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I need a power supply that delivers 12v with an input between 8v and 35v. That's the reason I bought a couple of TPS55165Q1 from Texas instruments. I've made 3 different PCBs with a similar circuit. All of them works great in buck mode, delivering 12v up to 500mA. When I change to boost mode, It does not deliver neither the current or voltage it was calculated. When I switch to low-power mode, it works just as expected in buck and boost mode. That's why I conclude that there is a protection thats working (in Low Power mode, all protections are disabled). I've tried to emulate as close as possible the circuit of Figure 3 of its evaluation board: http://www.ti.com/lit/ug/slvuay1/slvuay1.pdf

I show you

schematicenter image description here

I've chosen SRU1048-4R7 inductor from Digikey and take special care of its Rdc and peak current. All capacitors are ceramic except for the 100uF. Can you give me some advice in order to get it work? Thanks!

** EDIT ** I attach some oscillograms. It was taken with a Vin of 14.8v (Step-up mode) measurement of time measurement of voltage

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    \$\begingroup\$ Please explain "When I change to boost mode", "When I switch to low-power mode". What do you do? Be specific. \$\endgroup\$ – winny May 16 at 10:33
  • \$\begingroup\$ Hi winny. The module has to switch automatically between buck and boost mode depending on its supply voltage. So if I just simply power up the supply with a voltage above 15v (aprox) it will work in buck mode. Below this value, it works in boost mode. To switch to low-power mode, the PS pin does the job. When I power up the circuit with PS connected to main supply, It works in low power mode. \$\endgroup\$ – Gonzalo Cervetti May 16 at 10:40
  • \$\begingroup\$ So you lowered the voltage? At what point did what happen? Show oscillograms. Main supply? You mean Vin? \$\endgroup\$ – winny May 16 at 10:57
  • \$\begingroup\$ I edited my question with oscillograms. Yes I lowered the voltage to 14.8v so the step-up mode starts. Yes, sorry for my bad english: Main supply = Vin \$\endgroup\$ – Gonzalo Cervetti May 16 at 11:59
  • \$\begingroup\$ Why would the converter step up 14.8 V to 12 V? Does not make sense. What does your oscillograms show? What's the problem? \$\endgroup\$ – winny May 16 at 12:06

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