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TLC551: Replace TLC551

Part Number: TLC551


I have two PCBs, First one is good, but second one is defective.

I tested the defective board then I found the timer "TLC551CP" is defective, so I took this timer from good PCB and installed it in second PCB then it comes OK.

But I need two PCBs, so I bought a new timer and installed it on the PCB but it is not working, so I compared the resistance between pins of new timer with old timer (which I took from good PCB) and I found it is not same.

The code on old timer (which I took from good PCB) is "601 A N / TLC551CP:
The code on new timer is "64CDAM / TLC551CP

As the following picture:

Please help me to find solution for this problem.


  • Anas,

    I would expect one more character on the top line of the new device. Based on the top marking, I believe the old unit is over 20 years old, maybe even more than 30.

    Where did you purchase the new unit? Did you faithfully follow ESD protection? Generally ESD (electrostatic discharge) is the cause for new parts not working.

    Resistance checking is not always accurate because different DMM use different operating points to check resistance and range changing greatly changes measurement operating point

    Can you provide more details about the resistance results because shorts can easily be check with DMM resistance.
    What is the failure symptom in the application board?
  • Thanks,

    I purchased the new timer from the net and I received it in a silver pocket (I think it is designed for ESD protection).

    The board for motor drive to control the power transistors, the failure is the board not working.

    The resistances are detailed in the following picture:


    - & + (Probe) New Old - & + (Probe) New Old
    1 & 2 > 2 M > 2 M 2 & 1 644 Ω 603 Ω
    1 & 3 > 2 M 1.3 k 3 & 1 514 Ω 457 Ω
    1 & 4 > 2 M > 2 M 4 & 1 588 Ω 595 Ω
    1 & 5 9 kΩ 164 kΩ 5 & 1 9 kΩ 595 Ω
    1 & 6 > 2 M > 2 M 6 & 1 > 2 M 615 Ω
    1 & 7 > 2 M > 2 M 7 & 1 519 Ω 407 Ω
    1 & 8 13 kΩ 240 k 8 & 1 495 460
    5 & 8 4 kΩ 80 kΩ 8 & 5 638 Ω 1.8 kΩ
  • Anas,

    I recommended changing the device with another new device of the same type. 

    I measured current vs. voltage for a TLC551 sample. Very few pins show a linear resistance. This is why DMM resistance checks are not accurate.

    Here is the raw data

    TLC551 pin I,V data.xlsx

  • Thanks,

    I didn't find it in my country.

    I bought from the net but I received it damaged.

    Can you give me a trusted source to buy it?

  • Anas,

    Have you tried the TI store that is available from the product order now page?