CS5520-BSZ Cirrus Logic Inc, CS5520-BSZ Datasheet - Page 22

• Manufacturer Part Number: CS5520-BSZ
• Description: IC ADC 20BIT BRIDGE TRAS 24-SOIC
• Manufacturer: Cirrus Logic Inc

Specifications of CS5520-BSZ

• Number Of Bits: 20
• Sampling Rate (per Second): 60
• Data Interface: Serial
• Number Of Converters: 2
• Power Dissipation (max): 37.5mW
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 598-1102-5

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s ho uld no t be ap plied prior to the
CS5516/CS5520 being powered-up. With EXC,
F1, and F0 set to logic 0, the BX1 output will be
logic 0 (0 volts) and the BX2 output will be a
logic 1 (+5 volts).
A second method for configuring the converter
for dc excitation is by setting EXC = 1, and
pulling up BX1 (pin 12) to VD+ (pin 20)
through a resistor. This sets the converter for
use with external excitation which uses the
BX1 pin as an input to set the excitation fre-
quency. With BX1 = VD+, the external
excitation frequency is zero, or dc.
AC Bridge Excitation
AC bridge excitation involves using a clock sig-
nal to generate a square wave which repetitively
reverses the excitation polarity on the bridge. To
excite the bridge dynamically requires some type
of bridge driver external to the CS5516/CS5520
converter. This driver is driven by a square wave
clock. The source of this clock depends upon
whether the converter is set for internal excita-
tion or for external excitation. Figure 6
illustrates a sample bridge drive circuit when op-
erating in the internal AC excitation mode.
Using internal excitation involves setting the
EXC bit of the configuration register to 0, and
setting the F1 and F0 bits to select the excitation
frequency for the bridge. In this mode the exci-
tation frequency is a sub-multiple of the XIN
clock frequency. The excitation clock is output
22
+5V
0V
BX2
Figure 6. Sample AC Bridge Driver
+5V
10 k
10 k
100 k
TP0610
2
4
-5V
6
3
0.1 F
7
5
MICREL
MIC4428 or
MIC4425
EXC+
EXC-
-5V
+
10 F
+5V
+5V
-5V
-5V
from the BX1 and BX2 pins of the converter in
the form of a two-phase non-overlapping clock.
The converter is capable of demodulating this
clocked excitation. But only if the signals into
the AIN+ and VREF+ pins of the converter are
in phase with the demodulation clock inside the
converter (see Figure 7). The non-overlapping
clock signals from BX1 and BX2 are CMOS
level outputs (0 to VD+ volts) and are capable
of driving one TTL load. A buffer amplifier
MUST be used to drive the bridge.
Whenever the internal mode is used for dynamic
bridge excitation the signals are non-overlap-
ping. The non-overlapping time is one XIN
clock cycle.
The converter can also be configured to provide
dynamic bridge excitation when operating in the
external-controlled bridge excitation mode. With
the EXC bit of the configuration register set to
logic 1, the BX1 pin becomes an input which
determines the bridge excitation frequency and
phase. BX1 should be near 50% duty cycle. The
user can select the excitation frequency with the
following restrictions. The excitation frequency
must be synchronous with the XIN frequency of
the converter and must be chosen using the fol-
lowing equation:
where N is an integer and lies in the range in-
cluding 1 to 160. F
excitation frequency. Other asynchronous fre-
Figure 7. Internal Excitation Clock Phasing
Demod Clock
(Internal)
BX1 (Out)
BX2 (Out)
Note: The signals from the bridge into AIN+ and
F
VREF+ of the converter must be in phase
with the demodulation clock.
t
exc
d
is 1 cycle of XIN clock.
t
d
N XIN 81,920
exc
CS5516, CS5520
is the desired bridge
t
d
DS74F2
DS74F1