Difference between UCC3854A and UCC3818A

Brian Wang0928

Other Parts Discussed in Thread: UCC3818A, UCC3817, UC3854, UC3854A

Can you offer a difference table between UCC3854A and UCC3818A! it's much easy to compare it and know the main benefits on new one of UCC3818A. Very thanks.

over 11 years ago

0 Mike O' over 11 years ago

TI__Guru 72325 points

I found this old Unitrode presentation showing the differences between the UC3854 and UCC3817. The UCC3818A is very similar to the UCC3817 and the UC3854 is similar to the UC3854A. I hope this helps.

Regards,

0 Brian Wang0928 over 11 years ago in reply to Mike O'

TI__Genius 12370 points

Hi MIke,

It looks you didn't attach the doc.

Could you kindly share the difference list between UC3854 and UCC3817. Very thanks.

0 Mike O' over 11 years ago in reply to Brian Wang0928

TI__Guru 72325 points

Sorry about that, I have attached it for your reference.

Regards,

Transistioning from 3854 to 3817 1 15 2000.ppt

0 Brian Wang0928 over 11 years ago in reply to Mike O'

TI__Genius 12370 points

Hi Mike, There are some questions about the differences between UC3854 and UCC3817.

1. UCC3817 uses the inverter Error-Amp and UC3854 uses the non-inverter Error-Amp. From different circuit configuration of Amplifier, the measured signal of Multiplier is sensed to the invert pin of error amplifier for UCC3817. But UC3854 uses the non-invert pin for multiplier sensing. Why difference configuration can get the same output result of error amplifier? is there any difference function from circuit's point of view? Is it for the leading edge/trailing PWM control?

2. Why does the inverting methold have good noise immulity? Could you explain this more!

Very thanks.

0 Mike O' over 11 years ago in reply to Brian Wang0928

TI__Guru 72325 points

Hello Brian,

1. The UCC3817 uses leading edge modulation so the amplifier had to be inverted.

2. Slide 5 explains why the current amplifier inverting is less noise sensitive. Rf/RI +1 is the gain of a non-inverting amplifier feedback.

The gain on inverting is Rf/Ri which will attenuate noise to less than 1.

Regards,

Mike

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Difference between UCC3854A and UCC3818A