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UCC3895: Internal block diagram analysis with DELAB/CD

Shuai Yuan
Intellectual 2290 points
Part Number: UCC3895
Other Parts Discussed in Thread: UCC28C45, UC2845

Tool/software:

Hi Team,

Could you please help share how the CS, ADS pin work to control DELAB/DELCD?

In below diagram, what's Q1 and Q3 initial status, on or off?

When U1 output high, then Q2 will turn on, how about Q1 status and Q2 status? And how the voltage of DELAB changes following the DELAB/CD?

By the way, we have the UCXXX and UCCXXCX family devices, what's the main differences between them, like UC2845 and UCC28C45?

Best regards

Shuai

  • 0
    TI__Guru 73505 points

    Hello,

    What diagram are you refereeing too?  It is not included in your post?

    Regards,

  • 0 in reply to Mike O'
    TI__Intellectual 2290 points

    Hi Mike,

    The below diagram is for your reference. I'm not sure why it didn't show up with last post.

    Best regards

    Shuai

  • 0 in reply to Shuai Yuan
    TI__Guru 73505 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru 73505 points

    Hello,

    Thanks for sharing the block diagram.  I have added some text to your diagram below, to help explain how the circuit works.

    Could you please help share how the CS, ADS pin work to control DELAB/DELCD?

    > Q1 and Q3 are current mirrors, the currents are the same in these FETs

    > Q4 and Q6 are current mirrors, the currents are the same in these FETs.

    > Please note the current is FET Q2 is the same as the current in FET Q1 and Q3.

    > Please note the current is FET Q5 is the same as the current in FET Q4 and Q6.

    > Voltage amplifier A is used to control the voltage across RAB and RCD.  This voltage will control the current in FETs Q1..Q6.

    > The current through resistors RAB and RCD will be used to charge internal timing capacitor (Cdelay) to determine when H bridge FETs A..B will turn on.

    > There is a low pass filter inside (LPF) to filter out noise from the CS and ADS pins.

    In below diagram, what's Q1 and Q3 initial status, on or off?

    >These FETs are used in a current mirror and will have current going through them based on VRDELAB/RAB.

    When U1 output high, then Q2 will turn on, how about Q1 status and Q2 status?

    >FET Q2 and amplifier B form a voltage follower and also in combination resistor RAB control the current through FETs Q1, Q2 and Q3.

    >Please note the currents in Q1, Q2 and Q3 are the same.

    And how the voltage of DELAB changes following the DELAB/CD?

    >The voltage across RCD/RCD = IQ5ds, IQ4ds, IQ6ds.

    >IQ6ds is used to charge internal timing capacitor that is used to determine FET turn on similar to IQ3.

    By the way, we have the UCXXX and UCCXXCX family devices, what's the main differences between them, like UC2845 and UCC28C45?

    >In regards to the UC2845 and UCC28C45.  You will need to repost in the e2e with these part numbers in the title so the appropriate applications engineer >can answer your questions.

    Regards,