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Replace LCD A board of EVM AM3358

GeoD
Intellectual 325 points
Other Parts Discussed in Thread: AM3358, TPS63010, TPS61081, SN74AVC32T245

Hello,

I have an EVM with the AM3358 and want to disconnect the EVM LCD A board and make my own LCD pcb for connection to a new display and touchscreen (24-bit paraller RGB, white LED for backlight etc).

1) Can you tell me the current that each of the input supplies to the LCD board supports (V5_0D, VEXPD, V3_3D_SRC, J1, J2, J3 connectors)?

2) What is the sequence of the above supplies that the LCD board sees? which one comes first, second etc?

Thank you,

Yu-Li

  • 0
    TI__Intellectual 2150 points

    VEXPD should be used for the main input to your power supplies on your LCD board since this comes straight from the main +5DC input power supply on the base board (after the power switch) and your efficiency will not be diminished by running through multiple regulators.

    V5_0D is generated from a TPS63010 and is used primarily for USB.

    V3_3D_SRC comes from a TPS79501 on the daughterboard and powers most 3.3V items on the EVM.

    The order of power sequence of these is VEXPD first, V3_3D_SRC second, and then V5_0D.

  • 0
    TI__Guru**** 393215 points
    Hi Yu-Li,
     
    VEXPD is actually VBAT from the Baseboard - ramps up first. Supported current is input current for EVM minus Baseboard and Daugtherboard consumption.
    V1_8D and V3_3D are sourced from LDO's U52 and U53 on the GP Daugtherboard, enabled from PMIC_PWR_EN (AM335X pin) - ramp up second. Both LDO's are 500mA.
    V5_0D is sourced from Buck-Boost U24 on the GP Baseboard, enabled from V3_3D - ramps up last. Supported current is 800mA in boost mode, 1200mA in buck mode.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Intellectual 325 points

    Hi again,

    Thank you for your answers. I have some further questions.

    1) Can you tell me please what is the backlight power that the LCD EVM supports? (U5 circuitry). I'm trying to understand the circuitry and compare it with my backlight requirements.

    2) This actually worries me as I am using a lot of the LCD schematics for my new display card. I noticed a discrepancy between the TI schematics and LCD EVM board (the actual PCB). The LCD board seems to have fitted a Q2 device (could be a transistor or FET?) and some additional resistors (R78, R78, R77, R37 (NOT FITTED and this is not the R37 that is on the TI LCD schematics). I have check the LCD schematics that are available today from TI website, version is REV1.1A and the components I have mentioned above are not included. Can you advise please?

    Thank you,

    Yu-Li

  • 0 in reply to GeoD
    TI__Intellectual 2150 points

    See the rev. 1.3A LCD board schematic (and other GP EVM board technical files) at: http://processors.wiki.ti.com/index.php/AM335x_General_Purpose_EVM_Board_Design_Files.

    1) The TPS61081 is being used in constant current mode to power the white LED's in the backlight.  See the datasheet for the TPS61081 for further details.  You can also get more information by posting a forum message to the TPS61081 team.

  • 0 in reply to ddomke
    Intellectual 325 points

    Hello,

    I have a question regarding the EVM AM335X LCD schematics. Assuming you loose the VDD_LCD power on U4 (SN74AVC32T245). Since the OE and DIR pins are controlled by the VCCA which is the VDD_LCD how do you ensure the data is not travelled to the opposite direction (A to B and not B to A)? how someone can handle this situation?

    thanks,

    Yu-Li

  • 0 in reply to GeoD
    TI__Guru**** 393215 points
    Hi Yu-Li,
     
    The DIR pins on U4 are tied to GND, meaning direction is always B to A.
     
    Best Regards
    Biser