UCC29002: Circuit review

KIM Andy

Part Number: UCC29002

My customer is doing load share with UCC29002.

I want to load share two outputs.

The two current deviations are now higher than I thought.

Could you please review the circuit below?

LOAD : 48V, 16.7A

over 7 years ago

0 Benjamin Lough over 7 years ago

TI__Mastermind 27095 points

Hi Kim,

Thanks for your interest in UCC29002. Could you share the full schematic? If you do not want to share it publicly, you can email it to me: ben.lough@ti.com. How much current deviation are you seeing?

Best Regards,
Ben Lough

0 Colin Gillmor over 7 years ago in reply to Benjamin Lough

TI__Mastermind 25570 points

Hi Kim

I'll let Ben work with you but I wanted to point out that the UCC29002 current amplifier is not unity gain stable - it must have a minimum gain of 3 - .

Regards
Colin

0 KIM Andy over 7 years ago in reply to Colin Gillmor

Expert 2530 points

"The current sense amplifier is not unity gain stable and must have a minimum gain of three."

I do not know how to measure the contents of the datasheet.

Can you use an oscilloscope to tell me how to measure it?

Or can you show me a measurement example?

Regards

0 Colin Gillmor over 7 years ago in reply to KIM Andy

TI__Mastermind 25570 points

Hi Andy

The CS amplifier gain is chosen by the user and is set by the ratio of the external resistors from CSO to CS- and from CS- to Rshunt. In the schematic below the gain is R16/R15 = 16200/247 or 65. It is a differential amplifier so the ratio of R14/R13 must be the same as that of R16/R15. I copied the diagram below from the datasheet.

Regards
Colin

0 Colin Gillmor over 7 years ago in reply to Colin Gillmor

TI__Mastermind 25570 points

Hi Andy - Apologies but I forgot to include the diagram

0 KIM Andy over 7 years ago in reply to Colin Gillmor

Expert 2530 points

Good morning

Thank you for your quick reply.

Although it was changed according to the specifications, the current deviation during load sharing was larger.

The first thing I want to ask is whether or not it can be guaranteed in ti when using at high load voltage. The output voltage used now is 48V.

Regards
Andy Kim

0 KIM Andy over 7 years ago in reply to Colin Gillmor

Expert 2530 points

Currently my client pulls power from a 12v line other than at vout to maintain a <15v at vdd voltage.
Could this be related to the current load share circuit not functioning properly?

I checked the ls voltage of two circuits and it was as follows.
Two ADJ voltages were also checked.
Iout = 6.42A for Load 1 and Iout = 5.7 for Load 2.

Regards
Andy Kim

0 Colin Gillmor over 7 years ago in reply to KIM Andy

TI__Mastermind 25570 points

Hi Andy

There is an oscillation on the output current at about 33kHz - the customer will need to identify the source of this instability and fix it. I'd first suggest that they remove the load sharing and verify that the modules are stable. They should also review their compensation networks using the information in the MathCad files in the UCC29002 product folder http://www.ti.com/product/UCC29002/toolssoftware There is a .pdf version of the file at /cfs-file/__key/communityserver-discussions-components-files/196/3113.4571.Mathcad-_2D00_-loadshare_5F00_worksheet_5F00_web.pdf

At any given time the LS pins of the two controllers should be at the same voltage.

I haven't done the calculations because it requires a knowledge of the loop response of the modules in the sharing group but the compensation capacitors at the EAO ouput (2 x 0.26uF) are much smaller than is usual.

In principal the load share controller controls the load current and the output voltage isn't a factor. I'd suggest that the user double check their compensation networks and first solve the oscillation issue and then move on to understanding the reasons for the current imbalance.

Ben may have further suggestions.

Regards

Colin

0 KIM Andy over 7 years ago in reply to Colin Gillmor

Expert 2530 points

Thank you for your quick reply.

I want to know if it is usable under 48v load conditions.

High voltage usage is listed on the datasheet. Using this,

Can you imagine that it works without any problem even at over 48V?

Can you guarantee this at ti?

Regards

Andy Kim

0 Colin Gillmor over 7 years ago in reply to KIM Andy

TI__Mastermind 25570 points

Hi Andy
I answered this question in your re-post at e2e.ti.com/.../2365982

Regards
Colin

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UCC29002: Circuit review