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UCC27524 and UCC27524A

Other Parts Discussed in Thread: UCC27524, UCC27524A, UC3844, UC3854A, UC3845

Please let me ask about UCC27524 and UCC27524A.

UCC27524A has larger input voltage range (INA and INB) than UCC27524.

UCC27524A is -2V to 18V.

UCC27524 is 0V to 18V.

Please let me know the reason why UCC27524A is made.

Is  there any reason?

For example,  UCC27524's D and DGN package are weak to negative voltage?

Or it is just customer's requirement. etc...

[Back ground]

Some UCC27524 broke on my customer's test.

So they are caring about the above.

  • Hello Kohei,

    The reason for having two versions is that UCC27524 is less expensive than the UCC27524A and can be used in applications where negative voltages are not present due to either the nature of the load or it may be the designer's choice to use external circuits, such as snubbers, damping resistors, or careful layout to control these negative voltages. Basically it costs the manufacturer more to produce a chip that has higher negative voltage immunity at a pin.

    The negative voltages come from the output voltage of the PWM IC. Parasitic inductances and capacitances can form a resonant circuit on the traces that go from the PWM IC output to the UCC27524 INA and INB pins. When the PWM pulse signal is applied to this resonant circuit, its fast rise time, approximately 10 ns, causes the voltage to ring, or overshoot in a damped sinusoid. The ring occurs on the falling edge of the pulse as well as the rising edge. This falling edge ring results in a voltage undershoot below ground and can produce negative voltages in excess of a -1V. 

    Some designers choose to add damping resistors to the traces leading to the driver or carefully designing the layout so that the inductive and capacitive parasitics are reduced such that  negative voltages are limited to less than -0.3V.. Some designers place low voltage schottky diodes at the output of the PWM signal to clamp the voltage to less than -0.3V.

    If you cannot add damping resistors or re-layout the traces, I would just replace the UCC27524 with the UCC27524A. The parts are pin for pin compatible.

    Hope this helps,

    Chuck Sampson

  • Chuck-san,


    I appreciate for your support.

    I understood the position of UCC27524 and UCC27524A. In addition, please let me ask additional questions.

    Q1, Have you ever heard that UCC27524 was broken by adding negative voltage to input pin?

    Q2, If the answer for Q1 is Yes, was UCC27524A designed because the breaking of UCC27524 by adding negative voltage occurs often?

    Q3, UCC27524A has only SOIC and MSOP packages. Why weren't SON and DIP packages designed? Is the reason the market demand? Or is there other reason?


  • Kohei,

    Answers to your questions:

    Q1: I don't have any experience with the UCC27524 or UCC27524A. However I have used many PWMICs, UC25701, UC3845,UC3844, UC3854A, etc. All of these older PWM ICs had issues with negative spikes at their pins. The reason for this problem is due to the PN junctions at the pins. They are not meant to be reversed biased which is what happens when a negative voltage is applied at that pin.

    Q2: I can't say for sure since I am not TI representative and have no knowledge of their marketing decisions. Even if I were, I probably wouldn't be allowed to comment. My guess is you are right.

    Q3: Basically the same answer as Q2. Dip packages are not often used in new designs. Although I have seen them used in new high volume designs where size and weight are not an issue. Most new electronics today strive to be light and small -cell phones, Ipads, laptops,etc. So they usually use surface mount. Therefore whatever the big consumers use becomes readily available and cheap. 

    Hope this helps.