• IOUT is the maximum output current

• fSW is the switching frequency

The ESR impact on the output ripple must be considered if tantalum or aluminum electrolytic capacitors are

used. The output peak-to-peak ripple voltage caused by the ESR of the output capacitors can be calculated by

Equation 7.

RIPPLE(ESR)

L(P)

ESR

V

I

R

u

(7)

Take care when evaluating the derating of a ceramic capacitor under dc bias voltage, aging, and ac signal. For

example, the dc bias voltage can significantly reduce capacitance. A ceramic capacitor can lose more than 50%

of its capacitance at its rated voltage. Therefore, always leave margin on the voltage rating to ensure adequate

capacitance at the required output voltage. Increasing the output capacitor makes the output ripple voltage

smaller in PWM mode.

TI recommends using the X5R or X7R ceramic output capacitor with 10μF effective capacitance when output

current is lower than 1A, and 20μF effective capacitance when output current is higher than 1A. The output

capacitor affects the small signal control loop stability of the boost regulator. If the output capacitor is below the

range, the boost regulator can potentially become unstable. Increasing the output capacitor makes the output

ripple voltage smaller in PWM mode.

For large output capacitance more than 40μF application, TI recommends a feedforward capacitor to set the

zero frequency (fFFZ) to 1kHz, and also recommend to connect a 50ohm resistor series with the feedforward

capacitor to filter some high frequency noise coupled from VOUT to FB.

7.2.2.3 Input Capacitor Selection

Multilayer X5R or X7R ceramic capacitors are excellent choices for the input decoupling of the step-up converter

as they have extremely low ESR and are available in small footprints. Input capacitors must be located as close

as possible to the device. While a 22μF/0603 input capacitor is sufficient for most applications, larger values may

be used to reduce input current ripple without limitations. Take care when using only ceramic input capacitors.

When a ceramic capacitor is used at the input and the power is being supplied through long wires, a load step

at the output can induce ringing at the input voltage. This ringing can couple to the output and be mistaken as

loop instability or even damage the part. In this circumstance, place additional bulk capacitance (tantalum or

aluminum electrolytic capacitor) between ceramic input capacitor and the power source to reduce ringing that

can occur between the inductance of the power source leads and ceramic input capacitor.

7.2.3 Application Curves

VIN = 3.3V, VOUT = 5V, IOUT = 1A

Figure 7-3. Switching Waveform at Heavy Load

VIN = 3.3V, VOUT = 5V, IOUT = 100mA

Figure 7-4. Switching Waveform at Light Load

TPSM81033

SLVSHL0D – JUNE 2024 – REVISED DECEMBER 2024

www.ti.com

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