SWCS049G datasheet(124/144 Pages) TI

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OUT

OUT max

IND

124

TPS65911

SWCS049S – JUNE 2010 – REVISED AUGUST 2018

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Applications, Implementation, and Layout

Table 7-2. External Component Recommendation (continued)

PARAMETER

TEST CONDITIONS

MIN

NOM

MAX

UNIT

CO filtering capacitor ESR

500

mΩ

LDO7

Output filtering capacitor (CO(LDO7))

0.8

2.2

2.64

µF

CO filtering capacitor ESR

500

mΩ

LDO8

Output filtering capacitor (CO(LDO8))

0.8

2.2

2.64

µF

CO filtering capacitor ESR

500

mΩ

VRTC LDO

Input capacitor (CI(VCC7))

X5R or X7R dielectric

4.7

µF

Output filtering capacitor (CO(VRTC))

0.8

2.2

2.64

µF

CO filtering capacitor ESR

500

mΩ

BACKUP BATTERY

Backup battery capacitor (CBB)

2000

Series resistors

CBB = 5 mF to 15 mF

1500

7.2.2.2

Controller Design Procedure

Follow these steps to design the controller:

1. Design the output filter

2. Select the FETs

3. Select the bootstrap capacitor

4. Select the input capacitors

5. Set the current limits

VDDCtrl requires a 5-V supply at the V5IN pin with an input capacitor. For most applications, a 1-μF, X5R,

20%, 10-V, or similar capacitor must be used for decoupling.

7.2.2.2.1 Inductor Selection

An inductor must be placed between the external FETs and the output capacitors. Together, the inductor

and output capacitors make the double-pole that contributes to stability. In addition, the inductor is directly

responsible for the output ripple, efficiency, and transient performance. As the inductance increases, the

ripple current decreases, which typically results in an increased efficiency. However, with an increase in

inductance, the transient performance decreases. Finally, the selected inductor must be rated for the

appropriate saturation current, core losses, and DC resistance (DCR). Use Equation 1 to calculate the

recommended inductance for the controller (L).

where

•

VOUT is the typical output voltage.

•

VIN is the typical input voltage.

•

fSW is the typical switching frequency.

•

IOUTmax is the maximum load current.

•

KIND is the ratio of ILripple to the IOUTmax. For this application, TI recommends that KIND is set to a value

from 0.2 to 0.4.

(1)

After selecting the value of the inductor, use Equation 2 to calculate the peak current for the inductor in

steady state operation, ILmax. The rated saturation current of the inductor must be greater than the ILmax

current.

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