Datasheet

IN1
IN2
MICROPROCESSOR
DSP
SCLK
CS
DIN
DOUT
GND
V
A
ADC084S021
LP2950
5V
1 PF
0.1 PF 0.1 PF1 PF
IN3
IN4
| |
|
0V
+V
A
- 1 LSB
½ LSB
ANALOG INPUT
1LSB = V
A
/256
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
ADC084S021
SNAS279E –APRIL 2005–REVISED MARCH 2013 www.ti.com
Figure 48. Ideal Transfer Characteristic
TYPICAL APPLICATION CIRCUIT
A typical application of the ADC084S021 is shown in Figure 50. 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 ADC084S021.
Because the reference for the ADC084S021 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 ADC084S021 supply pin. Because of the
ADC084S021'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 also shown connected to a microprocessor or DSP.
Figure 49. Typical Application Circuit
ANALOG INPUTS
An equivalent circuit for one of the ADC084S021's input channels is shown in Figure 50. 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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