cs5520-bp Cirrus Logic, Inc., cs5520-bp Datasheet - Page 17

• Manufacturer Part Number: cs5520-bp
• Description: 16/20-bit Bridge Transducer A/d Converters
• Manufacturer: Cirrus Logic, Inc.

bits can be manipulated by the user to add or
subtract offset up to 200 percent of the nominal
input signal. The AIN ratiometric offset register
can be manipulated to add or subtract offset
equal to the maximum differential input signal
into the X25 amplifier. An LSB in the ratiomet-
ric offset register represents 2
the voltage input across the VREF+ and VREF-
pins at the internal input to the AIN channel
A/D converter. This will be scaled down by the
AIN channel gain when calculated relative to the
instrumentation amplifier input. For example,
with a VREF = 2.5 V, the PGA gain = 1, one
count of the ratiometric offset register would
represent about 12 nV at the instrumentation am-
plifier input. The proportion remains ratiometric
even if the VREF voltage should change. The
24-bit register content is stored in 2’s comple-
ment form.
Manipulation of the DAC or ratiometric offset
register allows the user to shift the transfer func-
tion to allow for load cell creep or load cell zero
drift.
The gain calibration is performed last. The con-
tents of the gain register spans from 2
shown in Table 4. After gain calibration has
been performed, the numeric value in the gain
register should not exceed the range of 0.8 to
1.2. The gain calibration range is
nominal value of 1.0. The nominal value of 1.0
is for an input span dictated by the VREF volt-
age, the PGA gain, and the X25 instrumentation
gain. The converter may operate with gain slope
factors from 0.5 to 2.0 (decimal), but when the
slope exceeds 1.2 the converter output code
computation may lack adequate resolution and
result in missing codes in the transfer function.
Internal circuitry may saturate for large signals
which would calibrate to a gain factor less than
0.8.
DS74F1
DS74F2
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proportion of
20 % of the
-23
to 2 as
In a typical weigh scale application, the
CS5516/CS5520 will be calibrated in combina-
tion with a load cell at the factory. Once
calibrated, the calibration words are off-loaded
from the converter and stored in E
When powered-up in the field the calibration
words are up-loaded into the appropriate regis-
ters. This is viable because the AIN and VREF
input to the converter are "chopper-stabilized"
and maintain excellent stability when subjected
to changes in temperature.
Programmable Gain Amplifier
The programmable gain amplifier inside the
CS5516/20 offers gains of 1, 2, 4, and 8. This is
in addition to the fixed gain of
instrumentation amplifier. The gain tracking of
the PGA is about one percent between ranges.
The user can remove this error by performing a
gain calibration at the factory with a full scale
signal on each range. The gain calibration word
for each gain range can be off-loaded into
E
whenever a new gain setting is selected for the
PGA. Gain stability over temperature for the
converter itself is approximately 1 ppm/ C when
the device is used ratiometrically.
Serial Interface Modes
The CS5516/20 support either 5, 4 or 3 pin se-
rial interfacing. The SMODE pin sets the
operating mode of the serial interface. With
SMODE = 0, the device assumes the user is op-
erating with either a 5 or 4 wire interface. The
five wire mode includes SOD, SID, SCLK,
DRDY, and CS. In the four wire mode, CS is
connected to DGND as a logic 0. The user
would then interface to the SOD, SID, SCLK,
and DRDY pins.
2
PROM and uploaded into the gain register
CS5516, CS5520
25 in the input
2
PROM.
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