LM5145: Simulation to Convert +12 V to -48 V

Feiza Alfi

Part Number: LM5145
Other Parts Discussed in Thread: LM5116, CSD18563Q5A

Hello,

I want to create DC-DC Converter using LM5145 to convert +12 V to -48 V.
I still working at simulation level and the result is the output voltage drop before
reach -48 V. How to fix this?

Maximum output current needed is 4 A.

this is simplified diagram for implementation:

simplified diagram for implementation

this is simplified diagram for simulation, i just choose different node
for ground:

this is some simulation result:

inductor current:

inductor current

output voltage:

voltage out

output current:

current output

feedback voltage:

feedback voltage

R_LIM current

simulation file available here: here

over 4 years ago

+1 Timothy Hegarty over 4 years ago

TI__Guru 73072 points

Hi Feliza,

We have an Excel quicktart calculator for inverting buck-boost with the LM5145. See attached as a starting point. The compensation is a bit trickier given the IBB RHP zero and voltage-mode double poles, and it relies on the output cap ESR zero to bring up the phase. One option to consider is a current-mode controller (LM5116 for example), especially at this high power level where the RHP zero is at relatively low frequency.

LM5145 IBB Quickstart r1, VIin= 12V, Vout = -48V, Iout = 4A, Fsw = 250kHz.xlsm

Regards,

Tim

0 Feiza Alfi over 4 years ago in reply to Timothy Hegarty

Prodigy 10 points

Hi, Hegarty

Thank you very much for your response, past days I try to simulate new circuit with component value based on provided LM5145 IBB Quickstart (I modify some parameter).

When I try to simulate using CSD18563Q5A, simulation is not converge, therefore I use BSZ520N15NS3 G (from infineon).

Simulation result are still same, output voltage not reach 48 V.

simulation file available here

simulation result (transient) available here

modified workbook: LM5145 IBB Quickstart r2, VIin= 12V, Vout = -48V, Iout = 4A, Fsw = 300kHz.xlsm

currently I don't have space constraint for PCB implementation, so maybe interleave controller can solve this problem (output not reach target vout)? I will open new thread if interleave controller may solve this problem

0 Timothy Hegarty over 4 years ago in reply to Feiza Alfi

TI__Guru 73072 points

Hi Feiza,

I'm unable to open the files as these file storage sites are blocked. Please ensure that current limit is not engaging during startup.

Note that a current-mode controller such as the LM5116 may provide an easier solution in terms of compensation (relative to a voltage-mode implementation). A two-phase design should not be required.

Regards,

Tim

0 Feiza Alfi over 4 years ago in reply to Timothy Hegarty

Prodigy 10 points

Hi, Hegarty

It's turn out our the shunt resistor setting was wrong. I was not paying attention to RDS(on) setting in the worksheet and now the simulation is working. The RLIM we used in the previous simulation turned out to be smaller than it should be. And current limit are indeed engaged.

The IBB worksheet really help us a lot. thank you for your support

I will mark your first reply as answer

0 Timothy Hegarty over 4 years ago in reply to Feiza Alfi

TI__Guru 73072 points

Hi Feiza,

Thanks for the update.

Regards,

Tim

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LM5145: Simulation to Convert +12 V to -48 V