TDA7326 datasheet(9/16 Pages) STMICROELECTRONICS

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3.5 THREE STATE PHASE COMPARATOR

The phase comparator generates a phase error

signal according to phase difference between

fSYN and fREF. This phase error signal drives the

charge pump current generator

3.6 CHARGE PUMP CURRENT GENERATOR

This system generates signed pulses of current.

Duration and polarity of those pulses are deter-

mined by the phase error signal. The absolute

current values are programmable by ’CURR1’

and ’CURR2’ bits and controlled by an external

resistor RISET connected to Pin 2 and GND.

3.7 LOW NOISE CMOS OP-AMP

A low noise Op-Amp is available on chip. The

positive input of this Op-Amp is connected to an

internal voltage divider and to Pin 3 ’VREF’. The

negative input is connected to the charge pump

output. In cooperation with this internal amplifier

and external components, an active filter can be

provided. To increase the flexibility in application

the negative input can be switched to two input

pins (Pins 15 and 16). This switch is controlled by

’LPF’ register with ’LPF’ low Pin 15 is active and

’LPF’ high Pin 16 is active. This feature allows

two separate active filters with different perform-

ance.

3.8 TEST FUNCTION

The test pin (Test Out) is used only for testing: it

has no use in real applications. The three bits

test0, test1, test2, of the test REGISTER must be

programmed as 0,0,0 in application.

Some device internal signals can be checked at

pin 9 (TST OUT) and pin 7 (OSC IN) by program-

ming different codes of the test register according

to the Table 1.

For example by programming the code 110 the

”fsyn out” will be available at pin 9 and ”fREF in-

put” at pin 7.

3.9 C-BUS INTERFACE

This interface allows communication between the

PLL device and

µp systems. A bus control system

check the format of transmission, only eight bit

word transmission is allowed. Four registers with

6 bit are user programmable. The selection of this

four registers is controlled by two address bits.

Test Register

Status

Test Function

test

PIN9 (TEST/OUT)

PIN 7 (OSCIN)

Sout (appl. mode) Oscin (appl. mode)

fref Output

Oscin (appl. mode)

Phi Output

fref Input

fsyn Output

fref Input

Phi input

Oscin (appl. mode)

TABLE 1:

TDA7326

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