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PDR_ON errata on LQFP100 for STM32F4

Question asked by Jack Peacock on Aug 19, 2013
Latest reply on Sep 3, 2013 by John F.
A warning so no one else will get caught by this.  On the original STM32F4 design docs pin 99 on LQFP100 is shown as RFU or PDR_ON, and diagrams show it can be connected to Vdd.  The gotcha is this only applies to rev Z parts, first release.  Read on if you got some Z parts for prototyping.

A later errata (and I missed this) changes pin 99 to Vss for rev A parts, after rev Z.  If the PCB connects pin 99 to Vdd you get a power supply short.  Just got a batch of PCBs back with rev A parts installed, all have Vdd shorted to ground.

It may also casue a problem if you use an external reset and connect it to pin 99 as a PDR_ON pin (as shown on some diagrams) to enable the power supervisor.  It will pull down the external reset to Vss.  PDR_ON has been removed from LQFP100 packages.

The change doesn't apply to 144 and 176 pin parts.  I believe the 64 pin part doesn't have an RFU pin.
  Jack Peacock