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DCR010505U - heat and no output.

Hamze Hachem
Prodigy 140 points
Other Parts Discussed in Thread: DCR010505

Hello,

I'm an intern at Philips Technologies in Aachen, Germany.

I'm currently troubleshooting a PCB built by a colleague of mine. He has used 8 DCR010505U.  According to this thread http://e2e.ti.com/support/power_management/powermodules/f/501/t/163829.aspx , the DC-DC converters can draw up to 750mA at startup. Could someone comment on that? If this is the case, then that means I need to ensure that at least 6A are supplied at startup, which  would mean I will need to replace the supplying 1A switching regulator (TL2575). This could explain, why so far the output has always been 0.

My colleague seems to have done a mistake while connecting the pins. He connected the SYNC pins together and at the end with the 5V supply voltage. How critical is this? According to the datasheet, it is only required to connect the SYNC pins together.

Any help will be appreciated.

Hamze Hachem

  • 0
    TI__Mastermind 38230 points

    Hamle:

    The sync. pins must never be directly connected to any bus  or 5V. The unit will become extremely hot and can possibly overstress the internal components. The sync. pins can be connected to each other if there is more than1 DCR.

    the maximum  input inrush current can be as high as 750mA. The slope of the  input power source dv/dt and its current rating will affect the  inrush current .

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    Hey Tom,

    Thanks for the fast response. I'm testing 1 DCR010505U to check it is damaged. The SYNC pin is floating, input voltage is 5V, input capacitor 2.2uF and output capacitor 1uF. However the output voltage is too low about 200mV. A TL2575  (max. 1A)  is supplying the component.  Any ideas?

  • 0 in reply to Hamze Hachem
    TI__Mastermind 38230 points

    Thanks for the input. I missed the  8 x DCR010505U  are powered from 5 -1 Amp TL2575.

    The input voltage and input power source is not capabilty of supplying the current necessary to operate the  DCR series.

    The  formula for  input current  is  Input current= Output power( Vout * Iout )/ ( efficiency * input voltage).

    Example  Input current = ( 5Vout)* 0.1Amp ( output current)/ ( 55% efficiency * 5Vin (input voltage) = 181mA input current .

    8 ( number of units ) x181mA 1.45A required by the  5V TL2575  1 amp regulator.

    the inrush current can be as high as 750 Ma fro each DCR010505.

    You must increase the  input power supply to at least 6Amps.

    Tom  

     

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    Hey Tom,

    yes I already know that (check my first post). However, TL2575 should at least be able to supply 1 x DCR010505U, this is does not deliver the promised result (check my last post for more information). Could it be that my colleague damaged the component after connecting SYNC to the supplying voltage? Any other ideas on how to test the component further?

    Thanks in advance

  • 0 in reply to Hamze Hachem
    TI__Mastermind 38230 points

    Hamze:

    Yes the  DCR can be damaged if there is 5V applied directly to the sync. pins.Did you measure the input voltage directly on the  single DCR010505U pins 1or 2 and 27or 28?The sync. pin should not be connected to any other unit or 5Vin.

    Thanks

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    The SYNC pin is floating, power has been cutoff from the other units. relative to pin 27 (0Vin), I get the following results:

    pin1 and pin 2 Vs =5V

    pin27 SYNC= 5V (The unit is on)

    The unit is extremely hot! 

    My guess is, there is something connected to the DCR, that is drawing too much current, so that the voltage is dropped since the unit delivers a power of 1W. But I may be wrong...

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    connected the DCR directly to the PSU. Still no output!

  • 0 in reply to Hamze Hachem
    TI__Mastermind 38230 points

    Hamze:

    The no operation of the DCR010505U which originally  had 5V directly connected to the sync. pin is likely to have been overstressed. the DCR01 will have to be replaced.

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    I disconnected the output circuit from the DCR, now the DCR delivers around 6V. I believe I was right, the output circuit is drawing too much current. Which makes me wonder, does the output current have an upper bound? The datasheet presents only a lower bound of 200mA.

  • 0 in reply to Hamze Hachem
    TI__Mastermind 38230 points

    The DCR010505  absolute operational  maximum output current is 200mA. Any current above this limit can shutdown  the converter.

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 140 points

    Hey Tom,

    I'm still struggling to get my DCRs to work. Below is the schematic :

     

    Only 1 out of 8 DCRs is working properly. I disconneted them all from each other and even replaced the DCRs with brand new ones, but to no avail.

    Here are the voltages I'm getting:

    Working DCR:

    Input: 5V, 30mA

    Sync pin: 1.3V

    Error pin: 5V

    Enable pin: 6.7V

    Vrec: 6.7V

    Vout: 5V

     

     

    The other DCRs:

    Input: 5V 20mA

    Sync Pin: 1.3V

    Error pin: 0V (!!!!)

    Enable pin: 7V

    Vrec: 7V

    Vout: 0.07V

     

    Any ideas?

  • 0 in reply to Hamze Hachem
    TI__Mastermind 38230 points

    I reviewed the schematic. The capacitor C70 must be directly connected to Pin12 Vrec. Remove R 87 and short out its terminations(0Ω)

    DCR internal linear regulator does not  function when the Vrec pin does not have a 1uF ceramic  capacitor .

    Tom