CDB5378 Cirrus Logic Inc, CDB5378 Datasheet - Page 30

• Manufacturer Part Number: CDB5378
• Description: EVALUATION BOARD FOR CS5378
• Manufacturer: Cirrus Logic Inc

Specifications of CDB5378

• Main Purpose: Seismic Evaluation System
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: CS3301A, CS5373A, CS5378
• Primary Attributes: Single Digital Filter
• Secondary Attributes: Graphical User Interface, SPI™ & USB Interfaces
• Processor To Be Evaluated: CS5378
• Interface Type: USB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

tests and two external differential inputs. One
external input is typically dedicated to sensor
measurements and the other to testing the
electronics channel.
The OUT± outputs are enabled in all opera-
tional
(MODE 0), “AC BUF Only” mode (MODE 3)
and sleep mode (MODE 7). In modulator
mode, AC BUF Only mode and sleep mode
the OUT± pins are high impedance.
7.4 DAC BUF± Buffered Output
The test DAC BUF± pins are buffered differen-
tial analog outputs for testing external sensors
such as geophones or hydrophones. The buff-
ered outputs have reduced performance spec-
ifications compared with the OUT± outputs,
but are less sensitive to external loading.
The BUF± outputs are enabled in all operation-
al modes except modulator mode (MODE 0),
“AC OUT Only” mode (MODE 2) and sleep
mode
AC OUT only and sleep mode the BUF± pins
are high impedance to ensure they do not in-
terfere with sensor operation during normal
data acquisition.
For sensor impedance testing, it is required to
place matched series resistors in between the
BUF± outputs and the differential sensor. With
known series resistors and a known DC differ-
ential source voltage, sensor resistance can
be calculated ratiometrically from the mea-
sured voltage drop across the sensor.
7.5 DAC CAP± Connection
The CS5373A test DAC requires a 10 nF C0G
type capacitor to be connected differentially
across the CAP± pins. This capacitor creates
an internal anti-alias filter to eliminate high-fre-
30
modes
(MODE 7).
except
In
modulator
modulator
mode,
mode
quency signals from the OUT± and BUF± ana-
log outputs and helps to maintain the stability
of the low-power ΔΣ DAC circuitry.
A COG, NPO or similar high-quality capacitor
is required for CAP
types, such as X7R, do not have the required
linearity. Using a poor-quality capacitor on
CAP± will significantly degrade THD perfor-
mance of the test DAC AC operational modes.
7.6 Analog Differential Signals
Differential AC test signals into and out of the
CS5373A consist of two halves with equal but
opposite magnitude varying about a common
mode voltage. A full-scale 5 V
AC signal centered on a -0.15 V common
mode voltage will have:
For the opposite case:
So the total swing for SIG+ relative to SIG- is
(+2.5 V) - (-2.5 V) = 5 V
calculation can be done for SIG- relative to
SIG+. It’s important to note that a 5 V
ential signal centered on a -0.15 V common
mode voltage never exceeds +1.1 V with re-
spect to ground and never drops below -1.4 V
with respect to ground on either half. By defini-
tion, differential voltages are measured with
respect to the opposite half, not relative to
ground. A voltmeter differentially measuring
between SIG+ and SIG- in the above example
would correctly read 1.767 V
SIG+ = -0.15 V + 1.25 V = +1.1 V
SIG- = -0.15 V - 1.25 V = -1.4 V
SIG+ is +2.5 V relative to SIG-
SIG+ = -0.15 V - 1.25 V = -1.4 V
SIG- = -0.15 V + 1.25 V = +1.1 V
SIG+ is -2.5 V relative to SIG-
±
pp
since other capacitor
differential. A similar
rms
, or 5 V
PP
CS5373A
differential
pp
DS703F2
pp
differ-
.