[FAQ] TPS546D24S: I have been using the TPS546D24A, now I see the TPS546D24S. What are the differences?

Peter James Miller said:

Is the TPS546D24S compatible with TPS546D24A designs?

Yes, the TPS546D24S is pin-to-pin and drop-in compatible with TPS546D24A designs.  An existing TPS546D24A design should work exactly as it did with a TPS546D24A when populated with a TPS546D24S as long as the system firmware is tolerant of the updated IC_DEVICE_ID Suffix (last byte) and ID_DEVICE_REV

Peter James Miller said:

I know the TPS546D24 uses different pin-programming resistors than the TPS546D24A, Does the S use resistors from the TPS546D24 for the TPS546D24A?

The TPS546D24S uses the same pin-programming resistor values as the TPS546D24A did, and the same programming resistors will select the same options.

Peter James Miller said:

Did anything else about the TPS546D24A change in the TPS546D24S?

No changes were made to the existing features of the TPS46D24A in the TPS546D24S, but some new PMBus features were added.

Peter James Miller said:

What's new about the TPS546D24S?

The TPS546D24S adds new security features to the PMBus designed to limit write access to PMBus commands.

EXT_WRITE_PROTECT which provides the user with greater flexibility in write protecting groups of functionally related PMBus commands to limit configuration changes that will be accepted by the devices, including the ability to prohibit write-access to EXT_WRITE_PROTECT, permanently locking write access to protect the configuration from changes by a malicious actor who has gained access to the PMBus

PASSKEY which provides a 16-bit passcode.  When a non-zero value is stored to PASSKEY at RESTORE or Power On, the PASSKEY command prevents write access to STORE_USER_ALL and EXT_WRITE_PROTECT, allowing a user to select an intermediate level of protection between permanently locking EXT_WRITE_PROTECT and leaving EXT_WRITE_PROTECT unlocked.  To minimize sensitivity to brute-force attacks, the PASSKEY will disable after 3 failed attempts each AVIN power cycle.

To improve security, TI recommends customers programming PASSKEY:

1) Program MFR_MODEL and MFR_SERIAL with unique identifiers

2) Program PASSKEY with a private-key hash of MFR_MODEL and MFR_ID (and other protected information) in order to use a unique but discoverable PASSKEY for each system.  This will prevent a malicious user who has gained access to 1 device from being able to gain access to all similar devices.

If EXT_WRITE_PROTECT will not be used, users can program it to 8000h to lock access to EXT_WRITE_PROTECT.

Peter James Miller said:

Will the TPS546D24A be discontinued with the release of the TPS546D24S?

There are no plans to discontinue or end of life the TPS546D24A.  TI expects to continue producing both the TPS546D24A and TPS546D24S for the foreseeable future.

Peter James Miller said:

I don't see a TPS546B24S or TPS546A24S version on TI.com, will there be an S version of the TPS546B24A and TPS546A24A?

Yes, the TPS546B24S and TPS546A24S are coming soon!