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LM25575 inverting buck-boost mode

Alexandre Penaud
Prodigy 60 points
Other Parts Discussed in Thread: LM25575

Hello,

I am designing a +/-12VDC supply based on LM25575 converters used in cascade. The topology consists to create a +12V from 24VDC (coming from PLC backplane). From the +12V we create the -12V by using the LM25575 converter in inverter mode.

The topology and peripherical components comes from the results of the WEBENCH designer tool. However, when I want to simulate the circuit, the -12V polarity doesn't work.

So, I would like to know if the problem comes from the topology or is it a limitation of the model ?

  • 0
    TI__Genius 16025 points

    Hi Alexandre,

    We are looking into your request now and will get back to you shortly.

    Thanks,

    Anston

  • 0
    TI__Genius 15810 points

    Hello,

    Would you please share your schematic and BOM simulated? If required, we could involve the engineers working in the Webench department as well.

    Regards,
    Akshay

  • 0 in reply to Akshay Mehta
    Prodigy 60 points

    Hello,

    Please find hereunder the schmematic issued from Webench designer :

    The TI-TINA file is the following :

    0045.1385.Power_supply_testbench.TSC

    and the associated BOM is :

    2112.2425.BOM_PS_management.txt 
    #	Quantity	Label	Value	
1.	1	R8	 1.02k
2.	1	C26	 1.5n
3.	1	R13	 1.65k
4.	1	C12	 100n
5.	1	C20	 100n
6.	1	C23	 100n
7.	1	C4	 100n
8.	1	C8	 100n
9.	1	C9	 100n
10.	1	R10	 102k
11.	1	R5	 102k
12.	1	C15	 10n
13.	1	C2	 10n
14.	1	C10	 10u
15.	1	C11	 10u
16.	1	R4	 11k
17.	1	R9	 13.7k
18.	1	R12	 14.7k
19.	1	R3	 1k
20.	1	C1	 1u
21.	1	C13	 1u
22.	1	C21	 1u
23.	1	C14	 2.2n
24.	1	C17	 2.2n
25.	1	C6	 2.7n
26.	1	C19	 220n
27.	1	L2	 220u
28.	1	C16	 22n
29.	1	C25	 22n
30.	1	C5	 22n
31.	1	V1	 24
32.	1	R2	 3.09k
33.	1	C24	 33n
34.	1	R14	 36.5k
35.	1	C18	 4.7u
36.	1	C7	 4.7u
37.	1	C22	 470p
38.	1	C27	 470p
39.	1	C28	 470p
40.	1	C29	 470p
41.	1	C3	 560p
42.	1	L1	 56u
43.	1	L3	 56u
44.	1	R1	 8.66k
45.	1	R7	 8.87k
46.	1	R11	 9.09k
47.	1	R6	 9.76k
48.	1	U2	 BYS10
49.	1	D1	 DMBR0540T3
50.	1	D1	 DMBR0540T3
51.	1	U1	 LM5575_TRANS
52.	1	U3	 LM5575_TRANS
53.	1	U4	 LM5575_TRANS
54.	1	V12m	
55.	1	V12V	
56.	1	V5V

    Thanks for your reactivity and your support,

    Alexandre Penaud

  • 0 in reply to Alexandre Penaud
    TI__Genius 15810 points

    Hello Alexandre,

    It looks like you are trying to use TINA to simulate the model. I am going to have to involve the modeling engineers to take a look at why the sim is not working. As such I don't see anything blatantly wrong with the design. Laying it out properly would be very important.

    Regards,
    Akshay

  • 0 in reply to Akshay Mehta
    TI__Intellectual 2930 points

    Hi Alexandre,

    I believe the current TINA model for this was made for Buck topology only.

    Because of the way SPICE sims specially recognize a node 0 as a global GND, even in subcircuits, any internal IC references to 0 in a model make it so its GND referenced, so if in an inverting Buck Boost topology where the IC is referenced to another voltage, the simulation would not function properly.
    So its not a problem with the actual design, its a model issue.

    Best regards,
    Tommy