SN65DSI85Q1-EVM: How to use onboard LED backlight driver for tft lcd

ram adav

Prodigy 90 points

Part Number: SN65DSI85Q1-EVM
Other Parts Discussed in Thread: TPS61181A, DSI-TUNER

I am using SN65DSI85Q1-EVM to interface lvds tft lcd with my STM32F779i-EVAL board with dsi.

How can i use onboard LED backlight driver for lcd?

As per schematic there is no connection with backlight driver.

over 5 years ago

0 Ikechukwu Anyiam over 5 years ago

TI__Mastermind 35130 points

Hi ram,

It looks like there's a connection to the backlight driver via J2 and J5 of the EVM: www.ti.com/.../sllu221.pdf

Regards,
I.K.

0 ram adav over 5 years ago in reply to Ikechukwu Anyiam

Prodigy 90 points

Hi I.K.,

On J2 and J5 BL_PWR ( positive supply to backlight ) preset, but IFB1, IFB2 and IFB3 (negative supply for backlight) not connected to backlight driver IC(U10).

How to control backlight intensity?

Regards

Ram

0 Ikechukwu Anyiam over 5 years ago in reply to ram adav

TI__Mastermind 35130 points

Hi ram,

There's a note next to the backlight driver that states "DNI if external backlight driver used", so I imagine you just need to install R94, R95, R96, R97, R98, and R38 if you want to use the onboard driver. The DCTRL pin is used to control the intensity.

Regards,
I.K.

0 ram adav over 5 years ago in reply to Ikechukwu Anyiam

Prodigy 90 points

Hi I.K.

I have installed 0 ohm resistor for R99 and R98 for IFB1 and IFB2 as my lcd display have pin 31 and 32 as led negative pins.

As soon as I apply PWM with 500 hz frequency from my host controller which works on 3.3 V, backlight driver voltage falls to zero.

As per backlight driver ic datasheet only current will change.

Then why the backlight voltage goes to 0 V?

Regards

Ram

0 Ikechukwu Anyiam over 5 years ago in reply to ram adav

TI__Mastermind 35130 points

Hi ram,

Unfortunately I am not familiar with the TPS61181A, but I will go ahead and move this thread to the backlighting group where the device experts can help answer your questions.

Regards,
I.K.

0 Kenneth Du over 5 years ago in reply to Ikechukwu Anyiam

TI__Genius 14295 points

Hi, Ram,

Proper engineer has been assigned to take a look at this and will reply you soon.

Due to Chinese new year holidays, response maybe delayed.

Thanks for your understanding.

Regards,
Kenneth

0 Sean Zhou over 5 years ago in reply to ram adav

TI__Mastermind 22745 points

Hi Ram,
Sorry for the delay response, since you have observed the output voltage of backlight driver is zero, it must has came to falut state, have you connected the LED to those six channel (IFB1-6) and BL_PWR to your LCD panel? And have you checked whether the voltage on TP4 is right or not? And please make sure that you have pull up LED_BKLT_EN to high voltage state. If some falut occurs , Q1 will turn off the input power for backlight driver. So please check you have congfigured and connected the LED backlight driver correctly.
Regarsd
Sean

0 ram adav over 5 years ago in reply to Sean Zhou

Prodigy 90 points

Hi Sean,

On TP4 voltage is 5V as my supply to board is 5V.

I have not connected my lcd to board, because BL_PWR voltage is 13.5V.

My lcd backlight voltage requirement is 9 to 9.8 v (max), so I am worried about my lcd display as there is backlight voltage 13.5V.

How do I control backlight voltage?

Regards

Ram

0 Sean Zhou over 5 years ago in reply to ram adav

TI__Mastermind 22745 points

Hi Ram,
You need to connect the LCD panel, because it will detects open state and trigger OVP if you have not connected the LCD panel. The backlight voltage is adjusted automatically by the LED counts and current. So don't worry about the volage.
Regards
Sean

0 ram adav over 5 years ago in reply to Sean Zhou

Prodigy 90 points

Hi Sean,

I have connected LCD panel to J2 connector, Back-light is not turn on. Display not turn on.

I still not make any connections with microcontroller.

Still BL_PWR voltage is 13.5V.

I have read the datasheet of SN65DSI85Q1, in that there is possibility to generate lvds pattern without host microcontroller with just I2C.

What kind pattern will be generated?

How do I test my lcd with microcontroller?

Will my lcd show anything without host controller? Atleast backlight?

Here I have attached my lcd display datasheet. Please look and suggest me the solution.

1172.DT070BTFT-HB-PTS1-Displaytech-Spec-1384677.pdf

Regards
RAM

0 Sean Zhou over 5 years ago in reply to ram adav

TI__Mastermind 22745 points

Hi Ram,
I can't understand why BL_PWR is 13.5V, it means your boost has aleady switching? Have you soldered the R94 to R98? You can check whether there is pulse signal on BKLT_SW point? And for test with MCU, you need provide high signal(3.3V or 3V) on "LED_BKLT_EN" pin, and you need provide PWM signal on "DimmingCTRL" pin.
Regards
Sean

0 Ikechukwu Anyiam over 5 years ago in reply to ram adav

TI__Mastermind 35130 points

Hi Ram,

You can configure the DSI85 to display the test pattern without any host controller. Please use the DSI-Tuner to configure the registers, and reference this video:

You just need to check the test pattern box after filling in all the settings.

Please also note that although you don’t need a host controller to use the test pattern, you still need either a DSI CLK or an external reference clock.

Regards,

I.K.

0 ram adav over 5 years ago in reply to Sean Zhou

Prodigy 90 points

Hi Sean,

I have soldered the R94 to R99 (connected on IFB1 to IFB6).

I have seen pulse on BKLT_SW point. I have attached image of waveform.

I have given 3.3V signal (HIGH) on LED_BKLT_EN pin on J16 connector pin 3.

Also I have unistalled R63.

As soon as apply pwm (3.3V with frequency 500Hz and duty cycle 50%) from my I2C host controller, there is small sound and BL_PWR goes to 0V.

As I have done everything as you mentioned. where is the problem? Is this board support my lcd panel?

Atleast LCD Backlight should has to turn on.

Please Refer to my LCD Datasheet ( Attached) and revert me the proper solution.

5758.DT070BTFT-HB-PTS1-Displaytech-Spec-1384677.pdf

0 Sean Zhou over 5 years ago in reply to ram adav

TI__Mastermind 22745 points

Hi Mike,
I'm sorry that I don't have much commons on this problem, but I think you need to check your board and connection carefully.

0 ram adav over 5 years ago in reply to Sean Zhou

Prodigy 90 points

Hi Sean,

What should I do now to know the exact problem, so I can come with solution?

Can you provide me the display datasheet for which this board (SN65DSI85Q1-EVM) tested?

There is problem with backlight driver. For so long time I am in conversation I.K.. My Project is getting delayed. I am totally stuck now. I was selected this board to avoid mistakes. But there is no use of this board.

Please suggest solution as early as possible. Please my display datasheet and then decide this board will work with my lcd display or not.

regards
Ram

0 Sean Zhou over 5 years ago in reply to ram adav

TI__Mastermind 22745 points

I'm sorry that I'm not the writter of this document, I can help to communicate with the writor.
Regards
Sean

0 Sean Zhou over 5 years ago in reply to Ikechukwu Anyiam

TI__Mastermind 22745 points

Hi I.K,
Can you provide the display datasheet for which this board (SN65DSI85Q1-EVM) tested to this engineer?
Regards
Sean

0 Ikechukwu Anyiam over 5 years ago in reply to Sean Zhou

TI__Mastermind 35130 points

Sure, this is the display used with the EVM: www.beyondinfinite.com/.../LP101WSA-TLN1.pdf

Regards,
I.K.

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SN65DSI85Q1-EVM: How to use onboard LED backlight driver for tft lcd