ADIS16204_07 AD [Analog Devices], ADIS16204_07 Datasheet - Page 11

• Manufacturer Part Number: ADIS16204_07
• Description: Programmable High-g Digital Impact Sensor and Recorder
• Manufacturer: AD [Analog Devices]

AUXILIARY ADC FUNCTION
The auxiliary ADC function integrates a standard 12-bit ADC
into the ADIS16204 to digitize other system-level analog sig-
nals. The output of the ADC can be monitored through the
AUX_ADC control register, as defined in Table 6. The ADC is
a 12-bit successive approximation converter. The output data
is presented in straight binary format with the full-scale range
extending from 0 V to V
calibrated 2.5 V reference is also provided.
Figure 20 shows the equivalent circuit of the analog input struc-
ture of the ADC. The input capacitor (C1) is typically 4 pF and
can be attributed to parasitic package capacitance. The two diodes
provide ESD protection for the analog input. Care must be
taken to ensure that the analog input signals never exceed the
supply rails by more than 300 mV. This causes the diodes to
become forward-biased and to start conducting. The diodes
can handle 10 mA without causing irreversible damage. The
resistor is a lumped component that represents the on resistance
of the switches. The value of this resistance is typically 100 Ω.
Capacitor C2 represents the ADC sampling capacitor and is
typically 16 pF.
REF
. A high precision, low drift, factory
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For ac applications, removing high frequency components from
the analog input signal is recommended by the use of a low-pass
filter on the analog input pin.
In applications where harmonic distortion and signal-to-noise
ratio are critical, the analog input must be driven from a low
impedance source. Large source impedances significantly affect
the ac performance of the ADC. This can necessitate the use of
an input buffer amplifier. When no input amplifier is used to drive
the analog input, the source impedance should be limited to
values lower than 1 kΩ.
Figure 20. Equivalent Analog Input Circuit
Conversion Phase: Switch Open
C1
Track Phase: Switch Closed
VDD
D
D
R1
C2
ADIS16204