LM22670 Synchronization. Difference between datasheet versions.

Stephan H.

Other Parts Discussed in Thread: LM22670

Hello,

we are running a prototype with a powersupply using multiple LM22670 in self-synchronized mode. This is achieved by connecting the RT/SYNC pins together and then to GND with a 1k resistor. This is the way how it is described in the datasheet from January 24, 2011. We had no problems so far using it this way.

In the most recent datasheet from March 2013, the circuit is expanded quite significantly by a MOSFET. However, there's no comment why the circuit for this application has changed that much.

So my question is, is it ok to use the old application circuit or is it strongly recommended to include the MOSFET? What are the disadvantages of the old application circuit?

Thanks and regards,

Stephan.

over 10 years ago

0 Frank De Stasi over 10 years ago

TI__Guru 59345 points

The circuit with the MOSFET is the prefered method. Without the use of the FET, the sync function may or may not work correctly.

0 Stephan H. over 10 years ago in reply to Frank De Stasi

Prodigy 90 points

Hello Frank,

thanks for the fast reply.

Could you please be a little more precise, what could happen without the MOSFET? May it happen that only the synchronization doesn't work or may it even happen that the whole supply doesn't work?

Since we have three LM22670, one even for the regulation of a negative voltage, the addition of MOSFETs would require a major redesign of the whole supply.

Thanks and regards,

Stephan.

0 Frank De Stasi over 10 years ago in reply to Stephan H.

TI__Guru 59345 points

Without the FET the device may not synchronize correctly; however the supply should still function.

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LM22670 Synchronization. Difference between datasheet versions.