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LM5150-Q1: LM5150 Iq issue in low input voltage no load condition..

fangxing sun
Intellectual 310 points
Part Number: LM5150-Q1

I use LM5150 make a pre-boost circuit. But I found the issue when input voltage lower than 6.7V and no load condition, Iq will increase to 18mA.  Increase input voltage higher than 7V Iq return normal 1-2mA.

The Below picture is my schematic. Please help me find which reason cause this issue.

LM5150.pdf

  • 0
    TI__Mastermind 46905 points
    Hi Tyrael,

    The expert supporting this device is out of office. The question is assigned to him. He will reply next week.
  • 0
    Intellectual 310 points
    I check DEMO board have same issue. and I found VSET value have some relationship with this question.
    When VSET value= SS 6.8V input voltage need drop to 5V Iq will increase. Vset value= ss 7.5V. input voltage need drop to 5.8V Iq will increase.

    And I check LM5150 specification. SS mode is fix-PWM mode, EC mode is PFM mode. But I check when Low Iq condition LM5150 is not Fix-PWM mode.
  • 0 in reply to fangxing sun
    TI__Mastermind 21720 points
    Hi Tyrael,

    Where are you measuring the current draw? Are you trying to operate in SS (Stop-start) or EC (emergency call) mode?

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Intellectual 310 points

    I use Keithley power supply 2280S-32-6 to measure input current.

    Yes, I try SS and EC mode. EC mode Iq is lower than SS mode.

    I confuse why input voltage has effect Iq at SS mode no load condition.

    I have concern EC mode compare to SS mode whether have different at load and transient performance. Please help me check this portion.

    Thanks

  • 0 in reply to fangxing sun
    TI__Mastermind 46061 points
    Hi

    Please refer the Figure13 in the datasheet.
    If the VOUT regulation target is 6.8V, the boost converter enters in and out the standby mode and its Iq is small if the input voltage is greater than 5V. If the input voltage is less than 5V in this configuration, the converter keeps switching at every cycle and its Iq becomes high.
    If the VOUT regulation target is 7.5V, the boost converter enters in and out the standby mode and its Iq is small if the input voltage is greater than 5.8V. If the input voltage is less than 5.8V in this configuration, the converter keeps switching at every cycle and its Iq becomes high.
    Regards,
    EL
  • 0 in reply to EricLee
    Intellectual 310 points
    Hi Lee

    Thanks for your reply. But this reply is base on our test result explain, I understand.
    I want to know the reason why LM5150 keeping switching lower one input threshold.
    BTW If Vset=10.5V which input voltage LM5150 will into keeping switching condition. How to calculate this value.
    Thanks.
  • 0 in reply to fangxing sun
    TI__Mastermind 46061 points

    Hi

    Please see the section 7.4.3.1  in the datasheet. If the one of the inequalities (#10 and #11) is true, the device enters standby mode and eventually the VOUT will move up and down between Standby threshold and Wakeup threshold. Please see the area "B" in the Figure 13 which is below. If the device works in this "B" area, the input current will drop to save battery drain.

  • 0 in reply to EricLee
    Intellectual 310 points
    Hi Eric

    Thanks for your reply I understand.
    Another question If i want LM5150 higher efficiency in light load and lower input voltage. So I think should change to EC mode.
    But I concern EC mode load transient performance is not good. Could help me check this portion.