LM3478: Difference between LM3478 and LM3488

Prithvi Raj Narendra1

Part Number: LM3478
Other Parts Discussed in Thread: LM3488, LM5155, LM5156

Hello,

Can I please get the difference between LM3478 and LM3488?

Also I am planning to use such controller as low side buck as shown in below pic. Are there any newer ones apart from these two chips that can do close to 100% duty cycle with internal options for slope compensation.

Thanks, Prithvi

11 months ago

0 Stefan Schauer 11 months ago

TI__Mastermind 42321 points

Hi Prithvi,

thank you for using the E2E forum.

Please see that thread for difference between LM3478 and LM3488

(+) LM3488: LM3488 What is the difference with LM3478? - Power management forum - Power management - TI E2E support forums

Low side N-Mosfet buck converter - Electrical Engineering Stack Exchange

I have not used a low side buck so far, so cannot comment if that will have any issues.

You can also check the LM5155 and LM5156 as alternative parts.

Best regards,

Stefan

0 Prithvi Raj Narendra1 11 months ago in reply to Stefan Schauer

Intellectual 510 points

Thanks Stefan. Can anyone else from TI comment on appropriate chip for low side buck?

0 Stefan Schauer 11 months ago in reply to Prithvi Raj Narendra1

TI__Mastermind 42321 points

Hi Prithvi,

i had some internal discussion and do not see an issue.

Please consider that you still have to maintain the min on time for the duty cycle.

As mentioned also check the LM5155 and LM5156 - they are newer devices and providing more features.

Best regards,

Stefan

0 Prithvi Raj Narendra1 11 months ago in reply to Stefan Schauer

Intellectual 510 points

Thanks for following up. In our use case the min on time is not an issue since the duty cycle is quite high. I see that LM3488 says 100% duty cycle is possible while LM5155/LM5156 say ~93% is possible. In this use case for buck, can they do higher duty cycle that that, say 98-99%?

0 Stefan Schauer 11 months ago in reply to Prithvi Raj Narendra1

TI__Mastermind 42321 points

Hi Prithvi,

the issue with a boost or low side buck is that you can not go too close to 100% duty cycle as at a certain point you will not be able to deliver the energy to the output anymore. This is also based on the right halve plane zero.

Best regards,

Stefan

+1 Stefan Schauer 11 months ago in reply to Stefan Schauer

TI__Mastermind 42321 points

Hi Prithvi,

another issue you might need to solve if you use this architecture is the feedback loop as needed to regulate on Vin - Vout.

So you need to use a current mirror or if the lower accuracy is OK you can use the circuit show here

www.ti.com/.../ucc28880.pdf

Figure 22. Low-Side Buck, Direct Feedback (Level Shifted)

Best regards,

Stefan