TPS2047, TPS2057

TRIPLE CURRENT-LIMITED POWER-DISTRIBUTION SWITCHES

SLVS194 – APRIL 1999

19

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

bus-powered hubs

Bus-powered hubs obtain all power from upstream ports and often contain an embedded function. The hubs

are required to power up with less than one unit load. The BPH usually has one embedded function, and power

is always available to the controller of the hub. If the embedded function and hub require more than 100 mA

on power up, the power to the embedded function may need to be kept off until enumeration is completed. This

can be accomplished by removing power or by shutting off the clock to the embedded function. Power switching

the embedded function is not necessary if the aggregate power draw for the function and controller is less than

one unit load. The total current drawn by the bus-powered device is the sum of the current to the controller, the

embedded function, and the downstream ports, and it is limited to 500 mA from an upstream port.

low-power bus-powered functions and high-power bus-powered functions

Both low-power and high-power bus-powered functions obtain all power from upstream ports; low-power

functions always draw less than 100 mA, and high-power functions must draw less than 100 mA at power up

and can draw up to 500 mA after enumeration. If the load of the function is more than the parallel combination

of 44

Ω and 10 µF at power up, the device must implement inrush current limiting (see Figure 31).

IN1

OC1

EN1

OC3

EN3

2

16

13

12

9

15

6

0.1

µF

10

µF

0.1

µF

10

µF

Internal

Function

OUT1

OUT2

Power Supply

3.3 V

IN2

OC2

NC

14

11

0.1

µF

10

µF

OUT3

NC

10

EN2

NC

3

4

7

8

GND1

GND2

1

5

Internal

Function

Internal

Function

0.1

µF

10

µF

USB

Control

GND

VBUS

D–

D+

TPS2047

Figure 31. High-Power Bus-Powered Function