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LMR16006: LMR16006YDDC SHDN

James VDC
Prodigy 240 points
Part Number: LMR16006

Hello,

I am using LMR16006YDDCR based upon a WEBENCH design (thanks for that!).  I have a question that will help in finalizing my design.

1. According to the datasheet, if SHDN is not to be utilized, installing a 100K resistor between VIN and SHDN is recommended.  If one wishes to utilize the SHDN pin and do so from VIN, is it recommended that 100K be used as the value between VIN and SHDN and then calculate the value for the resistor between SHDN and GND accordingly?

  • 0
    TI__Genius 11040 points
    Hello,

    Yes, you are correct. I would recommend calculating the resistor from SHDN to GND with the resistor from SHDN to VIN being 100K.

    Please let me know if you have any additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 240 points
    Thank you Katelyn. One other question; are there any recommended practices for routing the trace to the SHDN pin or location of the divider resistors in relation? And same for the divider connection to ground; can that be a via to the main ground plane of the swps circuit? THANKS!
  • 0 in reply to James VDC
    TI__Genius 11040 points
    Hello,

    You can see the layout of the EVM which includes placeholders for this resistor divider: www.ti.com/.../snvu449.pdf

    Yes, he divider connection to ground can be a via to the main ground plane of the swps circuit.

    Please let me know if you have any additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 240 points
    Thank you Katelyn, I have one of those EVM boards in front of me actually. I was wondering if there is a reason to keep the SHDN divider away from the IC or R3/4 Or was it done so on the EVM layout only to allow the end user an easier time to install the R1/R2 values of their choosing? Thanks for all your help!
  • 0 in reply to James VDC
    TI__Genius 11040 points
    Hello,

    The critical loop for a buck converter is the input capacitors. The input capacitor should be placed as close to the device as possible to minimize any ringing across the input. The SHDN resistor layout is not as critical since this is a logic input. Since VIN is the neighboring pin to SHDN, the SHDN resistors are pulled away from the device so that the input capacitor is placed directly next to the IC.

    Please let me know if you have any additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 70 points

    Hi Katelyn

    I have also a questions according the LMR16006 SHDN pin; can I shut down the controller with an pull down resistor? I am not sure since the datasheet gives no detailed information to the internal pull-up circuit. I use a CAN Transceiver with INH output which is floating in sleep mode. If the Transceiver is in sleep mode, the LMR16006 must shut down. I want to use the INH signal to turn ON / turn OFF the LMR16006. My idea is to connect the Transceiver INH signal to the SHDN pin of the LMR16006 in combination with an pull-down resisor.

    Thanks for any help with that.

    Lukas

  • 0 in reply to Lukas Menzi
    TI__Genius 11040 points

    Hi Lukas,

    The Electrical Characteristics table details the turn on and turn off point (see below).  The device will be enabled when the EN pin sees a voltage greater than 1.3V.  There is a 110mV hysteresis for shut down.  This mean the EN voltage will need to drop 110mV below the turn on point.

    Please let me know if you have any additional questions.

    Best Regards,

    Katelyn

  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 70 points

    Hi Katelyn

    Thanks for your reply. I was not sure if the LMR16006 will turn off when SHDN is only pulled down with an 30k resistor, since there is an unknown pull up circuit in the chip.

    I tried it out now in the lab today and it works, also with 100k pull down.

    Best regards

    Lukas

  • 0 in reply to Lukas Menzi
    TI__Genius 11040 points
    Hi Lukas,

    Great, I am happy to hear that this works. Thank you for sharing.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 240 points
    Thank you Katelyn. With your feedback, I resolved my issues.