TDA7427A Datasheet, PDF (10/21 Pages) STMicroelectronics – AM-FM RADIO FREQUENCY SYNTHESIZER AND IF COUNTER

TDA7427A
The negative input is switchable to three input
pins ( LPIN 1, LPIN 2 and LPIN 3) to increase the
flexibility in application. This feature allows two
separate active filters for different applications
A logical ”1” in the LPIN 1/2 register activates
pin LPIN 1, otherwise pin LPIN 2 is active. While
the high current mode is activated LPIN 3 is
switched on.
INLOCK DETECTOR
The charge pump can be switched in low current
mode either via software or automatically by the
inlock detector by setting bit LDENA to ”1”.
The charge pump is forced in low current mode
when a phase difference of 10-40 µsec is
reached.
A phase difference larger then the programmed
values will switch the charge pump immediately in
the high current mode.
Programmable delays are available for inlock de-
tection.
IF COUNTER SYSTEM (AM/FM/AM - UPC MODES)
The if counter works in modes controlled by IFCM
register (see table):
IFCM1
0
0
1
1
IFCM0
0
1
0
1
FUNCTION
NOT USED
FM MODE
AM MODE
10.7MHz AM UP
CONVERSION MODE
Typical input impedance for IF inputs is 4KΩ.
A sample timer to generate the gate signal for the
main counter is build with a 14-bit programmable
counter to have the possibility to use any crystal
oscillator frequency. In FM mode 6.25KHz in AM
Figure 5. I²C Bus timing diagram
mode a 1KHz signal is generated. This is followed
by an asynchronous divider to generate different
sampling times (see fig. 4).
Intermediate Frequency Main Counter
This counter is a 11/21 bits synchronous autore-
load down-counter. Four bits are programmable
to have the possibility for an adjust to the fre-
quency of the CF filter. The counter length is
automatically adjusted to the chosen sampling
time and the counter mode (AM, FM, AM-UPC).
At the start the counter will be loaded with a de-
fined value which is an equivalent to the divider
value (t_sample ⋅ f_IF).
If a correct frequency is applied to the IF counter
frequency inputs IF-AM IF-FM, at the end of the
sampling time the main counter is changing its
state from 0 H to 1FFFFFH.
This is detected by a control logic. The frequency
range inside which a successful count results is
detected is adjustable by bits EW 0,1,2.
Adjustment of the Measurement Sequence
Time
The precision of the measurements is adjustable
by controlling the discrimination window .
This is adjustable by programming the control
registers EW0...EW2.
The measurement time per cycle is adjustable by
setting the Register IFS0 - IFS2.
Adjust of the Frequency Value
The center frequency of the discrimination win-
dow is adjustable by the control register ”CF0” to
”CF4”. (see data byte specification).
Port Extension and additional functions
Five digital open collector outputs and one digital
push-pull output are available in application
mode. This digital ports are controlled by the data
bits DOUT1-DOUT6.
tHIGH
tR
tLOW
tR
SCL
tSU-STA
SDA IN
tHD-DAT
tHD-STA
tSD-DAT
tAA
tDH
tSUBTOP
ttxt
10/21
SDA OUT
D95AU378