PIN DESCRIPTION

1 - Power Supply (7 pins)

1.1 - Regulator Input Power Supply (VBUS)

This pin must be connected to USB VBUS (+5V).

It supplies the integrated analog USB transceiver.

It is also the positive regulator power supply input

(5V) when ST7554 is in bus-powered mode

(PSM = 1) and it is used to internally generate the

3.3V supply for the digital and analog circuitry.

This pin is the analog power supply input (PSM = 0)

or analog 3.3V power supply output (PSM = 1).

This pin is the positive analog power supply for the

external Codec and DAA.

It is recommended to add a 1

µF capacitor between

VREGA and GNDA as close as possible to the

IC pins.

This pin is the digital power supply input (PSM = 0)

or digital 3.3V power supply output (PSM = 1).

This pin is the positive digital power supply for the

external Codec and DAA.

It is recommended to add a 1

µF capacitor between

VREGA and GNDA as close as possible to the

IC pins.

1.4 - Power Supply Mode (PSM)

This pin controls the VREGD and VREGA power

supply mode.

When PSM = 1, the application is bus-powered.

The 3.3V power supply is generated internally from

VBUS. In this case VREGD and VREGA are out-

puts which can be used to supply 3.3V to external

devices (see Figure 1).

When PSM = 0, the application is self-powered.

VBUS must be still connected to the VBUS Pin of

the USB connector in order to supply the integrated

USB transceiver. Anyway in this case VREGD and

VREGA must be fed by a 3.3V externally regulated

digital and analog power supplies (see Figure 2).

1.5 - Ground (DGND, AGND and GNDBUS)

DGND, AGND and GNDBUS are the digital, analog

and USB ground return pins respectively.

They should be connected together outside the

chip to the GND pin of the USB plug.

8 PSM

5 VBUS

3 GNDBUS

4 VREGD

32 DGND

6 VREGA

7 AGND

ST7554

from USB

to other

digital ICs

to other

analog ICs

Figure 1 :

ST7554 in Bus-Powered mode

(PSM = 1)

8 PSM

5 VBUS

3 GNDBUS

4 VREGD

32 DGND

6 VREGA

7 AGND

ST7554

from USB

from 3.3V

externally

regulated

supplies

Figure 2 :

ST7554 in Self Powered mode

(PSM = 0)

2 - USB Interface (D+ , D-)

These pins are the positive and negative USB

differential data lines. They shall be both connected

to the USB plug or USB protection circuit via 27

Ω

series resistors for line impedance matching.

ST7554

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