LP87702 datasheet(80/99 Pages) TI

80 / 99 page

9.2.2.1 Application Components

9.2.2.1.1 Inductor Selection

Section 9.2 shows the inductors L0, L1, and L2. The inductor's inductance and DCR affects the buck and boost

converter's control loop. Table 9-2 lists the recommended inductors, or similar ones, that should be used. Pay

attention to the inductor's saturation current and temperature rise current. Check that the saturation current

is higher than the peak current limit and the temperature rise current is higher than the maximum expected

rms output current. Section 7 shows the minimum effective inductance that ensures good performance. The

inductor's DC resistance should be less than 0.05 Ω for good efficiency at high-current condition. The inductor

AC loss (resistance) also affects conversion efficiency. Higher Q factor at switching frequency usually gives

better efficiency at light load to middle load. Shielded inductors are preferred as they radiate less noise.

Table 9-2. Recommended Inductors for Buck Converters

MANUFACTURER

PART NUMBER

VALUE

DIMENSIONS

L × W x× H (mm)

RATED DC CURRENT,

ISAT max / ITEMP max (A)

DCR typ / max

(mΩ)

MURATA

DFE252012PD-R47M

0.47 µH (20%)

2.5 × 2 × 1.2

5.2 / 4.0(1)

- / 27

TDK

TFM252012ALMAR47MTAA

0.47 µH (20%)

2.5 × 2 × 1.2

5.8 / 4.9(1)

19 / 24

(1)

Operating temperature range is up to 125°C including self temperature rise.

Table 9-3. Recommended Inductor for Boost Converters

MANUFACTURER

PART NUMBER

VALUE

DIMENSIONS

L × W x× H (mm)

RATED DC CURRENT,

ISAT max / ITEMP max (A)

DCR typ / max

(mΩ)

MURATA

DFE252012PD-1R0M

1 µH (20%)

2.5 × 2 × 1.2

3.8 / 3.2 (1)

- / 42

TDK

TFM25201ALMA1R0MTAA

1 µH (20%)

2.5 × 2 × 1.2

4.2 / 3.7 (1)

35 / 42

9.2.2.1.2 Buck Input Capacitor Selection

Section 9.2 shows the input capacitors CIN0 and CIN1. A ceramic input bypass capacitor of 10 μF is required

for both converters. Place the input capacitor as close as possible to the device's VIN_Bx pin and PGND_Bx

pin. A larger value or higher voltage rating improves the input voltage filtering. Use X7R type of capacitors, not

Y5V or F. The capacitor's DC bias characteristics must also be considered. Minimum effective input capacitance

to ensure good performance is 1.9 μF per buck input at the maximum input voltage including tolerances and

ambient temperature range. In addition, Table 9-4 shows how there must be at least 22 μF of additional

capacitance common for all the power input pins on the system power rail.

The input filter capacitor supplies current to the high-side FET switch in the first half of each cycle and reduces

the voltage ripple imposed on the input power source. A ceramic capacitor's low ESR provides the best noise

filtering of the input voltage spikes due to this rapidly changing current. Select an input filter capacitor with

sufficient ripple current rating. In addition, ferrite can be used in front of the input capacitor to reduce the EMI.

Table 9-4. Recommended Buck Input Capacitors (X7R Dielectric)

MANUFACTURER

PART NUMBER

VALUE

CASE SIZE

DIMENSIONS LxWxH

(mm)

VOLTAGE RATING

Murata

GCM21BR71A106KE22

10 µF (10%)

0805

2 × 1.25 × 1.25

10 V

TDK

CGA4J3X7S1A106K125AB

10 µF (10%)

0805

2 × 1.25 × 1.25

10 V

LP87702-Q1

SNVSAL1C – DECEMBER 2017 – REVISED JUNE 2021

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