Part Number: TPS65120
I'm developping an electronic card with a 7 inches TFT touch screen (Winstar - WF70GTIAGDNT0#). This screen is controlled by a STM32F429IG microcontroller.
My screen needs several voltage to work :
- VCC voltage : 3V3 which is made by a buck converter
- VCOM voltage : 3V7 which is made by a TL431
- VGH voltage : 16V which is made by a TPS65120
- VGL voltage : -7V which is made by a TPS65120
- VMAIN voltage : 3V3 which made by a TPS65120
My issue comes from the TPS65120. If I didn't connect my screen on the board, all voltages work perfectly. If I connect the screen but without microcontroller, all voltages work perfectly. But with screen and microcontroller, all voltages are collapsing (VGH = 300mV; VGL = -250mV) as if the screen needs to much current, but without the microcontroller, it's not the case.
If you have any ideas, I'll be very happy.
Thank you in advance,
Could you please share some data for this?
Does the supply of the TPS65120 is also applied to any other rail?
In reply to Ilona:
Thank you for your quick answer.
Please, find in enclosed document my design :MACCS_HMI_REV1.pdf
The 3V3 which supplies the TPS65120 also supplies :
- the microcontroller
- A RS485 transceiver (MAX3430)
- A LCD backlight regulator (TPS61169)
- A PHY transceiver (DP83848), but not mounted at the moment.
This morning, I discovered a tool on TI's website (but now I cannot find it) where I have the choice of little/medium/large screen, and voltage regulator that gave me was the TPS65140 (more current 20mA on VGH et VGL).
In reply to fabricepeden:
Do you mean this tool:
How much current do you have on VMAIN when the output voltages drop? I wonder if the output current on Vmain with 25mA is not enough if your microcontroller is driving the screen. Could you check the current needed on the 3.3V? You could for example use a power supply to supply the 3.3V on the output of the TPS65120 when R28 is removed.
Please explain to me as well why your Vmain is below the VCOM voltage. I would expect the Vmain in the range of 2 times the VCOM voltage.
In reply to Brigitte:
Thank you for your answer.
Yes, for the tool, it's that one.
I just measure the current when I plug my screen. On Vmain, I measure 31mA, so that means that is too much for Vmain output.
As you said, I'll try with my "other" 3V3.
Concerning Vmain/Vcom, I just follow the specifications from Winstar (VCC = VMAIN) :
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