TPS54560B: Internal zener diode on EN pin in -Q1 and non-Q1 versions

Roderick Hinman

Part Number: TPS54560B
Other Parts Discussed in Thread: TPS54560

I see that there was a previous question about the difference between the Q1 and non-Q1 versions of the part. Your answer was something to the effect of "no difference in functionality, but more testing for -Q1".

However, I notice on the datasheets for the two parts a difference in section 7.3.7, regarding the EN pin. On the -Q1 data sheet, it says that there is an internal 5.8V zener diode to clamp the pin. On the other data sheet it explicitly says that the user should add an external zener diode to clamp EN if the voltage might rise too high. Is this an actual difference between the two versions, or an error in one of the datasheets?

I ask because I am redesigning a board that has used the TPS54560 (older version, no "B"). The datasheets for it and for its -Q1 version both mention the internal zener. I do not necessarily need the extra testing of the -Q1 part, but the extra cost might be worth it to avoid having to add an external zener diode. And regardless, I do not want to make a mistake with the redesign. Other than the zener, it appears that the "B" part is a drop-in replacement.

Please advise.

Thanks,

Rod Hinman

over 4 years ago

0 Samuel Jaffe over 4 years ago

TI__Mastermind 25590 points

Roderick,

I will check on this and let you know. I should have an answer in a day or two.

-Sam

0 Samuel Jaffe over 4 years ago in reply to Samuel Jaffe

TI__Mastermind 25590 points

Rod,

Information came faster than I thought!

So the zener is still in the B version. The issue is that the current rating is a typical value which is not tested or guaranteed. So customers may undersize the resistors which forces too much current through this zener which may cause damage. We recommend adding a zener as stated in the datasheet if the specs will violate the abs max of the EN pin without the zener.

-Sam

0 Roderick Hinman over 4 years ago in reply to Samuel Jaffe

Prodigy 110 points

Sam,

Thanks for the quick response. Does that mean that the current sinking capability of the zener in the B-Q1 part is tested? Otherwise, why put it in the datasheet?

The Thevenin equivalent of our worst case voltage and the resistive divider is 12.5V through 140k, which means that the internal zener diode (+ internal 10k resistor) would sink about 44 uA. That seems well under the 150 uA value in the datasheet, but of course I don't know how wide the "typical" range is. I suppose it is safer to add the external zener...just need to figure out how to squeeze it in.

Thanks,

Rod

0 Samuel Jaffe over 4 years ago in reply to Roderick Hinman

TI__Mastermind 25590 points

Rod,

No, the zener current sinking capability is not tested in any of those parts.

44uA is small but I would also recommend adding the external zener.

-Sam

0 Roderick Hinman over 4 years ago in reply to Samuel Jaffe

Prodigy 110 points

Thanks.

Power management

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TPS54560B: Internal zener diode on EN pin in -Q1 and non-Q1 versions