ADIS16204 Просмотр технического описания (PDF) - Analog Devices

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ADIS16204

Programmable High-g Digital Impact Sensor and Recorder

Analog Devices 

ADIS16204

AUXILIARY ADC FUNCTION

VDD

The auxiliary ADC function integrates a standard 12-bit ADC

D

R1 C2

into the ADIS16204 to digitize other system-level analog sig-

nals. The output of the ADC can be monitored through the

C1

D

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

Figure 20. Equivalent Analog Input Circuit

Conversion Phase: Switch Open

Track Phase: Switch Closed

extending from 0 V to VREF. A high precision, low drift, factory

calibrated 2.5 V reference is also provided.

For ac applications, removing high frequency components from

the analog input signal is recommended by the use of a low-pass

Figure 20 shows the equivalent circuit of the analog input struc-

filter on the analog input pin.

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

E 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.

T Capacitor C2 represents the ADC sampling capacitor and is

OBSOLE typically 16 pF.

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.

Rev. B | Page 11 of 24

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