TPS65070 How to Enable when Power is Connected to AC pin

Charles Gervasi

Other Parts Discussed in Thread: TPS65070

I have a TPS65070 that is failing to come up on a new board.

I have series resistor from all supplies just downstream from the the inductors and capacitors, allowing me to run the supply completely unloaded. I don't know how well it should work completely unloaded, but I am getting zero volts on all supplies. V[SYS] = V[AC] = 5V. USB and BAT pisn, which are terminated only with 10uF ceramic caps, have almost zero voltage. PB_IN is pulled low. EN_DCDCs are all pulled low (disabled). '65070 default DCDC_SQ[2..0] is '011', which means DCDC3 and DCDC2 should come up without regard to their EN_DCDC pins. My external voltage detect chip would assert DCDC1 when DCDC2 comes up.

My question is what is the next debug step to work out why the part is not coming up. I could try to put small resistor loads on the outputs, but my suspicion is something simply not being enabled.

Thanks!

over 14 years ago

0 Charles Gervasi over 14 years ago

Expert 2270 points

As I said, I have the power supply coming up normally if I pulse PB_IN after input power is applied. My POWER_ON is pulled high just as in the eval board.

Power button in eval board schematic

I have found by experiment that if I tie PB_IN high, the supply comes up. I was under the impression that you didn't need an edge on PB_IN to make the supply start up if POWER_ON is asserted.

My only question at this point is how I should connect POWER_ON and PB_IN such that the supply starts up as soon as power is applied.

Thanks!

0 Daniel Acevedo over 14 years ago in reply to Charles Gervasi

TI__Genius 17240 points

Are you powering with USB, AC or BAT?

0 Charles Gervasi over 14 years ago in reply to Daniel Acevedo

Expert 2270 points

We are powering it from 5V applied to the AC pin. USB and BAT are not used and therefore just terminated with caps. The PMIC provides that power for a board that is one of many boards in instrumentation system. We want it always on when 5V is applied.

Do you have a recommendation on what to do with the PB_IN pin?

Thanks!

0 Daniel Acevedo over 14 years ago in reply to Charles Gervasi

TI__Genius 17240 points

In the case where the supply is to power up when 5V is applied to the AC pin, the pin named PB_IN (which has an internal pull-up to AVDD6) should be left open and pin POWER-ON needs to be pulled high. If the TPS65070 is powered from the BAT pin, PB_IN needs to be tied low to start the converters.

0 Charles Gervasi over 14 years ago in reply to Daniel Acevedo

Expert 2270 points

Do you know of any negative consequences of simply tying PB)INline to 5V?

0 Daniel Acevedo over 14 years ago in reply to Charles Gervasi

TI__Genius 17240 points

Charles,

I don't think there would be any negative effects if you connected /PB_IN high, though it is unnecessary. How are you pulling /PB_IN high? Are you connecting it directly to the 5V line? Please post your schematics and a scope shot of the voltage at the /PB_IN pin on the device demonstrating the behavior.

Thanks,

Daniel

0 Charles Gervasi over 14 years ago in reply to Daniel Acevedo

Expert 2270 points

I realized I could remove a resistor on my board and float the pin. Floating the pin works as well as tying it high. Thanks for your help!

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TPS65070 How to Enable when Power is Connected to AC pin