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LM5022: LM5022 & LM5025 Application Question

Kuo Duke
Expert 2040 points
Part Number: LM5022
Other Parts Discussed in Thread: LM5025

Hi Team,

I have LM5022 and LM5025 question need you help, thanks.

a. LM5022
OUT / RT pin of LM5022 have protection when short to GND?

b. LM5022
which pin can implement Latch function? since looks LM5025 can implement by RT pin.

c. LM5022
If use flyback topology, the SS pin can not adjust the rise time by changing Css-pin capacitance. The rise time is fixed.
Can yout provide the reference rise time value or calculate formura?

d. LM5022/LM5025
If the Cvcc-pin over the datasheet recommended, what kinds of problem will happened ?
Because of our customer request, the turn-on  delay needs 400ms.

f. LM5025
The IC OUT_B pin connect a capacitor between IC OUT_B and MosFET

  • 0
    TI__Guru* 75895 points
    Hi Kuo,
    You should split this into two separate post: 1 for the LM5022 and the other for the LM5025. The reason is, these two parts now belong to two different product lines, and they need to be supported separately. We are the group supporting the LM5022.

    Answers to your questions below

    a: It should be current limited but we do not recommend to short RT pin, nor to leave it open.
    b: You can use the UVLO pin. Pulling it to GND will shutdown the IC.
    c: in flyback, SS can still control the rise time, because it can only allow the duty cycle to grow from 0 gradually. A more direct way to control the output rise time is to use an op-amp as the error amp on the secondary side, and soft start the reference voltage of the op-amp by means of RC.
    d: delay should not be implemented with a very large VCC cap. A large cap can over burden the IC's internal VCC regulator. Use delay on EN or UVLO pin is a better choice.
    f: The capacitor invert the OUTB signal such that it can drive a PFET (in the drawing Q2 is a PFET)

    Thanks