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LM5150-Q1: Boost Operation Not happening with External Load

Sumit Singh
Prodigy 110 points
Part Number: LM5150-Q1
Other Parts Discussed in Thread: TPS3760,

Tool/software:

Hello Team,


We are using part->LM5150QRUMRQ1 in our design.
When the load is not connected at Output of Boost Converter. The boost operation is happening, But as soon as we connect the load-0.150A, the boost operation is not happening
After application of load current, AVCC voltage is also decaying and is not fixed at 5V.

Can you please support on debugging this issue?

Attached are schematics of this IC and other waveform captures

Regards

Sumit

LM5150Q_Boost_Schematics.pdf


Boost Output Without Load


Boost Output with Load



AVCC Without Load



AVCC With load


Boost Switching



  • 0
    TI__Mastermind 29900 points

    Hi Sumit,

    Thanks for using the e2e forum.
    Could you add the following information:

    Input voltage range
    Output voltage
    Maximum load conditions

    Based on this I will review the design and look for possible root causes.

    Thanks and best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 110 points

    Hello Niklas,

    Below are asked details->
    Vin- 3V-4.2V
    Vout-6.8V
    Iload-150-200mA

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    There are two things to look at:
    - If the green signal in the oscilloscope screenshot is the Boost_EN signal in the schematic, you can see that the controller is periodically disabled / enabled.
    Can you permanently connect the EN pin to VOUT, to see if that works?
    - I would also ask you to verify if the supply can really deliver the peak current that is necessary to charge the intuctor.
    This peak current is much higher than the average load current and the supply must not limit it.

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 110 points

    Hello Harry,

    Yes the Green Signal is ENABLE signal and the voltage level is HIGH enough to be detected as HIGH and I have zoomed and checked in oscilloscope, there are no transitions in the signal

    Regarding your 2nd point, I have connected input of boost to external power supply set to 3.8V- Supply is capable of giving 30V, 30A max. So there is no issue with sourcing capability of powersupply

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    You wrote:
    >> I have connected input of boost to external power supply set to 3.8V- Supply is capable of giving 30V, 30A max.

    The device will not properly start-up when you just supply 3.8V.

    See page 7 of the datasheet:
    (2) The device requires minimum 5V at VOUT pin to start up

    You will need to supply more than 5V first. When it already boosts, you can reduce the input voltage to 3.8V


    What is that noise in the green signal in the second image?
    In the working condition in image 1 it does not exist.

    For further tests, please disconnect that voltage monitor and permanently connect the EN signal to a high enou8gh voltage (e.g. VOUT).


    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 110 points

    Hello TI Team,

    After connecting EN pin directly to VOUT, BOOST Operation with Load is happening properly.

    But when we connect to EN pin through TPS3760- intended path, we are not seeing the Boost operation happening with Load ON condition? Why is this behavior?
    NOTE- TPS3760 IC is programmed/set to provide Enable Output when Battery Voltage drops to 4.5V. Is that OK?
    I changed the configuration to 5V and checked with Enable path of Boost connected to TPS3760 O/P.. When i am slowing decreasing the VBATT voltage, BOOST is happening with LOAD ON COnditions also, but when we SWITCH OFF the VBATT Suddenly, BOOST is not happening with LOAD ON Condition.

    Please respond asap. 

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    Good to hear that you are making progress and that the LM5150 Boost operation is fundamentally working.

    I am not at all familiar with the TPS3760, so I cannot help you with that.

    In this forum, the questions are routed to the experts that are responsible for the products in the title/subject of a thread.
    Therefore, this thread (LM5150-Q1: Boost Operation Not happening with External Load) has reached me.

    May I ask you to open a second thread with your particular questions about the TPS3760, please?

    Thanks and regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 110 points

    Hello Harry,

    I have validated the working of TPS3760 and now even with EN Pin connected to TPS3760 control, it is working now with LOAD Condition.

    However, I am seeing the below issues with LM5150 Boost still->

    1) When the load current is set to 100mA , BOOST Operation is happening and O/P Voltage is regulated to 6.8V.
    However, when we increase the Load Current to 150mA, we see that BOOST o/P Voltage drops to 5.6V. Why is this happening?
    I have checked it in both ways, with ENABLE pin connected to O/P of Boost and also when it is connected to TPS3760 Output, in both cases same behavior is observed.

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    So far I had only focused on your fundamental problem, so I did not verify each component of your schematic.

    For a proper operation it is mandatory that you properly calculate all components.
    For this purpose, please use the QuickStart Calculator which you can download from our website:
    https://www.ti.com/tool/download/SNVC214 
    Fill in the parameters in the yellow fields.

    You will find that a 33uH inductor is much too big.
    Also, a 500 Milliohm sense resistor is much too big.
    Please change these components according to the calculation results for your application (about 7uH and 130 Milliohm).

    Finally, I have recognized, that you are not using any electrolytic capacitor on the output side.
    This may have an impact on the ripple on the output.


    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 110 points

    Hello Harry,

    Thanks for your detailed response.

    During the design phase I had used this excel document. I am not sure why it had suggested higher inductor value. Attached is the same excel. Can you once check if the excel file had any issue.Skylark_LM5150 quick start 09282017.xlsx

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    Please fill in the correct input voltages and output current that you7 gave:

    Vin= 3V .. 4.2V
    As "typical" input voltage, I would use some voltage close to the lower end.
    Iload max = 200mA

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 110 points

    Hello Harry,

    Thanks for your response. Attached is the updated sheet.
    Can you please check and let me know if these component values are correct?

    2656.Skylark_LM5150 quick start 09282017.xlsx

  • 0 in reply to Sumit Singh
    TI__Mastermind 19595 points

    Hello Sumit,

    The numbers in the spreadsheet are looking good to me now.

    The only issue with the spreadsheet is that in line 90 it expects a bulk capacitor which is bigger than the minimum number in line 89.

    So, if I take 10µF from the ceramic capacitance (line 91) and move that to line 90, so that it shows 10 (bulk) + 22 (ceramic), the calculations in the spreadsheet will work properly.

    In reality, 32µF all ceramic will work as well if there are no big steps in the load.

    Please make sure that the saturation current of the inductor will be 0.9A or more.

    For ell capacitors, please use low ESR and low ESL versions and please consider the DC BIAS as well as aging effects.


    All information in this correspondence and in any related correspondence is provided “AS IS” and “with all faults” and is subject to TI’s Important Notice: www.ti.com/.../important-notice.shtml

    Best regards
    Harry