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TPS65073 -- won't turn on without a battery

Other Parts Discussed in Thread: TPS65073, TPS65070

I'm trying to use the TPS65073 in a battery-powered product that can also be attached to an "AC" power source or USB power.  I'm worried about the condition where the battery is dead/broken, but the user still wants to turn it on via USB power or wall-wart power.

As shown in the figure below, the PB_IN node is pulled up (internally by the TPS65073) as soon as USB power is connected.  There is no battery or "AC" power connected.  The SYS voltage also comes up immediately, but only to 1 V.  I have an external LDO off of SYS to drive the POWER_ON node, which comes up to ~0.8 V.  The DCDC converters do not power on (shown is the 1.35 V rail, driven off on DCDC3).  Pressing the push button at time = 5 s has no effect.  I get the same results if I try to power on the battery-less device with a wall-wart through the "AC" power input.

My configuration is similar to my post, but I have fixed my earlier issues by connecting VINLDO1/2 to SYS and adding a 10 uF cap to BAT.  The only pins that have no connections are VLDO1, VLDO2, and /reset (pins 2, 4, and 39).  When I have a battery attached, everything works: system powers on with a push button or addition of AC or USB power, system powers off when POWER_ON goes low, system can turn back on after it powers off, can communicate to it via I2C, etc.


Any suggestions would be most appreciated.


  • Based on the TPS65070 datasheet, SYS cannot be loaded during start up


    "SYS Output

    The SYS pin is the output of the power path. When TPS6507x is turned off and there is no voltage at AC or USB, the SYS output is disconnected internally from the battery. When TPS6507x is turned on by pulling PB_IN =LOW, the voltage at SYS will ramp with a soft-start. During soft start, the voltage at SYS is ramped with a 30mA current source until the voltage reached 1.8V. During the soft start, the SYS pin must not be loaded by an external load."


    Also, keep in mind that you either have to follow the conditions as listed in the attached doc or assert POWER_ON while PB_IN is low. 







  • I did have a small (14 mA) load on SYS.  When I removed it, the AC-only and USB-only power on works.