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DLP4620SQ1EVM: Ask for DLP4620EVM FFC(LED Drive signal)

Kim Yangrae
Prodigy 70 points
Part Number: DLP4620SQ1EVM
Other Parts Discussed in Thread: LM3409, LM61480

Tool/software:

We're trying to design a new laser driving circuit that doesn't use the LM3409.

The signals that control the time domain from the formatter board to the LED driver board are as follows:
- "PMIC_(R/G/B)EN"
- "PMIC_SEN1"
- "PMIC_LM3409_DRVEN"

I understand that the "turn-off signal", corresponding to Dimming and "COMP",
is merged into the "PMIC_LM3409_DRVEN" signal to inactivate the LM3409 and control brightness.
The "PMIC_(R/G/B)EN" and "PMIC_SEN1" signals are used to control the timing of each color of the LED using a power MOSFET.

1. The question here is, aren't driving the enable pin low to disable the driver and shutting it off with a power MOSFET essentially the same thing?
I understand that "PMIC_SEN1" is necessary to quickly drain the node's residual power,
but wouldn't it be more effective to also force "PMIC_LM3409_DRVEN" to be inactive at the "PMIC_SEN1" timing?

2. The board you're testing in the second half of the year processes DUTY_OUT (appears to be for dimming)
generated by PWM and SEQ_CLK, and SEN1, (RED/GRN/BLU) EN signals with logic gates and feed them to the FET gate driver.
Is there a separate reason for not touching the LM61480's Enable pin? Isn't enabling PMIC_LM3409_DRVEN necessary to turn it off at the COMP timing?

3. If I process the signal coming from the FFC cable as follows, will there be any problem with the operation of the TPS99001?

(1) "PMIC_LM3409_IADJ" is a variable resistor that tunes the voltage of the LM61480 and is not used.

(2) "PMIC_LS_SENSE_P" is connected to the common cathode of the laser, "PMIC_LS_SENSE_N" is connected to GND,
and a 10mohm sensing resistor is connected between the common cathode and GND.

(3) "PMIC_REN", "PMIC_GEN", and "PMIC_BEN" are similar to your suggestion.
They process the external PWM signal (Default High) and the "PMIC_SEN1" signal with a logic gate and apply them to the power MOSFET.


(4) PMIC_CMODE and PMIC_SEN1 are used as is in the existing circuit.

(5) PMIC_LM3409_DRVEN is connected to the EN pin of the LM61480.

(6) To set the LM61480 to 2.2MHz, the RT pin is connected to GND, and for CCM, the SYNC/MODE pin is connected to the internal VCC. Since it is connected, PMIC_LM3409_SYNC will not be used.

4. Also, is LED_ANODE_DEVIDED for watchdog purposes? Does it not cause any problems if it's not connected at all? If it does, how do you handle it?

5. When you were testing, the anode-ground shunt due to PMIC_SEN1 and the PMIC_CMODE were blank. Are these things okay to remove?

  • 0
    TI__Intellectual 1750 points

    Hello  ,

    Thank you for reaching out and using the E2E forums! An expert from our team will review the thread and get back to you shortly.

    Regards, 

    Tristan Bottone

  • 0
    TI__Expert 6730 points

    Hi Kim Yangrae,

    Kim Yangrae said:
    1. The question here is, aren't driving the enable pin low to disable the driver and shutting it off with a power MOSFET essentially the same thing?
    I understand that "PMIC_SEN1" is necessary to quickly drain the node's residual power,
    but wouldn't it be more effective to also force "PMIC_LM3409_DRVEN" to be inactive at the "PMIC_SEN1" timing?

    Please read through this technical article about LED dimming in switch-mode LED drivers such as the LM3409. At high switching speeds, the shunt model greatly outperforms the FET option because it keeps a continuous inductor current. When using a FET, the inductor will have to ramp up, slowing the switching speeds (and worsening dimming factor).

    If using the shunt model, the current only needs to know if it needs to go to the LED or if it needs to be shunted around the LED.

    I will let Aaron, who has been helping you offline, answer the other questions. Please continue to keep in contact with him.

    Regards,
    Michael Ly

  • 0 in reply to Michael Ly
    Prodigy 70 points

    Here are some quick things I'd like to check:
    1. What is the purpose of the PMIC_ANODE_DIVIDED signal on the FFC cable?
    Also, if the function is not used, how should it be set: Float, GND, or High (at what voltage)?

    2. For current regulation in the DLP4620EVM system, is the analog dimming (ILIM) feedback from the technical article you mentioned PMIC_LM3409_IADJ and the Digital PWM Dimming Enabling (PMIC_LM3409_DRVEN) feedback from PMIC_LS_SENSE_N and PMIC_LS_SENSE_P correct? What is the specific purpose of the PMIC_LS_SENSE_N and PMIC_LS_SENSE_P feedback?

    3. PMIC_LM3409_IADJ is difficult to use with the TPS61480. If I don't use it, will it cause any system problems if I leave it as Float?

    4. The high-speed switching circuit you're testing in the second half of the year doesn't use PMIC_CMODE. Is it okay to eliminate the charge/discharge element for Shunt, as in the past?

  • +1 in reply to Kim Yangrae
    TI__Expert 6730 points

    Kim,

    1. LED_Anode divided was not used in the previous design, but in the concept we provided, the voltages from the peak detector are monitored by the ADC for current control purposes
    2. This is for current-level sensing. The concept we provided for HSPWM does not use this. The HSPWM signals are too fast to sense, which is why we use the peak.
    3. This will not cause any problems if you leave it floating
    4. For this, you can eliminate this charge/discharge element, as the existing HSPWM design does not make use of this

    Regards,
    Michael Ly