LM5148-Q1: I have a issue about this ic.

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Part Number: LM5148-Q1
Other Parts Discussed in Thread: LM5148

Tool/software:

We are currently encountering some issues with the use of LM5148. The input voltage is set to 22V, and the output is configured for 12V; however, the actual measured output is 0V. Even under no-load conditions, the inductor heats up severely. The board circuit is built on an aluminum substrate. Provided below are the SW waveform of the inductor and the schematic diagram.

1 month ago

0 Timothy Hegarty 1 month ago

TI__Guru 73682 points

The issue here is the FETs are not logic-level gate drive (with Rdson rated at Vgs = 4.5V). The Miller plateau at 5V is too high (should be more like 3V):

Further comments:

Try adding some 10uF/50V/1210 ceramics close to the FETs, as the 100uF/63V electrolytics have high ESR and ESL (these are only good for input filter damping).

Remove the 2.2Ω on the low-side FET gate, as it causes a blip on the gate voltage when the SW voltage slews high.

Regards,

Tim

0 ? ? 29 days ago in reply to Timothy Hegarty

Prodigy 50 points

thanks very much,now there have 12V output,the high FET and inductor heat up severely,all capacitance are ceramics,and the input capacitance are close to high FETs,now i will try the solution you provided.

0 ? ? 29 days ago in reply to Timothy Hegarty

Prodigy 50 points

Can you recommend a suitable MOSFET for me? The package I'm using is SON-8 surface-mount type.

0 Timothy Hegarty 29 days ago in reply to ? ?

TI__Guru 73682 points

An "L" suffix in the MOSFET part number typically designates logic-level gate drive. See the onsemi 80V family of FETs used in this EVM https://www.ti.com/tool/LM5137F-Q1-EVM12V as an example.

0 ? ? 29 days ago in reply to Timothy Hegarty

Prodigy 50 points

thanks for your reply,now i make the PFM pin is high，the circuit can operate normally,why? when PFM is low that the circuit can't work ok.

0 Timothy Hegarty 28 days ago in reply to ? ?

TI__Guru 73682 points

Your MOSFETs are only barely turning on. PFM at light load is worst case. You need to use logic-level FETs with this controller.

Regards,

Tim

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LM5148-Q1: I have a issue about this ic.