Datasheet

IN1
IN2
MICROPROCESSOR
DSP
SCLK
CS
DIN
DOUT
GND
V
A
ADC122S101
LP2950
5V
1 PF
TANT
0.1 PF 0.1 PF1 PF
| |
|
0V
+V
A
- 1.5LSB
0.5 LSB
ANALOG INPUT
1 LSB = V
A
/4096
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
ADC122S101
SNAS286D –MARCH 2005–REVISED MARCH 2013 www.ti.com
ADC122S101 TRANSFER FUNCTION
The output format of the ADC122S101 is straight binary. Code transitions occur midway between successive
integer LSB values. The LSB width for the ADC122S101 is V
A
/4096. The ideal transfer characteristic is shown in
Figure 51. 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 51. Ideal Transfer Characteristic
TYPICAL APPLICATION CIRCUIT
A typical application of the ADC122S101 is shown in Figure 52. Power is provided, in this example, by the
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 ADC122S101. Because the reference for
the ADC122S101 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 ADC122S101 supply pin. Because of the ADC122S101'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 52. Typical Application Circuit
ANALOG INPUTS
An equivalent circuit for one of the ADC122S101's input channels is shown in Figure 53. Diodes D1 and D2
provide ESD protection for the analog inputs. At no time should any input go beyond (V
A
+ 300 mV) or (GND −
300 mV), as these ESD diodes will begin conducting, which could result in erratic operation. For this reason,
these ESD diodes should NOT be used to clamp the input signal.
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