Datasheet

IN2
MICROPROCESSOR
DSP
SCLK
CS
DIN
DOUT
GND
V
A
ADC122S021
LP2950
5V
1 PF
TANT
0.1 PF 0.1 PF1 PF
IN1
| |
|
0V
+V
A
- 1.5LSB
0.5LSB
ANALOG INPUT
1LSB = V
A
/4096
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
ADC122S021
SNAS280D –MARCH 2005–REVISED MARCH 2013 www.ti.com
ADC122S021 TRANSFER FUNCTION
The output format of the ADC122S021 is straight binary. Code transitions occur midway between successive
integer LSB values. The LSB width for the ADC122S021 is V
A
/4096. The ideal transfer characteristic is shown in
Figure 47. The transition from an output code of 0000 0000 0000 to a code of 0000 0000 0001 is at 1/2 LSB, or a
voltage of V
A
/8192. Other code transitions occur at steps of one LSB.
Figure 47. Ideal Transfer Characteristic
TYPICAL APPLICATION CIRCUIT
A typical application of the ADC122S021 is shown in Figure 48. Power is provided, in this example, by the Texas
Instruments LP2950 low-dropout voltage regulator, available in a variety of fixed and adjustable output voltages.
The power supply pin is bypassed with a capacitor network located close to the ADC122S021. Because the
reference for the ADC122S021 is the supply voltage, any noise on the supply will degrade device noise
performance. To keep noise off the supply, use a dedicated linear regulator for this device, or provide sufficient
decoupling from other circuitry to keep noise off the ADC122S021 supply pin. Because of the ADC122S021's low
power requirements, it is also possible to use a precision reference as a power supply to maximize performance.
The four-wire interface is shown connected to a microprocessor or DSP.
Figure 48. Typical Application Circuit
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