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uc2625 intermittent failure to drive phases

Carlos Medica
Prodigy 10 points
Other Parts Discussed in Thread: UC2625

I have an BLDC motor which we developed in the late 90's.  At that time the application note had a .1uF  capacitor connected between pin 24 (SSTART) and ground.  At the time we were using a UC1625 Mil Rated chip.  We recently assembled a batch of 25 of these motors using a UC2625N chip and found that some (2) units would intermittently fail to produce phase drives while receiving Hall sensor inputs.  Upon checking we found that pin 24 in those units was low in those instances.  Upon checking, we found that the newer application notes for the UC2625 controllers have pin 24 pulled up to Vref with a 51K resistor, besides having the .1uF capacitor to ground.  Has anything changed in the internal works of the UC2615 chip, and should we redesign that board to incorporate the pull up resistor?

  • 0
    TI__Mastermind 20985 points

    Hi Carlos,

    It appears to me that the device hasn't changed, but later it was found that a 51k resistor ensures proper operation.  The last sentence for the SStart description was added in an updated datasheet: "A 51-kO resister is added between VREF and SSTART to ensure switching."  I suggest your boards incorporate this.

    Best regards,
    RE