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TPS71550 Ldo 5volt reg. burns more times

Other Parts Discussed in Thread: TPS7A4201, LP2950

Good morning,

I just made ​​a circuit with 71550. Input voltage of 18V. Feeds a comparator that activates or deactivates a POWER MOSFET according to the battery  voltage (18V). The MOSFET driving a ON/OFF DC motor.
It happens very often that during power circuit controller 71550 burns. I've already replaced four pieces.
Does anyone know why you can burn quickly so every?
Giovanni Pasolini

  • Hi Giovanni,

    The power dissipation by the LDO (heat) at full load is 650mW for the input voltage in your application. Please see the dissipation rating table on page 2 of the datsheet. At room temperature, the IC can operate up to 320mW so as to not exceed the maximum junction temperature of the device and damage it. You will need to lower the input voltage, lessen the load current, or distribute the heat through series resistors.

    I recommend using the TPS7A4201. This is IC can go up to 28V rated for 50mA and it is in a MSOP package with a powerPAD more capable of dissipating the heat.



  • Hi , Darwin (important family Name)

    thank you, but I think it is a thermal problem.

    If I turn LDO while the MOSFET is off and not by current from the battery to the motor chip never breaks. Turn on or turn off MOSFET without any problems.
    Instead if I turn on LDO while the MOSFET is ON and allows the battery to supply current to the motor, then LDO it burns very often ....
    Perhaps it would serve the electrical design ... more connectio are delete becuse are not connect to any component nor microprocessor

  • Hi Giovanni,

    Yes that is expected. The power dissipation of the LDO is (VIN-VOUT)*IOUT in Watts. When the device does not supply current, power is 0 watts. Since power is not dissipated by the LDO, there is not a rise in temperature. When current is supplied to the load, the temperature increases. For Vin = 18V, Vout=5V, and Iout=50mA, the power is 650mW. For this package, depending on your layout, it can be translated into temperature rise of 205 degC. This exceeds the maximum junction temperature of 150 degC and will damage the IC. Please see page 7 of the datasheet.

  • Hi Darwin,

    like schematic above LDO supply only coparators and fer high value resistors. I thake measure of I input of LDO, its

    is 55uA (micro ampere) so much far from to to thermal limit ... (18-5)*0.055mA= 0.7mW (milliwatt)

    I believe that the problem is not thermic. It's blow at switch ON with MOSFET ON. MOSFET drain current from battery not from LDO.

    LDO supply only Comparator micro power and gate of MOSFET.


  • Hi Giovanni,

    I notice you have 1nF at the output of the LDO. This will effect the stability of the LDO. The minimum effective output capacitance is 470nF or higher ceramic X7R or X5R.



  • Hello Darwin,

    I've just replace LDO with LP2950(51)-5V fixed and seems not suffers same problem. Add some TVS on MOSFET (SMA22V) switch and also to input LDO  (MMBZ27)