ADS1282IPWR datasheet(13/52 Pages) TI

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INPUT-REFERRED NOISE

SNR=20log

FSR

RMS

(1)

IDLE TONES

NOISE PERFORMANCE

OPERATING MODE

ADS1282

www.ti.com ........................................................................................................................................ SBAS418E – SEPTEMBER 2007 – REVISED OCTOBER 2008

The device features unipolar and bipolar analog

power supplies (AVDD and AVSS, respectively) for

The input-referred noise is related to SNR by

input range flexibility and a digital supply accepting

Equation 1:

1.8V to 3.3V. The analog supplies may be set to +5V

to accept unipolar signals (with input offset) or set

lower in the range of ±2.5V to accept true bipolar

input signals (ground referenced).

where:

An internal sub-regulator is used to supply the digital

core from DVDD. The BYPAS pin (pin 28) is the

FSRRMS = Full-scale range RMS = VREF/2 × √2 ×

sub-regulator output and requires a 1

µF capacitor for

PGA

noise reduction. BYPAS should not be used to drive

NRMS = Noise RMS (input-referred)

external circuitry.

The ADS1282 modulator incorporates an internal

The ADS1282 offers outstanding noise performance

dither signal that randomizes the idle tone energy.

(SNR). SNR depends on the data rate, the PGA

Low-level idle tones may still be present, typically

setting, and the mode (high-resolution or low-power).

–137dB below full-scale. The low-level idle tones can

As the bandwidth is reduced by decreasing the data

be shifted out of the passband with an external offset

rate, the SNR improves correspondingly. Similarly, as

= 20mV/PGA. See the Application Information section

the PGA gain is increased, the SNR decreases. In

for the recommended offset circuit.

low-power mode, the SNR decreases 3dB for each

setting. Table 1 summarizes the noise performance

versus data rate, PGA setting, and mode.

For applications where minimal power consumption is

important, the low-power mode can be selected

(register bit MODE = 0). In low-power mode, the

power is reduced to 17mW (from 25mW) and SNR

decreases an average of 3dB. The default mode is

high-resolution.

Table 1. Signal-to-Noise Ratio (dB)(1)

PGA (High-Resolution Mode)

PGA (Low-Power Mode)

DATA RATE

(SPS)

250

130

129

128

125

119

114

127

126

125

122

116

111

500

127

126

125

122

116

111

124

123

122

119

113

108

1000

124

123

122

119

113

108

121

120

119

116

110

105

2000

121

120

119

116

111

106

118

117

116

113

108

103

4000

118

117

116

113

108

103

115

114

113

110

105

100

(1)

VIN = 20mVDC/PGA.

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