Adjusting Boost Converter Voltage

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Based on knowledge base guidance for designing feedback networks and the TPS61085 datasheet:
  • The TPS61085’s internal reference (V_FB) is 1.229 V (from the datasheet).
  • In our schematic, the lower feedback resistor (R2) is 18.2 kΩ.
  • The output voltage equation is:
    VOUT=VFB(1+R1R2)V_{OUT} = V_{FB}\Bigl(1 + \frac{R1}{R2}\Bigr)
    Rearranged for R1:
    R1=R2(VOUTVFB−1)R1 = R2\Bigl(\frac{V_{OUT}}{V_{FB}} - 1\Bigr)
  • Plugging in V_OUT = 8 V, V_FB = 1.229 V, and R2 = 18.2 kΩ:
    R1=18.2 kΩ×(81.229−1)≈100 kΩR1 = 18.2\,\text{kΩ}\times\bigl(\tfrac{8}{1.229}-1\bigr)\approx 100\,\text{kΩ}
    (Calculator result: 1.0027×10^5 Ω)
Thus, choosing a standard 100 kΩ resistor for R1 ensures the booster regulates to 8 V.
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@library find a 100 kΩ 0603 resistor for R1

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Here are the top 3 matching 100 kΩ, 0603 resistors:

Table

Part NameManufacturerResistanceTolerancePower RatingPackageAvailabilityLinkDatasheet
CRCW0603100KFKEAVishay Dale100 kΩ±1%0.1 W0603Digi-Key, Mouser, Arrow, LCSCView in LibraryPDF
RMCF0603FG100KStackpole Electronics Inc100 kΩ±1%0.1 W0603Digi-Key, MouserView in LibraryPDF
RMCF0603FT100KStackpole Electronics Inc100 kΩ±1%0.1 W0603Digi-Key, Mouser, ArrowView in LibraryPDF
Recommendation: All three are 100 kΩ ±1% thick-film resistors in 0603 with 0.1 W rating. The Vishay CRCW0603100KFKEA has the highest usage count and broadest distributor support, making it a robust choice for R1.
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Files

Schematic

Layout

3D View

C3
Capacitance
1.1nF
C1
Capacitance
10uF
R2
Resistance
18.2kΩ
L1
Inductance
3.3uH
R3
Resistance
51kΩ
D1
R1
Resistance
158kΩ

TPS61085 Reference design tiHX