Analog Devices ADXL180 iMEMS, Manual

Page: 43 / 56

ADXL180
Rev. 0 | Page 43 of 56
TEST AND DIAGNOSTIC TOOLS
V
SCI
SIGNAL CHAIN INPUT TEST PIN
The V
SCI
signal chain input test pin allows the excitation of the
signal chain from the input of the sensor interface circuitry
(sensor amplifier) through to the output of the current mode
serial port. The function of this pin becomes active after the pin
input voltage exceeds the level of about 0.8 V. Below this level,
the ADXL180 does not respond to the voltage applied to the
V
SCI
pin. Above the threshold limit of 0.8 V, the voltage signal at
the V
SCI
pin is applied to the sensor interface circuitry in parallel
with the sensor signal.
The applied signal is zero when the input signal is equal to the
common-mode potential of the sensor interface circuitry
(~V
DD
/2 V), see Figure 32. The V
SCI
input scaling for all ranges
is typically about 640 μV/ g . The scaling of the V
SCI
input voltage
to the ADC code output is dependent on the range setting of
the part.
+600
g
0
g
–600
g
0
754
4-
0
54
g
EQ
U
IVA
L
EN
T
~0.8 V
DD
/2 ~3.2
V
SCI
TEST PIN VOLTAGE
Figure 32. V
SCI
Signal Chain Input Test Pin Transfer Function
V
SCO
ANALOG SIGNAL CHAIN OUTPUT TEST PIN
The V
SCO
analog signal chain output test pin provides access to
the sensor signal chain analog output voltage at the output of
the Bessel filter. This signal is filtered and ranged as defined by
the configuration register settings. It is before the digital auto-
zero function in the signal chain. Therefore, it is not auto-
zeroed. The configuration register SCOE bit must be set to 1 to
enable this output. The signal output resistance is typically
50 Ω. Connect this output to a high impedance input only.
Table 40. SCOE V
SCO
Signal Chain Output Enable
SCOE Definition
0 V
SCO
output disabled. (Default.)
1 V
SCO
output enabled. Analog output prior to ADC
conversion is present on V
SCO
pin. Connect V
SCO
to high
impedance input, or data or sensor data may be
adversely affected.
Table 41. Typical V
SCO
Sensitivity Per g -Range
g -Range Sensitivity
50 g 32.8 mV/ g
100 g 16.4 mV/ g
150 g 10.8 mV/ g
200 g 8.2 mV/ g
250 g 6.56 mV/ g
350 g 4.69 mV/ g
500 g 3.28 mV/ g