TUSB8042AI datasheet(48/64 Pages) TI2

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Figure 9-16. High-Speed Downstream Port 1

Figure 9-17. High-Speed Downstream Port 2

Figure 9-18. High-Speed Downstream Port 3

Figure 9-19. High-Speed Downstream Port 4

9.3 Power Supply Recommendations

9.3.1 TUSB8042A Power Supply

Implement VDD and VDD33 as a single power planes.

• The VDD pins of the TUSB8042A supply 1.1V (nominal) power to the core of the TUSB8042A. This power rail

can be isolated from all other power rails by a ferrite bead to reduce noise.

• The DC resistance of the ferrite bead on the core power rail can affect the voltage provided to the device

due to the high current draw on the power rail. The output of the core voltage regulator can be adjusted to

account for this, or a ferrite bead with low DC resistance (less than 0.05Ω) can be selected.

• The VDD33 pins of the TUSB8042A supply 3.3V power rail to the I/O of the TUSB8042A. This power rail can

be isolated from all other power rails by a ferrite bead to reduce noise.

• All power rails require a 10µF capacitor or 1µF capacitors for stability and noise immunity. These bulk

capacitors can be placed anywhere on the power rail. Place the smaller decoupling capacitors as close to the

TUSB8042A power pins as possible with an optimal grouping of two of differing values per pin.

9.3.2 Downstream Port Power

• The downstream port power, VBUS, must be supplied by a source capable of supplying 5V and up to 900mA

per port. Downstream port power switches can be controlled by the TUSB8042A signals. It is also possible to

leave the downstream port power always enabled.

• A large bulk low-ESR capacitor of 22µF or larger is required on the VBUS pin of each downstream port to

limit in-rush current.

• The ferrite beads on the VBUS pins of the downstream USB port connections are recommended for both

ESD and EMI reasons. A 0.1µF capacitor on the USB connector side of the ferrite provides a low impedance

path to ground in case a fast rise time ESD current coupled onto the VBUS trace from the cable.

TUSB8042A

SLLSF93A – JUNE 2019 – REVISED JANUARY 2025

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