STA321TR View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

STA321TR

4-channel digital audio system with FFX™ driver

STMicroelectronics 

Electrical specifications

STA321

The STA321 has an integrated oscillator between pins XTI and XTO.

The architecture is a single-stage oscillator with an inverter working as an amplifier. The

oscillator stage is biased by an internal resistor (of about 500 kΩ), and requires an external

PI network consisting of a crystal and two capacitors as shown in Figure 4 below. An enable

feature is provided in bit 7 of register MISC (address 0xC8) to stop the oscillator and thereby

to reduce power consumption.

Not all crystals operate satisfactorily with the type of oscillator used in the STA321. To find

out if a crystal is suitable for this device the following transconductance formula must be

evaluated and compared to the critical transconductance for the embedded oscillator:

Gm = Rm * ω2 * (C + 2 * Co)2 < GmCRITICAL / 3

where ω is the crystal operating frequency, C = CA = CB, Co and Rm are shown in Figure 5

and GmCRITICAL is given in Table 7.

Figure 5. Equivalent circuit of crystal and external components

Table 7. Oscillator specifications

Symbol

Parameter

Min Typ Max Unit

IOSC

Oscillator power consumption with crystal

connected (1)

-

-

215

DutyOSC

TUP

GmCRITICAL

Duty cycle

Startup time

Oscillator transconductance

46.9

-

1060

47.8% 48.9

15 * τx -

-

-

1. If no crystal is connected then the power consumption could be much higher.

2. τx is the time constant of the crystal and external components; a typical value is 44 µs.

µA

%

s (2)

µA/V

18/157

Doc ID 15351 Rev 3

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