8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the TPS61322 device with the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

• Run electrical simulations to see important waveforms and circuit performance

• Run thermal simulations to understand board thermal performance

• Export customized schematic and layout into popular CAD formats

• Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

8.2.1.2.2 Maximum Output Current

For boost converters, the maximum output current capability is determined by the input to output ratio, the

efficiency, the inductor current ripple and the current limit. The maximum output current can be estimated by

Equation 1

OUT

LH

LIM

IN

OUT

V

I

I

V

I

K

u

u

)

2

(

(max)

(1)

where

• ILIM is the peak inductor current limit

• ILH is the inductor current ripple

• η is the boost converter power convert efficiency

Minimum input voltage, maximum boost output voltage and minimum current limit should be used as the worst

case condition for the estimation.

In this example, assume the power efficiency is 70% at the minimum input voltage of 0.9 V. The calculated

maximum output current is 114 mA, which satisfies the application requirements.

8.2.1.2.3 Inductor Selection

Because the inductor affects steady state operation, transient behavior, and loop stability, the inductor is the

most important component in power regulator design. There are three important inductor specifications, inductor

value, saturation current, and dc resistance (DCR).

The TPS61322xx is optimized to work with inductor values between 0.7 µH and 13 µH. The inductor values

affect the switching frequency. The estimated switching frequency in continuous conduction mode(CCM) can

be calculated by Equation 2. The switching frequency ƒSW is not a constant value, which is determined by the

inductance, the inductor current ripple, the input voltage and the output voltage. The current ripple ILH is fixed to

200 mA typically, but it can be affected by the inductor value indirectly. Normally when a smaller inductor value

is applied, the inductor current ramps up and down more quickly. The current ripple becomes bigger because the

internal current comparator has delay to respond. If a smaller inductor peak current is required in applications,

a higher inductor value can be used. However, The inductor and output capacitor must be considered together

for the loop stability. The output capacitor and the inductance will influence the bandwidth and phase margin of

the converter. Consequently, with a larger inductor, a bigger capacitor normally must be used to ensure the same

L/C ratio for a stable loop. For best stability consideration, a 4.7-µH inductor is recommended for 2.2-V output

voltage application.

TPS61322

SLVSDY5E – JANUARY 2018 – REVISED FEBRUARY 2024

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