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Backlight LED Driver

Rajesh Kumar72
Intellectual 500 points
Other Parts Discussed in Thread: TPS61169, LM36923H, LP8556

Hello Support team,

Currently we are looking for a suitable Backlight LED driver to be designed for our display application.

Requirement specs are as below:

For DAY mode, operating voltage is 28.5V +/- 0.5V and operating current is 50mA and

For NIGHT mode, operating voltage is 26.5V +/- 0.5V and operating current is 5mA

Backlight LED circuit consists of 2 series and 5 parallel LEDs and we have been provided only two pin connector to drive these LEDs.

Input voltage: 12V +/-10%

Dimming method: PWM preferred

Could you please suggest few efficient and economical LED drivers to meet the above requirements.

Thanks & Regards,

Rajesh Kumar

  • 0
    TI__Genius 11836 points

    Hi Rajesh,

    What's your application? Automotive or industrial?

  • 0 in reply to Charles-Chen
    Intellectual 500 points

    Hi Charles,

    Currently we are developing prototypes for industrial application, operating temp range is -20deg C to 70degC.

    Regards,

    Rajesh 

  • 0 in reply to Rajesh Kumar72
    TI__Genius 11836 points

    Hi Rajesh,

    I loop in Sean to support on this request.

  • 0
    TI__Genius 13001 points

    Hi Rajesh,

    It seems that single channel LED driver is proper for you. 

    Pls. rfer to tps61169, and separate the power supply and VIN, 12V connects with VBAT and power below 5.5V connects with VIN.

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Intellectual 500 points

    Hi Robin,

    Looking at TPS61169, looks fine for driving 50mA current by selecting 4.08 ohm current sense resistor. But to reduce the current to say, 5mA, sense resistor values is 0.408 ohm. Feedback value accuracy is roughly +/-8%, so current accuracy will be also +/-8%. With TPS61169, can we regulate 5mA current?

    I have also gone through couple of other options available from TI, such as LM36923H Highly Efficient Triple-String White LED Driver. With this regard, I have couple of questions:

    1. Through I2C, we can selectively set the sinking current 2.5mA and 25mA respectively for night and day mode. By paralleling Led1 and Led2 output we can achieve the desired current od 5mA and 50mA. Do you see any issues with paralleling these two led outputs?

    2. Only difference here is, I have to down-convert 12V to 5V to drive this boost converter. We we select the inductor for maximum required current of 50mA, how does current regulation will be affected at lighter load, 5mA? Hopefully stated current accuracy of –3% 0.1% 3% will be met, please comment.

    3. This device supports 4 different programmable OVP voltage thresholds. With respect to our application, max operating voltage is 29V, so which setting will be optimal - 31V or 38V? To decide on that which all LED parameters we shall know?

    Is it possible to have offline circuit design review? If yes, please share your email id, we will provide you the circuit for review.

    Thanks & Regards,

    Rajesh

  • 0 in reply to Rajesh Kumar72
    TI__Genius 13001 points

    Hi Rajesh,

    You can set the sense resistor with 50mA, and decrease the PWM duty to 10% to get 5mA output. Yes, the current accuracy is related with the reference voltage accuracy.

    For LM36923H,

    1) This device supports paralleling channels.

    2) It can also be kept below 3%.

    3) It depends on LED forward voltage variation along with various current. If 31V is satisfied, 31V is safer.

    You can send me your circuit. I will contact with you later.

  • 0 in reply to Yuting Shao
    Intellectual 500 points

    Hi Robin,

    Thanks for the clarifications.

    We have got the following requirement specifications from the backlight LED module manufacturers.

    Mode - Day / Night Parameters Values, typical
    Day mode  Operating voltage 28.5V
    Day mode operating current 50mA
    Day mode Brightness 1000 nits
    Night mode operating voltage 26.5V
    Night mode operating current 5mA
    Night mode Brightness 30 nits

    With respect to above requirement specs, we want to set 28.5V & 50mA operating conditions to achieve day mode brightness and similarly to achieve night mode brightness, operating conditions to be set as 26.5V & 5mA.

    Do you have any LED driver which can meet above specs?

    We understand that required level of brightness can be achieved by changing the forward current of the LED module, however OEM keeps on emphasizing on regulating voltage as well as current both to meet the above brightness requirements. Have you come across such unique feature of driving conditions?

    Do you have any LED driver IC with which we shall be able to program the boost outout voltage as well as control the current either through hardware configuration or software configuration?

    Please let us know what other parameters or specs we should get from backlight LED manufacturers to select a suitable backlight LED driver?

    Regards,

    Rajesh

  • 0 in reply to Rajesh Kumar72
    TI__Genius 13001 points

    Hi Rajesh,

    There are a few devices which can control output voltage and current at the same time.

    LP8556, LP8866 are devices that has adaptive voltage feature, and the max. and min. adaptive voltage can be set by yourself.

    BR,

    Robin