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PTH08080W Strange Behavior

Pranjal Chaubey
Prodigy 60 points
Other Parts Discussed in Thread: PTH08080W

Hi 

I have designed a small 5V Power Module using a PTH08080W Module. 

PTH08080W is showing strange behavior, whenever I turn on the power supply (~11V), the output instead of quickly going to 5V, slowly climbs its way taking around 30-45seconds. Sometimes, the output simply get stuck between 3-4V. At this point, if touch the PCB with my fingers, the output instantly jumps to 5V. Also, if I turn on the power while touching the PCB, the output quickly goes to 5V. 

The input capacitor is a 100uF/25V electrolytic. On the output, there's a 100uF/10 electrolytic, a 0.1uF and a 10nF capacitor. Does anybody know exactly what is wrong here? I can put up the PCB design if necessary. 

  • 0
    TI__Mastermind 38230 points

    What are the connections to the PTH08080WAx? What  mechancial version are you using ? And how are the  pins connected to your test board? Check the  input capacitor continuity to the ground and input power source? Check continuity to each pin from your host board assembly.

    1. How is the inhibit pin used? It must be open when the module has an output.

    2. What is the input 11V DC power supply ?  Are you monitoring the input power source ? Is there an y AC component on this 11V power source.?3 What is the output current  during this test. ?

    4. What is the  ESR of the output capacitor, 100uF?

    I t appears you have an intermittent connection between your  board assembly and the module.Check all connections

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    The device in focus here is the through hole version, PTH08080WAH. 

    The board in question is a small manufactured PCB and the device and all other components have been soldered onto it. 

    I have checked the continuity of all the components, including the module and the input capacitor. Everything seems perfectly soldered. 

    1. The inhibit pin is connected to a switch which either shorts it to the ground or leaves it floating. I have tested the switch and its working perfectly fine. 

    2. The power supply used is a bench test power supply having variable voltage output (set to 11.1V in this case). During the tests, its output voltage was being constantly monitored, as it has a voltmeter and an ammeter on-board, and it was very stable. Talking about the AC component, I don't have access to a CRO so I cannot actually 'see' it, but I have a multimeter that can measure AC voltage too. At 11.1V DC, the multimeter showed 9.2V of AC. I am not sure if this is too much, this might be the culprit I believe. 

    3. Initially, I didn't connect any load during the tests. The board has a power indicator LED which consumes less than 15mA of current, this was the only load. Later on, I connected a geared DC motor, consuming roughly 50mA, but the behavior of the power module stayed the same. 

    4. Well, thats one thing that I don't know. But I can assure that these are pretty good ones I have. Shouldn't have a very high ESR rating. 

    After looking at the AC component, I'll arrange for a battery and test my modules again and see if the AC component was playing a spoil sport. 

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    I just tried on with a 11.1V Li-Ion battery pack. Nothing has changed, module is showing the exact same behavior. 

  • 0 in reply to Pranjal Chaubey
    TI__Mastermind 38230 points

    I reveiwed the component details and did not find any information pertaining to the total output capacitance value and its respective  ESR.

    What is the input capacitance value.Is this capacitor directly connected between input Vin(+) and ground. Is there any external capacitance on either the inhibit pin or Voltage adjustment pin?

     

    AC floating on the  input bus can overstress the converter  . When in battery operation the AC component is eliminated . I suspect with very light load and large output capacitance the ramp-up time of the PTH08080 is very soft .

     

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    Caught the real culprit....its the on/off Switch!!! Not sure exactly what is wrong with the switch though, its showing correct operation when I checked it with the multimeter but on removing it from the PCB, the module is working perfectly fine. It might be that pins of the switch weren't soldered properly. 

    I removed the old one and put in a new switch and the whole thing is working perfectly. 

    Thanks for the hep! 

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    An off the topic question,

    Can multiple PTH08080W be connected in parallel to increase the overall current capacity? 

    I connected the 5V outputs of two modules in parallel to see if it works, the modules got very hot and the output voltage also dropped below 4V. So obviously, increasing the current capacity is not as straightforward as I thought. You can surely tell if there is a way.....

  • 0 in reply to Tom Guerin
    Prodigy 60 points

    My current requirement is approximately 8Amps.

  • 0 in reply to Pranjal Chaubey
    TI__Mastermind 38230 points

    If the input voltage is is not greater than  14V maximum, The  power module recommended is PTH08T240WXX or PTH08T241WW( All ceramic capacitors. This module has a 10 amp rating.

    The link to this module is :

    http://focus.ti.com/docs/prod/folders/print/pth08t240w.html

    Tom