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TPS22976

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SLVSDE7 – NOVEMBER 2016

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Copyright © 2016, Texas Instruments Incorporated

Typical Application (continued)

10.2.1 Design Requirements

Table 3 shows the TPS22976 design parameters.

Table 3. Design Parameters

DESIGN PARAMETER

VALUE

Input voltage

3.3 V

Bias voltage

5 V

22 µF

Maximum acceptable inrush current

400 mA

10.2.2 Detailed Design Procedure

10.2.2.1 Inrush Current

When the switch is enabled, the output capacitors must be charged up from 0 V to the set value (3.3 V in this

example). This charge arrives in the form of inrush current. Inrush current can be calculated using Equation 1.

Inrush Current = C × dV/dt

where

•

C is the output capacitance

•

dV is the output voltage

•

dt is the rise time

(1)

The TPS22976 offers adjustable rise time for VOUT. This feature allows the user to control the inrush current

during turnon. The appropriate rise time can be calculated using Table 3 and the inrush current equation. See

Equation 2 and Equation 3.

400 mA = 22 μF × 3.3 V/dt

(2)

dt = 181.5 μs

(3)

To ensure an inrush current of less than 400 mA, choose a CT value that yields a rise time of more than 181.5

μs. See the oscilloscope captures in the Application Curves section for an example of how the CT capacitor can

be used to reduce inrush current.