• State Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 1779 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM3435 / unused pin, control freq

Junya Kato
Expert 1635 points
Other Parts Discussed in Thread: LM3435

Hello Team,


1) Please tell us about the treatment of unused pins.

- SVDD(11): need to insert the any voltage?

- SDATA(12)

- SCLK(13)

- FAULT(27): connect to GND via a resistor?

- EN(28): floating OK?


2) I want to control the GCTRL/BCTRL/RCTRL by the signal of 42kHz.
Is it all right?
Do you have a frequency spec?


Best regards,
Kato

  • 0
    Expert 1635 points
    Hello Team,

    Your early reply will be greatly appreciated.

    Best regards,
    Kato
  • 0 in reply to Junya Kato
    TI__Expert 3920 points

    Dear Kato-san,

    SVDD should be connected to a 5 V for proper I2C operation.

    If your system does not need I2C, you still need to have SVDD connect to 5 V.

    Please connect SDATA and SCLK to SVDD through resistor, 10k-ohm would be fine.

    FAULT is an output pin, do not connect to ground or VIN or other place. If you do not need fault indication, just leave it open.

    EN has internal pull-up, so it should be ok for floating.

    We did not try any frequencies that was higher than 2-kHz on GCTRL/BCTRL/RCTRL. So it is not guaranteed to work at 42kHz.

    I hope the above answers your question.

    Thank you very much!

  • 0 in reply to Issac Hsu
    Expert 1635 points
    Hello Issac-san,


    Thank you for your reply.
    We have a question with additional.


    >If your system does not need I2C, you still need to have SVDD connect to 5 V.
    We are input the battery/USB voltage(2.9-4.2V / 5V) to Vin.
    Is it OK to connect SVDD to Vin(2.9-4.2V / 5V)?


    >We did not try any frequencies that was higher than 2-kHz on GCTRL/BCTRL/RCTRL.
    >So it is not guaranteed to work at 42kHz.
    Would it be possible to present frequency characteristics of GCTRL/BCTRL/RCTRL?


    Best regards,
    Kato
  • 0 in reply to Junya Kato
    TI__Expert 3920 points
    Hi Kato-san,

    Yes, it is ok to connect SVDD to VIN (as long as it is above 2.5 V).

    LM3435 is a sequential mode device, each color can turn on one-by-one only. There is no overlapping mode supported.
    As you can see from the datasheet, we have a typical 35 us delay during color transition.
    Combining with the duty cycle consideration, these are the limiting factors for the frequency of use with CTRL signals.

    Thanks!
  • 0 in reply to Issac Hsu
    Expert 1635 points

    Hello Issac-san,


    1) Can the attached waveform be input to the G/B/L CTRL pin of the LM3435?

    2) Will delay time (default: 35us) occur between ON pulses under control of the same color?


    Best regards,
    Kato

  • 0 in reply to Junya Kato
    Expert 1635 points
    Information is needed immediately to complete the circuit design.
    The limit is November 14th.
  • 0 in reply to Junya Kato
    TI__Expert 3920 points
    Hi Kato-san,

    We did not tested such pattern before and we don't know about the feasibility of such configuration with LM3435.
    As far as I know, the 35us delay does not implemented on the same color.

    Thank you!
  • 0 in reply to Issac Hsu
    Expert 1635 points

    Hello Issac-san,


    1) Please tell us a specification of the response speed on the same color?

    2) We are considering LCOS display.
        The following specifications are required for the LED driver for LCOS display.

            - Channel/Current : 3 channel(G/B/R) / per Min 600mA
            - Switching frequency : excluding AM band (500k to 1.6M Hz)
            - Input voltage range(Min) : Less than 2.9V (Li-ion battery voltage input)
            - The LED can be controlled with the attached waveform.
                *Control can also be considered with an external switch as shown.*

                     

        Are there optimum devices other than the LM3435?
        Is optimum devices a camera flash LED driver like a LM364x?


    Best regards,
    Kato

  • 0 in reply to Junya Kato
    Expert 1635 points

    Attach the figure of the external switch again.

  • 0 in reply to Junya Kato
    TI__Expert 3920 points
    Hi Kato-san,

    We did not test the delay for same color on/off during the evaluation as it was not the purpose to use this device.
    I also cannot comment if you can do the external switch for dimming as the converter was not designed for such condition.

    I am not sure if LM364x family would be able to help as the products were not belong to my product line.

    Sorry if you feel this might not helpful as the product LM3435 was designed a few years back without a broad application usage!