LP8733 datasheet(63/86 Pages) TI2

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SW_B0

VIN_B0

VIN_B1

VANA

VIN

FB_B0

VOUT_B0

LOAD

SDA

SCL

nINT

CLKIN (GPO2)

GNDs

GPO

SW_B1

FB_B1

PGOOD

VOUT_LDO1

VOUT_LDO0

VIN_LDO0

VIN_LDO1

VOUT_LDO0

VOUT_LDO1

COUT_BUCK0

COUT_BUCK1

COUT_LDO1

COUT_LDO0

CIN_LDO1

CIN_LDO0

CIN_BUCK0

CIN_BUCK1

CANA

CPOL_BUCK

Figure 8-2. Single Dual-Phase Buck Output Configuration

8.2.1 Design Requirements

8.2.1.1 Inductor Selection

The inductors L0 and L1 are shown in the Section 8.2. The inductance and DCR of the inductor affects the

control loop of the buck regulator. TI recommends using inductors similar to those listed in Table 8-1. Pay

attention to the saturation current and temperature rise current of the inductor. 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. The minimum effective inductance to ensure good performance is 0.22 μH at maximum peak

output current over the operating temperature range. DC resistance of the inductor must be less than 0.05 Ω

for good efficiency at high-current conditions. The inductor AC loss 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 8-1. Recommended Inductors

MANUFACTURER

PART NUMBER

VALUE

DIMENSIONS L × W × H (mm)

RATED DC CURRENT

ISAT maximum (typical) /

ITEMP maximum (typical) (A)

DCR

typical / maximum

(mΩ)

TOKO

DFE252012PD-

R47M

0.47 µH (20%)

2.5 × 2 × 1.2

5.2 (–) / 4 (–)(1)

— / 27

Tayo Yuden

MDMK2020TR47MM

0.47 µH (20%)

2 × 2 ×1.2

4.2 (4.8) / 2.3 (2.45)

40 / 46

(1)

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

8.2.1.2 Buck Input Capacitor Selection

The input capacitors CIN_BUCK0 and CIN_BUCK1 are shown in the Section 8.2. A ceramic input bypass capacitor of

10 μF is required for each phase of the regulator. Place the input capacitor as close as possible to the VIN_Bx

pin and PGND_Bx pin of the device. A larger value or higher voltage rating improves the input voltage filtering.

Use X7R type of capacitors, not Y5V or F. Also, the DC bias characteristics capacitors must be considered.

The minimum effective input capacitance to ensure good performance is 1.9 μF per buck input at maximum

input voltage including tolerances, ambient temperature range, and aging (assuming at least 22 μF of additional

capacitance is common for all the power input pins on the system power rail). See Table 8-2.

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

voltage ripple imposed on the input power source. The low ESR of the ceramic capacitor 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.

www.ti.com

LP8733-Q1

SNVSB64A – JUNE 2019 – REVISED JUNE 2021

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