ICL7662 vs TC7662

Discussion in 'General Electronics Chat' started by hoveringuy, May 1, 2010.

  1. hoveringuy

    Thread Starter New Member

    May 1, 2010
    2
    0
    I have had some failure recently using TC7662 charge pumps to create negative voltages for an automotive application.

    ICL7662 had been what I was using before but has been backordered so I used the compatible TC7662 with some resulting failures.

    Questions: What is the difference between ICL and TC in the name designation?

    My failure appear to happen at start-up, so I think I may have a latch-up issue.

    The TC7662 data sheet has a note:

    If the voltage supply driving the TC7662B has a large
    source impedance (25-30 ohms), then a 2.2​
    μF capacitor
    from pin 8 to ground may be required to limit the

    rate of rise of the input voltage to less than 2V/
    μsec.

    What is the reason for this, and would an automotive battery require a capacitor?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Automotive environments are amongst the most brutal on the planet, thermally, shock/vibration and electrically.

    You can get heavy surges when "load dumps" occur (like turning off headlamps); the transients can go past 60v for a few milliseconds. Adding a low-pass filter between the electrical system and your IC will help a great deal to slow down these transients.
     
  3. hoveringuy

    Thread Starter New Member

    May 1, 2010
    2
    0
    What's curious is that I haven't had a single failure while the circuit has been operating; the failures have been occuring at start-up.

    I will add a small current limiting resistor and filter cap to see if it makes a difference. It appears that I am getting a latch-up somehow.

    Is there any reason a low ESR tantalum capacitor would adversely affect a charge pump?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Not that I know of. Poly metal film or ceramic should be adequate. You may have problems with tantalums if you get high transients on the input. Tantalums tend to go off like firecrackers if their limits are exceeded.
     
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