This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DLPDLCR4710EVM-G2: How I can change led current below 1423 ma!

Part Number: DLPDLCR4710EVM-G2
Other Parts Discussed in Thread: TEST, DLPA3005, DLP4710, DLPC3439, , DLPA3000, CSD17501Q5A, DLPDLCR3010EVM-G2, DLPDLCR2000EVM

Hi,

I want to decrease led current of dlp4710evm-g2 below of 1423ma down to 0 ma but when in dlp light crafter I was changed the led current below of 1423ma and click set button it did not set and when I click get button its value changed to 1423ma.

I test this in advanced mode but when changed value of Rgb led current and write 0 to all of them and click write button it did not set and when I click read button its value changed to 91.

Is there any solution?

  • Hello Jack,

    Welcome to DLP forum and thank you for your interest in DLP technology.

    Your observation is correct, this the lower limit for the LED current as per EVM design. You  can not operate at lower current. This is limitation is primarily due to following reason:

    1. The DLP4710EVM-G2 uses DLPA3005 for power management and illumination drive.  Please refer to the DLPA3005 datasheet (page 12, Electrical characteristic),  the minimum LED current is 1 amp.

    2. The LED drive circuit of the EVM is designed to drive LED current max upto 16 amp (green & blue) and 12 amp (reed). Often illumination system have a non linearity issue when they operate below 10% of  max capability.

    Because of the above reason,  system overt rights to minimum safe value when it changed to zero or low value.

    regards,

    Vivek

  • Hi,

    It is means that there is not any solution?

    Pls tell me a solution (any solution!)

  • Hello Jack,

    I am sorry that the EVM can not support your requirement.  The following are you options:

    1. design a custom board which meet your requirement. You  will need a new optical engine which has LED  to operate at such low current.

    2. Modify TI EVM for your requirement. It will require:

    • Modify LED drive circuit for low current. It will be a significant hardware change
    • Replace with LED which operate a low current; If you decide to use a smaller size LED (very likely) for it to operate in leaner range.  There may be brightness and color uniformity issue because Flyeye used in the optical engine is designed for larger size DMD.

    regards,

    Vivek

  • Hi,

    If refer to the DLPA3005 datasheet (page 12, Electrical characteristic),  the minimum LED current is 1 amp.

    How I can control Led current below of 1A?

    With what kind of changes I can do it?

  • Hi Jack,

    As Vivek had already mentioned the changes need to be made for the custom driver board and what are to be considered. SInce  you are not able to meet with the minimum requirements of supported DLPA3005 then you may have to design a custom LED driver board to be able to control it. 

    Could ypu please elaborate on why is it that you want to set the current levels to 0? 

    Regards,

    Akhil

  • Hi,

    I do not have a specific aim but it is a attractive challenge for me to do it!

     If I understand correctly، you said I must replace dlpa3005 and use another led driver. But I think dlp4710 and dlpc3439 and alpa3005 are the family and I can not chane any part of these family and they work in relation to each other. Is it true? So how I can chane a part of family pls explain it for me. 

    Can you send an example?

  • Hello Jack,

    The DLPC3439 product page (the controller on the DLPDLCR470EVM-G2) lists the compatible notes that the controller can also be used in configuration with the DLPA3000. This PMIC will drive less current (as low as 300 mA), but will not drive down to 0mA. Driving the current any lower is inadvisable and effectively impossible.

    Please do keep in mind that this will require a significant redesign and new firmware for to be supported by the DLPDLCR4710EVM-G2.

    Regards,

    Austin

  • Hi,

    Refer to the DLPA3000 datasheet (page 12, Electrical characteristic),  the minimum LED current is 0.3 amp but maximum LED current is 6A! And it is not good for me.

    If I have two resistor:

    1- 40m ohm

    2- 9m ohm + rds max csd17501q5a mosfet = 11.9 m ohm

    When mosfet is on I have 40m parallel with series of 9m and 2.9m (11.9m ohm) and I have 9.171 m ohm total resistor

    And when mosfet is off I have 40m ohm

    So In normal condition => sw is on so I have 1 to 16A

    And in low current condition => sw is off so I have 0.19A to 3.75A

    According to led current formula in page 44 of datasheet of dlpa3005 is it true? I can do it?

  • Hi Jack,

    Can you clarify what you are trying to achieve with a wide range of LED current ? There are a few things to keep in mind for the DLPA3005 and the LEDs you choose for the application.

    The DLPA3005 is intended for high power applications. So in typical application, one would want maximum current. In typical application, RLIM is intended to remain constant through operation. If RLIM is kept small, then it is possible to have wide range of LED current.

    It is also possible to drive the LED current to 0 during normal operation. There is an I2C command you can issue to controller, please see page 100 of the software programmer's guide here: https://www.ti.com/lit/ug/dlpu035/dlpu035.pdf

    Thank you,

    Chris

  • Hi,

    I checked this with light craft application and advance mode of that application.

    It can not do that and the value of those registers is not less than 91!

    On the other hand in the dlpa3005 datasheet in page 44 for led current value define a minimum value of 0x51 that equal with about 1A led current so how I can set it to below of 0x51?

    Do you mean that if I instruct dlpc3439 via i2c directly, for example via msp430 on the board, to set the value of this register to zero, the value will be applied?

    Assuming that the value of the current control register could not be less than 91, I intended to parallelize one branch of the series of one resistor and MOSFET with the main resistor so that the parallel product of the two branches were equal to the current 9 milliohms, but in The moment I want to reduce the current, by turning off the MOSFET, I practically increase the value of the rlim resistance to confuse dlpa3005 in the current measurement and feel that the current is greater than 1A and reduce the current to below 1A!

  • Hi Jack,

    To clarify my previous suggestion, the i2c command I wanted to show you was the RGB LED enable command (i2c op code 0x52). You can turn off the LED and you will get ~0 current. This i2c command is independent of the LED current DAC value (i2c op code 0x54 )that you command the controller.

    For your case, this is an interesting idea. I will need to speak with our hardware experts on the PMIC about your intended application. Please allow a few days for us to look into the querry and put together a response. 

    Thank you,

    Chris

  • Hi,

    What's up?

    Today I was 

    Today, through msp430, I set the dlpc3439 registers directly less than 0x5b to make sure that the restriction is not from software under Windows, which turned out to be directly from dlpc3439 itself and does not allow the value of current to be less than 0x5b.

    Is my idea (last post) workable and not a problem?

  • Hi Jack,

    Can you please confirm that the register you are referring to writing the value of 0x5b is the Write RGB LED Current (54h) register?

    Please see the below description in the DLPA3005 datasheet page 26 for the current limits dependency on Rlim resistor and the operating range i.e atleast 5% of LED_MAX is required.

    I recommend you to please wait for the confirmation from the hardware expects. Also please find my suggestion below  in case if your solution has been confirmed a feasible one from Hardware experts.

    Regarding the solution proposed by you to switch the mosfet and increase effective RLim to contol low currents. You should ensure that the current level register must be set properly according to the new effectove RLim value when switched. 

    Regards,

    Akhil

  • Hi,

    Regarding the 54h address, yes I confirm

     And as for the change in the value of the register after turning off the switch, you say exactly the true, I just do not know if it is possible to do these two things at the same time so that this change occurs without the step mode in the lighting setting?

  • Hello Jack,

    I am somewhat perplexed by your last question. What is the 'step mode' that you mention?

    As Akhil points out in his post, outside of the limitations to current on our PMICs, it is not recommended to output less than 5% of the maximum LED current. Frankly, we typically suggest allowing at least 10% clearance of the minimum to avoid any SNR issues.

    We will report back with our findings of further investigation.

    Regards,

    Austin

  • Hi Jack,

    Your suggested design is a feasible approach to expanding the range of the PMIC. However, there are a few caveats:

    1. Illumination block (on the PMIC) must be OFF prior to changing RLIM value. This means you will need to toggle PROJ_ON to get the illumination block stable. You cannot change RLIM while the projector is running.
    2. RLIM flat package resistor has multiple contacts on PCB, see the technical documentation on the tool page for whichever EVM you are using, you will see RLIM_K labelled a few different places. Keep in mind that the design around this is complex and we will offer very limited support outside of what we offer for our reference design.
    3. The MOSFET and RLIMs you choose must be able to handle high current. Whatever kind of specifications you may have for your product, be sure to source proper current handling capability.  

    Aside from this, the DLPC3439 will not allow you to reach 0x0000 with the RGB LED current command (54h). This is a limitation of the controller and cannot be changed.

    Thank you,

    Chris

  • Hi,

    Why can't I switch rlim while the LEDs are on? If I turn off the LED, then change the position of the resistor switch and then turn on the LED again, which results in a blink in the image, which is not interesting. 

  • Hi Jack,

    This is a limitation of the DLPA300x system. The illumination block must be switched off before RLIM is changed for reliable operation.

    Thank you,

    Chris

  • Hi,

    Please explain more about this issue, because in my opinion, changing the rlim is equivalent to changing the led current. With a sudden change in the current of the LEDs, the control circuit reacts quickly and re-stabilizes the current.

    So why is it difficult to change rlim while working? (The system does not open the circuit in any way, only one of the two parallel branches of the resistor enters or leaves the circuit with MOSFET)

  • Hi Jack,

    As stated in the previous response, this is a limitation of the DLPA300x system. For lower brightness applications, you may be interested in our DLPDLCR2000EVM or DLPDLCR3010EVM-G2. 

    Thank you,

    Chris