LM5176: Parallel operation

John Morrow

Part Number: LM5176
Other Parts Discussed in Thread: LM5170

I am interested in developing a 48 V DC power conditioning device. Essentially we have a source whose voltage can vary from 42 to 56 V and we need to deliver a constant 48V DC output. We also need to be capable of delivering approximately 42 Amps.

I was considering the possibility of employing the LM5176 in parallel operation. I note your Application Report SNVA794-October 2017 on the topic of parallel operation employing droop mode and was wondering if you have a further information that you can provide on the topic – for example is it possible to do this with the LM5176EVM and if so what modifications world be necessary?

One further point if I may, is that I am aware that our expected input voltage maximum of voltage of 56V is too close for comfort to the maxim rated input of the LM5176. Is it permissible to employ some form of voltage attenuation or limiting on the VIN (pin 2) and VISNS (pin3) of the LM5176 i.e. they are not connected directly to the power stage input rail?

Thanking you in anticipation of your reply.

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78440 points

Thank you for considering the LM5176. Yes it can be paralleled. Actually we are working on a simpler scheme to parallel the LM5176, and the engineer is wrapping up the results and putting into an app note. It should be published soon.

56V is also my concern, but it is not the end of the world because it is still below the abs max which is the one you must never exceed. Yes we recommend max operating Vin=55V. However, if you have adequate clamp to prevent the transient voltage from exceeding 60V abs max rating, it should work. The IC pins need to be taken care of in this situation includes all those high voltage pins showing in the ABS Max table in the datasheet. Snubber, TVS, effective filter, all help.

VISNS can be connected to the input line through an resistor. However, the control logic uses the input info, so attenuation is not recommended. VIN pin is the input for the VCC regulator, so large resistor is not recommended.

0 John Morrow over 7 years ago in reply to Youhao Xi

Prodigy 60 points

I am interested in the new app note on parallel operation, when it becomes available.

I'm also looking at the LM5170 and would welcome you advice as to the suitability of these two parts for my application.

Thanking you in anticipation.

0 Youhao Xi over 7 years ago in reply to John Morrow

TI__Guru* 78440 points

Because your input varies from 42V to 56V, and your Vout=48V, you will need a buck-boost. The LM5170 is a bidirectional controller, but it can only do buck in one direction and boost in the opposite direction. In other words, the LM5170 can only support the case where the input and output voltages do not overlap.

I have contacted the engineer and hopefully I can share the circuit diagram for paralleling two LM5176 very soon. The App Note is under way but may take some more time to release.