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TPS63031 regulation in power save mode?

decio.filho
Prodigy 20 points
Other Parts Discussed in Thread: TPS63031, TPS63001

Hello,

I had a previous version of my board I used the TPS63031 with power save mode disabled (PS/SYNC pin wired to VIN). The output voltage was perfectly regulated to 3.3 V. In a new version of the same board, I kept the same basic circuit and changed only the power save mode to enabled by wiring PS/SYNC to ground.

Now, with essentially no load (I estimate at most 10 mA) I'm seeing voltages slightly above 4.0 V in the output. Connecting a 20 ohm resistor to the output lowers the voltage to 3.6 V, which is still far away from 3.3 V even with a somewhat significant load. I tried using 1 uH and 10 uH inductors with no effect in output voltage in the no-load case. The input voltage is about 4.2 V if it matters. I measured the output voltage with an oscilloscope and I see very little ripple, a few tens of mV at most. I'm using about 120u of input capacitance and 20u of output capacitance, all routed close to the IC in the PCB (the same as I used in the previous version of my board where regulation was fine).

I did read in the datasheet that in power save mode the voltage may be above nominal, but I was not expecting it to be off by so much. Plus even if it were, I'd expect to see significant ripple. The TPS63001 datasheet, which as I understand is the same component but with a beefier switch, shows output voltage graphs in power save mode which show a 100 mV ripple, a situation quite unlike what I'm seeing.

So, should I search for a mistake somewhere else in my circuit or the PCB, or can the regulation in power save mode indeed be off by that much.

Thanks

Décio

  • 0
    TI__Genius 17240 points

    There is likely something wrong with your circuit. With PS/SYNC grounded, the unloaded output will be higher only by a few percent. As you mention, with no load the ripple should be higher in this case.  

    Since the version of your board worked with power save disabled, you could have damaged the IC or board in assembly/soldering/testing. Check the feedback pin/resistor divider, it sounds like it might not be connected properly. 

    Please compare your schematic and PCB layout to that of the TPS63030EVM-417.

    Verify connections, component values/placement, trace width and grounds.

    If you are still not able to find the issue please be ready to provide scope shots of the output, switch node, feedback pin and input along with schematics and PCB. 

    You can post these, start a private conversation with me through e2e or I can give you my email address. Let me know.