• L is the inductor value.

• ƒSW is the switching frequency.

• VOUT is the output voltage.

• VIN is the input voltage.

Therefore, the peak current, ILpeak, seen by the inductor is calculated with Equation 8.

PP

Lpeak

DC

I

I

I

2

(8)

With ISEL pin logic high, the peak switching current limit is 4.5 A(typ), when the ISEL pin logic low, the peak

switching current limit will change from 4.5 A(typ) to 2.5 A(typ). It is important that the peak current does not

exceed the inductor saturation current.

For a given physical inductor size, increasing inductance usually results in an inductor with lower saturation

current. The total losses of the coil consists of the DC resistance (DCR) loss and the following frequency-

dependent loss:

• The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)

• Additional losses in the conductor from the skin effect (current displacement at high frequencies)

• Magnetic field losses of the neighboring windings (proximity effect)

For a certain inductor, the larger current ripple (smaller inductor) generates the higher DC and also the

frequency-dependent loss. Usually, a data sheet of an inductor does not provide the core loss information.

If needed, consult the inductor vendor for detailed information. An inductor with lower DCR is basically

recommended for higher efficiency. However, it is usually a tradeoff between the loss and foot print. The table

below lists some recommended inductors.

Table 9-2. Recommended Inductors

PART NUMBER

L (μH)

DCR TYP (mΩ)

SATURATION

CURRENT (A)

SIZE (L × W × H mm)

VENDOR(1)

XGL5050-222ME

2.2

6.8

10.7

5.28 x 5.48 x 5.1

Coilcraft

XGL5050-472ME

4.7

13.9

7.0

5.28 x 5.48 x 5.1

Coilcraft

XGL6060-103ME

10

18.5

7.3

6.51 x 6.71 x 6.1

Coilcraft

XGL4020-222ME

2.2

19.5

6.2

4.0 x 4.0 x 2.1

Coilcraft

XGL4020-472ME

4.7

43

4.1

4.0 x 4.0 x 2.1

Coilcraft

XGL4020-822ME

8.2

71

3.2

4.0 x 4.0 x 2.1

Coilcraft

(1)

See the Third-party Products Disclaimer.

9.2.2.3 Bootstrap Capacitor Selection

The bootstrap capacitor between the BST and SW pin supplies the gate current to charge the ISO FET device

gate during the turn on of each cycle. The gate current also supplies charge for the bootstrap capacitor. The

recommended value of the bootstrap capacitor is 0.47 μF to 1 μF. CBST must be a good quality, low-ESR ceramic

capacitor located at the pins of the device to minimize potentially damaging voltage transients caused by trace

inductance. A value of 0.47 μF was selected for this design example.

9.2.2.4 Input Capacitor Selection

Multilayer ceramic capacitors are an excellent choice for the input decoupling of the step-up converter since

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 22-µF input capacitor or equivalent is sufficient for the most applications, larger

values can be used to reduce input current ripple.

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, such as from a wall adapter, 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 can even

damage the device. Additional "bulk" capacitance (electrolytic or tantalum) in this circumstance, must be placed

TPS61376

SLVSGQ1A – JANUARY 2022 – REVISED SEPTEMBER 2022

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