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failed LM2577T-ADJ component

Raphael Vanstraelen1
Prodigy 70 points
Other Parts Discussed in Thread: LM2577

Question about the failure mode of the LM2577T-ADJ

I have an old design with a LM2577 adjustable power regulator. It is connected to the 12V battery supply of a lift truck and controls the gear box of the transmission. 

We encounter since the start of 2012  more and more failures on the power supply of our TCU. The LM2577 adjustable power supply IC fails after a while. There was a PCN on the LM2577 in 06/2011. The location of the production site changed.

We see two failure modes on the device:

  1. Some devices gets shorted to ground.
  2. Others become an open circuit and the supply is not boosted anymore to 17,6 V

 

The power supply can change during cranking to a minimum voltage of 5V.

The supply current at the input is at:  

8V   170 mA   Two relays are not switched on at that time and the power consumption is lower.

10V   333 mA    The 2 relays are switched on.(unit is fully operational now)

12V   252  mA   idem

14V   203 mA    idem

We have seen 26 failures on 9411 control units.

 I tried to simulate the failure mode in my lab but was not succesfull. 

What could be the root cause of this failure? Could it be related to the product change? 

Used components are:

L = 150 uH

Rc= 2K2

Cc= 330NF

R1= 13K3  (feedback)

R2=1K (feedback)

Cout=470uF

Cin= not present 

Input is connected to a reverse protection diode and TVS diode of 51V is placed across the supply input. 

 

  • 0
    TI__Genius 16025 points

    Hi Raphael,

    Thank you for your detailed post. Evaluating your operating conditions and environment, I can immediately suggest that the lack of a Cin capacitor could very likely be the cause of failures. In fact I'm thankful the other units survived considering the importance of Cin. 

    Please add a 220uF input capacitor (preferentially electolytic, keeping automotive grade in mind). Also place a small capacitance of .1uF in parallel to bypass any high frequency noise. 

    Also it is common practice to double up on input and output capacitors by serially connecting them but orienting them perpendicular to each other, so if either one cracks, the other can take it's place and not cause failures. This is just precautionary and not mandatory.

    I would also like to examine a copy of your layout. If this is sensitive and you would rather send it through email. You can reach me here: [a*n*s*t*o*n[at]ti[dot]com] (remove *, this is to prevent spam.)

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    TI__Genius 16025 points

    Thread has been taken offline for further discussion owing to sensitive nature of customer's design.

    -Anston