LP5813 datasheet(49/60 Pages) TI

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• VIN is the input voltage of the boost converter

Therefore, the inductor peak current is calculated by Equation 10.

∆ILP =∆ILDC +∆ILP−P2

(10)

Inductor peak-to-peak current is recommended to be designed less than 40% of the average inductor current,

with maximum output current setting. Large inductor value reduces the magnetic hysteresis losses in the

inductor and improves EMI performance with small inductor ripple, but the load transient response time

increases. The saturation current of the inductor must be higher than the calculated peak inductor current.

Table 10-2. Recommended Inductors

Part Number

L (µH)

DCR MAX (mΩ)

SATURATION

CURRENT (A)

SIZE L×W×H (mm)

VENDOR

XEL4030-102ME

9.78

9.0

4.0 × 4.0 × 3.1

Coilcraft

74438357010

13.5

9.6

4.1 × 4.1 × 3.1

Wurth Elecktronik

HBME042A-1R0MS-99

11.5

7.0

4.1 × 4.1 × 2.1

Cyntec

10.2.3.2 Output Capacitor Selection

The output capacitor is selected to meet the requirements of output ripple and loop stability. The ripple voltage is

related to capacitor capacitance and equivalent series resistance (ESR). Assuming a ceramic capacitor with zero

ESR, the minimum capacitance for a given ripple voltage can be calculated by Equation 11.

COUT= IOUT×DMAX

fSW×VRIPPLE

(11)

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 12.

VRIPPLEESR =ILP ×RESR

(12)

The derating of a ceramic capacitor under dc bias voltage, aging, and ac signal need to be considered during

design. For example, the dc bias voltage can significantly reduce capacitance. A ceramic capacitor can lose

more than 50% of capacitance at the rated voltage. Therefore, enough the voltage rating margin must be left to

get adequate capacitance at the required output voltage. Increasing the output capacitor can make 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. 10 μF effective capacitance is recommended in typical application, which means around 22 μF

rated capacitance. If the output capacitor is below the range, the boost regulator can potentially become

unstable.

10.2.3.3 Input Capacitor Selection

Multilayer X5R or X7R ceramic capacitors are excellent choices for the input decoupling of the integrated boost

converter, because of the extremely low ESR and small footprint. Input capacitors must be located as close as

possible to the device. While a 10-μF input capacitor is sufficient for most applications, large capacitance is used

to reduce input current ripple. When the input power is supplied through long wire and only ceramic capacitor

is put, the load step at the output induces ringing at the VIN pin. This ringing couples back to the output and

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LP5813

SNVSC74 – SEPTEMBER 2023

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