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3.5 THREE STATE PHASE COMPARATOR
The phase comparator generates a phase error
signal according to phase difference between
f
SYN
and f
REF
. 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 R
ISET
connectedto 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 ’V
REF
’. 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 TESTFUNCTION
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 ”f
REF
in-
put” at pin 7.
3.9 C-BUS INTERFACE
This interface allows communication between the
PLL deviceand
μ
p systems.A bus controlsystem
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 registersis controlledby two address bits.
Test Register
Status
test
0
1
0
0
1
0
0
1
1
1
0
0
Test Function
test
test
2
0
0
0
0
1
PIN9 (TEST/OUT)
PIN 7 (OSCIN)
S
out
(appl.mode) O
scin
(appl. mode)
f
ref
Output
P
hi
Output
f
syn
Output
P
hi
input
O
scin
(appl. mode)
f
ref
Input
fref Input
O
scin
(appl. mode)
TABLE1:
TDA7326
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