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WEBENCH® Tools/LM5176-Q1: LM5176 -Q1

hitainder kaswan
Prodigy 120 points
Part Number: LM5176-Q1
Other Parts Discussed in Thread: LM5176

Tool/software: WEBENCH® Design Tools

Dear All,

 

i am using LM5176 as buck boost converter. today we refer SNVU547–May 2017 application. we found a difference that TI  use some additional components .

Problem 1. SNVU547–May 2017 application note page no 10   resistance R9 value 10 ohm placed between Pin no.2 and diode D3 cathode. but in LM5176 datasheet this resistance is missing. 

                     Why diode D3 needed.

Problem 2. SNVU547–May 2017 application note page no 10   resistance R15 value 2K  placed between Pin no.3 and input supply. but in LM5176 datasheet this resistance is missing. 

                   why there is no diode between 2K resistance Vin.

  • 0
    Genius 4910 points

    Hi Hitainder,

    Regarding the first query, we will ask the concerned expertise to answer it.

    For the second query, the diode you mentioned(between Vin and pin3)  is present in the EVM and datasheet application schematic.

    Regards,

    Atul

  • 0 in reply to Atul_Kulkarni
    TI__Guru* 78440 points

    Thank Atul for chiming in.

    Hi Hitainder,

    Thank you for considering the LM5176.  D3 is used to allow the input voltage to drop below VCC. Otherwise, the VCC would be discharged through the internal LDO's body diode.  R9 is used to form a simple RC filter to remove possible switching noise affecting VIN pin.

    Hope this clarifies

    Best Regards,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 120 points

    Dear Youhao Xi,

    1. R9  10 ohm resistance used, why we are not using 1K or 10K, why we select 10ohm.

    2. we replaced R9 with 0 ohm jumper, we found there is no noise in entire input voltage range,  can we removed it by 0 ohm resistance.

    3. What happen if we short R9 with 0 ohm resistance.

    4.  why we are not using any diode between Vin R15 Pin 3 (VINSYS).

    5. why we are using  R15 resistance value 2K. can we use R15  20E , 100E, 0E, 10K

    6. What happen if we short R15 with 0 ohm resistance.

    Thanks

    Hitainder Singh Kaswan

  • 0 in reply to hitainder kaswan
    TI__Guru* 78440 points

    Hi Hitainder,

    Please read the datasheet and also the IC block diagram carefully.  

    1. VIN in the input pin for the VCC regulator.  If you put 1k or 10k there, you will have a lot of voltage drops, and losses.  It may not work that way. 

    2. Like said, R9 and the C3 forms a filter.Removing R9 does not mean the circuit will not work. It is a good practice to have a small RC filter there. 

    3. You may not see anything happens. 

    4.  VISNS is the input voltage sense pin.  It is a high impedance pin so the 2k won't affect the sensing accuracy. However, if you insert a diode, the diode drop will affect the sense voltage accuracy.

    5. 2k was recommended by the design to make sure the circuit functions under all operating conditions.  It basically add protection in your  input line can be 40V or higher.    

    6. You will lose protection of the IC when Vin reaches 40V or higher.  This is mentioned in the datasheet. 

    Thanks,

    Youhao