I just realised that the pin counts of the LX7167 and LX7167A are wrong. I still think the chip is made by Microsemi, and I know it is a stepdown switchmode converter, but I'm wondering if it could indeed be an LX7167B, with a different pin count to the LX7167/A versions. The other possibility is NX7167B, but I haven't been able to find either.
I think the other number is probably a YYWW (Year/Week) date code. This could be confirmed by comparing the date codes on the other chips.
Edit: It's an LX7157B.
LX7157B, Microsemi (MSC), step-down PWM regulator IC with integrated high side P-Ch MOSFET and low side N-CH MOSFET, 2.2MHz, 3V to 5.5V:
http://www.microsemi.com/document-portal/doc_download/124259-lx7157bdshttps://upload.wikimedia.org/wikipedia/commons/d/d7/Seagate_ST1000LM014_-_controller-8425.jpg