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Problems with TPS79330

varun perumal
Prodigy 110 points

Hi all,

We are preparing to build a batch 1000 boards based on an msp430 mico-controller. We have chosen to use the TPS79330 LDO to supply 3V to the controller. But in the batch of boards we have, there are quite some issues regarding the regulators:

  1. Firstly some regulators give the same output voltage as the input voltage... does anyone know how this might happen? I  have check and there are no shorts between the pins
  2. Then there is the issue of wildly unstable output, i have used the recommended circut given int he datasheet , but 2/5 LDO's are having an erratic output, the current draw of the board is some 100mA way below the rated 200mA for the regulator

I have been trying to fix this for quite sometime but i dont have a clue as to what is wrong.

Please help, 

Thanks in advance,

Varun

  • 0
    TI__Mastermind 41760 points

    Hi Varun,

    1. For all LDOs the output follows the input when VIN<VOUT(nom)+Vdo or if the IC is damaged. Does the output voltage follow the input all the way up 3.2V or higher? If this is the case, it may be that the ICs are damaged because it should regualte at 3.0V when the input is 3.2V for any load below 200mA.

    2. The LDO can become unstable for certain output capacitors with high ESR. Please see Figure 20 and Figure 21 for stability curves for the output capacitor. Ceramic capacitors should do fine. I recommend 2.2uF (including derating) input and output ceramic X5R capacitors. Be sure these capacitors are close to the IC as possible.  

    If 2/5 LDOs are behaving differently, you make want to check the board (resolder the components, check the ground connection of the IC, or clean the boards) as well.

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Prodigy 110 points

    Hi Darwin,

    1. Yes the voltage is being mirrored for all voltages up to 5V and the load is around 120mA.
    2. I have used 1uF  ceramic and not 2.2uF , ill get a new board made with the values you asked me to put in, and see how it goes.
    3. I have checked the connections with a multimeter, it seems its all fine.
    Should i be looking for pin compatible regulators for a replacement to the ones i have?
    Thanks a lot,
    Varun