BeagleBone Black not powering when battery is absent

Hi everyone,

I am going through initial powerup on a cape I designed, and I have one thing misbehaving: the battery backup circuit. I have the simple circuit depicted below, where the battery is a li=ion cell in a battery clip on the cape.

What I have found is that the board will not power up if the battery is absent. I get brief flashes on the power LED as if it were overloaded.

Experimenting with the BeagleBone with no cape installed, I found that if I installed a 10k resistor between GND (TP8) and TS (TP7) , and a jumper between BAT1/2 (TP5) and BAT_SENSE (TP6), I got the same behavior.

This behavior is present when powered from either USB or VDD_5V via P9. If I install the battery, the board powers up. If I remove the jumper, the board powers up. In fact, if I install a 10k pulldown between BAT1/2/SENSE and GND, the board powers up.

In the TPS65217C datasheet, it implies that an absent battery should not be a problem - but does “absent battery” also mean that BAT_SENSE must be disconnected from BAT1/2? Or could this be an issue with the rise time of my 5VDC coming in? I don’t think this is the case since it does the same thing when plugged in to USB power.

Any insight would be much appreciated!

-Nate