high or low, but rather will constantly be toggling - this is because you cannot drive an LCD with just DC to turn segments on or you might damage the display, so toggling waveforms are used instead to provide AC signals. So the LCD controller is generating the waveforms you see in the user's guide that will be constantly toggling (even on the segments that are currently off) and come out to 0V DC - the RMS voltage applied to the segment will be what sets the segment on or off.

    The actual current that is going to get consumed when you use the LCD is going to depend a lot on the LCD display that you are driving - displays with more segments or larger digits will consume more current in general - each segment is sort of like a capacitor that you are charging and discharging constantly with the AC signals. The settings that you use when setting up your LCD module in the MSP430 will make a difference in current consumption too - whether you use the charge pump, internal vs external bias, bias resistors used (if external bias), etc.

    So unfortunately I can't give you a specific number saying that if your display has x segments on that it will consume x current. I can show you that some of our datasheets have a little information about current consumption of the LCD module (without the display - you'll have to get that part from the display manufacturer). In the MSP430FR4133 datasheet www.ti.com/lit/gpn/msp430fr4133 for example you can see in table 5.7 that we give an LPM3 number with the LCD on (the footnote explains the LCD settings used). As I mentioned this is ignoring the current of the display itself, only including the MSP430 with its LCD module on - you'll need to add the display current.

    I know this is not the best answer, but hopefully it will help. Best thing you can probably do is to try some prototyping and blue-wire up your display with an eval board. You could also try out the MSP-EXP430FR4133 launchpad which has an LCD display on-board.

    Regards,

    Katie

  • 0 in reply to Katie Pier
    Intellectual 290 points

    In fact, we only connect MSP430 and 7-segment based glass LCD through SEG and COM pins. There's no Vcc and Ground pins available here. So I think the display current you've mentioned is the current increasing on Vcc of MSP430. Is that right ? Because there's no DC part on SEG and COM pins while driving LCD, so I don't think there's current consumption there.

    Additionally, at present I wanna get an estimation about current consumption while driving LCD, so hope you can tell me the maximum current consumption rising up when running a particular 7-segment based glass LCD ?

  • 0 in reply to Chanh Nguyen1
    TI__Guru* 84321 points

    Hi Chanh Nguyen1,

    The LCD that you use is going to greatly impact the current consumption because the size of the LCD segments and the load of the LCD are going to greatly impact the current consumption as you drive it. As I mentioned in the last post, we can't really give you a spec for how much a particular LCD will increase the current consumption because it depends on the LCD glass you are using - you will need to try this yourself on a prototype. We can tell you what configurations of the LCD module will cause higher/lower current consumption but we can't give a number beyond what is already in the datasheet - this is because so much of it depends on the display and application - there are too many variables.

    Regards,

    Katie

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