LM34936: LM34936 Low Voltage Input, EVM Modification

Part Number:LM34936

Hello,

I plan on running my application's LM34936 supply off a lithium polymer battery, down to about 3V.  The datasheet says that operation should be possible down to 2.5V with an external BIAS supply.  I ordered an LM34936EVM and modified it to use a separate lab power supply input (remove R17, apply lab input at TP5).  Regardless of whether or not the BIAS voltage was above VCC, the 12V output couldn't hold regulation below approximately 5.5V VIN.  Is this a limitation of the FETs on the board (V_GS), or is there something I'm not understanding about the input/bias topology and operating with an input below 4.2V?

Thanks,

Matt