TPS6521825_V01 datasheet(95/109 Pages) TI1

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L max

OUT max

OUT

TPS6521825

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SLDS260 – NOVEMBER 2019

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Application and Implementation

6.2.1

Design Requirements

Table 6-1 lists the design requirements.

(1)

Default output voltages shown for TPS65218D0. For other

TPS65218xx variants, refer to DCDC1-4 and LDO1 registers in

Section 5.6.4.

Table 6-1. Design Parameters for TPS65218D0(1)

VOLTAGE

SEQUENCE

DCDC1

1.1 V

DCDC2

1.1 V

DCDC3

1.2 V

DCDC4

3.3 V

DCDC5

1.0 V

DCDC6

1.8 V

LDO1

1.8 V

6.2.2

Detailed Design Procedure

6.2.2.1

Output Filter Design

The step down converters (DCDC1, DCDC2, and DCDC3) on TPS6521825 are designed to operate with

effective inductance values in the range of 1 to 2.2 µH and with effective output capacitance in the range

of 10 to 100 µF. The internal compensation is optimized to operate with an output filter of L = 1.5 µH and

COUT = 10 µF.

The buck boost converter (DCDC4) on TPS6521825 is designed to operate with effective inductance

values in the range of 1.2 to 2.2 µH. The internal compensation is optimized to operate with an output filter

of L = 1.5 µH and COUT = 47 µF.

The two battery backup converters (DCDC5 and DCDC6) are designed to operate with effective

inductance values in the range of 4.7 to 22 µH. The internal compensation is optimized with an output filter

of L = 10 µH and COUT = 20 µF.

Larger or smaller inductor/capacitance values can be used to optimize performance of the device for

specific operation conditions.

6.2.2.2

Inductor Selection for Buck Converters

The inductor value affects its peak to peak ripple current, the PWM to PFM transition point, the output

voltage ripple, and the efficiency. The selected inductor must be rated for its DC resistance and saturation

current. The inductor ripple current (

∆L) decreases with higher inductance and increases with higher VIN or

VOUT. Equation 1 calculates the maximum inductor current ripple under static load conditions. The

saturation current of the inductor should be rated higher than the maximum inductor current as calculated

with Equation 2. This is recommended as during heavy load transient the inductor current will rise above

the calculated value.

(1)

where

•

F = Switching frequency

•

L = Inductor value

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