9.2.2 Detailed Design Procedure

9.2.2.1 Setting Output Voltage

The output voltage is set by an external resistor divider (R1, R2 in the Figure 9-1 circuit diagram). For the best

accuracy, R2 should be smaller than 500 kΩ to ensure the current flowing through R2 is at least 100 times larger

than the FB pin leakage current. Changing R2 to lower value increases the immunity against noise injection.

Changing R2 to higher values reduces the quiescent current to achieve higher efficiency at light load.

The value of R1 is then calculated as:

OUT

REF

2

1

REF

(V

V

) R

R

V

u

(5)

9.2.2.2 Inductor Selection

The selection of the inductor affects the steady state of the power supply operation, transient behavior, loop

stability, and boost converter efficiency, the inductor is the most important component in switching power

regulator design. The three most important specifications to the performance of the inductor are the inductance

value, DC resistance, and saturation current.

The TPS61376 is designed to work with inductor values between 2.2 µH and 10 µH. A 2.2-µH inductor is

typically available in a smaller or lower-profile package, while a 10-µH inductor produces lower inductor current

ripple. If the boost output current is limited by the peak current protection of the IC, using a bigger inductance

can maximize the output current capability of the converter.

Inductor values can have ±20% or even ±30% tolerance with 0-A bias current. When the inductor current

approaches saturation level, its inductance can decrease 20% to 35% from the value at 0-A bias current,

depending on how the inductor vendor defines saturation current. When selecting an inductor, make sure its

rated current, especially the saturation current, is larger than boost converter peak current under all operating

conditions.

Normally, it is advisable to work with an inductor peak-to-peak current of less than 40% of the average inductor

current for maximum output current. Follow Equation 6 to Equation 8 to calculate the average, peak and ripple

current of the inductor. To calculate the current in the worst case, use the minimum input voltage, maximum

output voltage, and maximum load current of the application. To leave enough design margin, TI recommends

using the minimum switching frequency, the inductor value with –30% tolerance, and a low-power conversion

efficiency for the calculation.

In a boost regulator, calculate the inductor DC current as in Equation 6.

OUT

OUT

DC

IN

V

I

I

V

u

u K

(6)

where

• VOUT is the output voltage of the boost regulator.

• IOUT is the output current of the boost regulator.

• VIN is the input voltage of the boost regulator.

• η is the power conversion efficiency.

Calculate the inductor current peak-to-peak ripple as in Equation 7.

PP

SW

OUT

IN

IN

1

I

1

1

/

¦

V

V

V

u

u

(7)

where

• IPP is the inductor peak-to-peak ripple.

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TPS61376

SLVSGQ1A – JANUARY 2022 – REVISED SEPTEMBER 2022

Copyright © 2022 Texas Instruments Incorporated

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