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I'm trying to use a STOD1317BTPUR DC-DC Boost converter to drive a 12v OLED Display from a 1-cell lipo (~ 3v - 4.5v). The thing is that in the application circuit provided in the datasheet the values for the resistors R1 and R2 are not detailed, neither a formula to obtain them. I've looked for different application circuits from other parts but what confuses me about this one is Vout and Vo_set. I don't understand the difference between them. (I know it has something to do with the LDO it has on the output, but I don't know if this changes something in the formula of the voltage divider).

Application circuit

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    \$\begingroup\$ Can you find the Vfb spec in the datasheet? \$\endgroup\$ – ThreePhaseEel Jan 8 '17 at 5:05
  • \$\begingroup\$ Find FB voltage. Recalculate a resistor devider to match your desired output voltage and said FB voltage. \$\endgroup\$ – winny Jan 8 '17 at 9:55
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Leave it to ST to publish a crap datasheet...

Look at the block diagram. enter image description here

It shows that putting resistors as shown in the application circuit forms a noninverting amplifier with OTA*. There is also a feedback spec. enter image description here

You can use that feedback voltage and your desired output voltage to calculate the voltage divider values.

*OTA usually stands for operation transconductance amplifier. If that is what it actually is, then this answer is wrong. If I was designing with this part, I would reverse engineer an eval board circuit to confirm this hypothesis.

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  • \$\begingroup\$ The thing is that there isn't an eval board for this part (or I haven't found it). So I guess I'll have to make a board and try different values. Thanks anyway. \$\endgroup\$ – Giuliano Scaglioni Jan 8 '17 at 6:01
  • \$\begingroup\$ Odds are it works exactly as I said it does. That's a pretty typical configuration. Shoddy documentation is textbook ST. \$\endgroup\$ – Matt Young Jan 8 '17 at 6:35
  • \$\begingroup\$ In the detailed information (6) it says: In order to guarantee very low ripple on the output voltage, the step-up output is filtered by the LDO. There are two control loops; the LDO control loop regulates VOUT in order to provide the right voltage to the output, while the boost control loop is internally set to provide and output voltage 380 mV higher than VOUT in order to maintain the LDO in regulation at the minimum possible drop. And from here, link, I found that that could be an OTA, and that Vo=Vref*Av. Guess Vref=1.2v?? \$\endgroup\$ – Giuliano Scaglioni Jan 8 '17 at 6:48

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