CS5516-ASZ Ver la hoja de datos (PDF) - Cirrus Logic
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CS5516-ASZ Datasheet PDF : 41 Pages
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CS5516, CS5520
pling is shown on the system connection dia-
grams.
If absolute measurements are to be made by the
CS5516/20, then a precision reference should be
input into the VREF+ and VREF- terminals.
Clock Generator
The CS5516/20 includes a gate which can be
connected as a crystal oscillator to provide the
master clock to run the chip. Alternatively, an
external (CMOS compatible) clock can be input
into the XIN pin. Figure 10 illustrates a simple
model for the on-chip gate oscillator. The on-
chip oscillator is designed to typically operate
with crystal frequencies between 4.0 and 5.0
MHz without additional loading capacitors. If
other crystal frequencies, or if ceramic resona-
tors are used, additional loading capacitance may
be necessary.
XIN
400
22
>1M
To Internal circuitry
400 XOUT
23
1pF
5pF
gm≅ 2000 umhos
5pF
1pF
External XTAL
Figure 10. On-Chip Gate Oscillator Model
The XOUT pin can be used to drive one CMOS
gate for system clock requirements. Be sure to
include the gate’s input capacitance and stray ca-
pacitance as part of the loading capacitance for
the resonating element.
Digital Filter
The CS5516/20 is optimized to operate with clock
frequencies of 4.096 MHz or 4.9152 MHz. These
result in the filter having a 3dB bandwidth of 12
Hz or 15 Hz, with output word rates of 50 or
60 Sps. The rejection at 50Hz ± 3Hz is 70 dB mini-
mum with a 4.096 MHz clock. Similar rejection is
obtained at 60 Hz with a 4.9152 MHz clock.
2244
The digital filter has a deep notch in its transfer
function at 50 Hz (XIN = 4.096 MHz) or 60 Hz
(XIN = 4.9152 MHz) but other XIN frequencies
can be used. The filter transfer function will
scale proportionally. Figure 11 shows the trans-
fer function of the filter when operated at three
different frequencies. With a 3.579 MHz XIN,
the filter offers greater than 90 dB rejection of
both 50 and 60 Hz.
0
-20
(1) XIN = 3.579 MHz
-40
(2) XIN = 4.096 MHz
(3) XIN = 4.915 MHz
-60
-80
-100
-120
-140
-160
0
0
0
21.8 43.7
25 50
30 60
87.3
131.0
100
150
120
180
Input Frequency (Hz)
174.7
200
240
Figure 11. Filter Magnitude Response
218.5
250
300
180
150
120
90
60
30
0
-30
-60
-90
-120
-150
-180
0
XIN = 4.096 MHz
5 10 15 20 25 30 35 40 45 50
Input Frequency (Hz)
Figure 12. Filter Phase Response.
The output word rate of the converter scales
with the XIN clock rate and is set by the ratio of
XIN/81,920; or 50 Sps for XIN = 4.096 MHz. If
very narrow signal bandwidths, such as 3 Hz,
are desired, averaging of the output words is rec-
ommended.
DS74F21
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