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Can someone check my layout? I am using TPS63070 buck-boost regulator and I would like to get 4.7 V output at TP12 but, I am getting 11.5 V which is wrong and I don't know why.

Base on the Datasheet R1=R2(Vo/Vref-1) =>
R1=34k(4.7/0.8-1) => R1=165k, R2=34k

Could someone let me know why?

FB: 1.9 mV Vin: 4.7 V. Vout: 5.28 V

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  • \$\begingroup\$ The TPS63070 is internally compensated and intended for use with inductors from 1uH to 2.2uH and certain values of output capacitance. See table 3 in the datasheet. There's no way to know without running an open-loop gain/phase curve to know if it will be stable with lower values of inductance. Have you looked at the output on a 'scope? It could be oscillating. What's your load? \$\endgroup\$
    – John D
    Commented Sep 20, 2018 at 21:14
  • \$\begingroup\$ What do you measure at FB and FB2? \$\endgroup\$
    – winny
    Commented Sep 20, 2018 at 21:15
  • \$\begingroup\$ FB is 1.9V when the voltage is 11 \$\endgroup\$
    – amir
    Commented Sep 20, 2018 at 22:31
  • \$\begingroup\$ @John: I have no load on the output(I even try to put resistor but same) but when I look at the output on the scope it is smooth 11.5V. Regarding the inductor, in the manual page 18, it said it recommended, but you can find it with above formual \$\endgroup\$
    – amir
    Commented Sep 20, 2018 at 23:05
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    \$\begingroup\$ Are you measuring the FB voltage right at the IC? Right between pins 6 & 4? (Not out at the junction of the FB resistors to some local ground). What's the saturation current limit of your inductor (or P/N and datasheet link)? \$\endgroup\$
    – John D
    Commented Sep 21, 2018 at 13:52

1 Answer 1

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It appears you have the correct resistors in place for the feedback circuit. The only thing that appears out of place is the 330nH inductor. Looks like they have a 1.5uH in the data sheet. It should still technically regulate to the voltage you need though..

Have you soldered this part by hand? I've had issues in the past where I've soldered a part incorrectly and then it fails to regulate. (either by damage or bad connections) Always good to check on a development board if you can. TI's are dirt cheap and worth every penny.

Also, is there anything connected to that rail that could a source of back powering? It appears you said you have a power source at about 5.8V but if you have any other power sources in the system I would definitely take a look at that too.

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  • \$\begingroup\$ I solder it by hand but I will take look at it Thanks \$\endgroup\$
    – amir
    Commented Sep 20, 2018 at 20:41
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    \$\begingroup\$ try measuring the voltage on the FB pin \$\endgroup\$
    – BeB00
    Commented Sep 20, 2018 at 20:47
  • \$\begingroup\$ @Jared I have two power supply battery and dc voltage but if I even i use one if it still getting same voltage 10.5-11.5 \$\endgroup\$
    – amir
    Commented Sep 20, 2018 at 23:18
  • \$\begingroup\$ Did you make your own footprint? Definitely go back and cross check your footprint to the data sheet. More details on the batteries would be useful. Also without seeing the rest of the schematic it's up to you to determine if there are any back-powering paths. (think pull-ups, FETs, diodes, etc) If you're measuring the battery voltage through the IC, make sure there's no feasible path that the battery voltage could take. \$\endgroup\$
    – jaredwolff
    Commented Sep 21, 2018 at 16:44
  • \$\begingroup\$ Yes, I made my own footprint and follow the datasheet(attached). I even only solder aboard just with regulator and its parts and give a DC 5v(power supply ) at C1 still I am getting 11v at TP12. One thing I Figure out is the PG pin is low which means "output voltage below power good threshold, in thermal shutdown or input /output overvoltage protection active" base on the datasheet PG 11 \$\endgroup\$
    – amir
    Commented Sep 22, 2018 at 2:20

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