saturation current of the inductor must be higher than the calculated peak inductor current. Table 9-2 lists the

recommended inductors for the TPS61033.

Table 9-2. Recommended Inductors for the TPS61033

PART NUMBER

(1)

L (µH)

DCR MAX

(mΩ)

SATURATION CURRENT

(A)

SIZE (LxWxH)

VENDOR

XGL4020-471MEC

0.47

5.1

6.1

4 x 4 x 2.1

Coilcraft

XGL4020-102MEC

1

9.0

3.8

4 x 4 x 2.1

Coilcraft

(1)

See Third-party Products disclaimer

9.2.2.3 Output Capacitor Selection

The output capacitor is mainly selected to meet the requirements for output ripple and loop stability. The ripple

voltage is related to capacitor capacitance and its equivalent series resistance (ESR). Assuming a ceramic

capacitor with zero ESR, the minimum capacitance needed for a given ripple voltage can be calculated by

Equation 9.

OUT

MAX

OUT

SW

RIPPLE

I

D

C

f

V

u

u

(9)

where

• DMAX is the maximum switching duty cycle

• VRIPPLE is the peak-to-peak output ripple voltage

• 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 10.

RIPPLE(ESR)

L(P)

ESR

V

I

R

u

(10)

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 in the range of 4-μF to 1000-μF effective

capacitance. 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.

9.2.2.4 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 10-μF 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 VIN pin. This ringing can couple to the output and be mistaken as loop

instability or could 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.

TPS61033

SLVSGI6 – OCTOBER 2022

www.ti.com

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