Rainbow-electronics MAX1402 Bedienungsanleitung PDF herunterladen (Seite 25)

MAX1402

+5V, 18-Bit, Low-Power, Multichannel,

Oversampling (Sigma-Delta) ADC

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Input Buffers

The MAX1402 provides a pair of input buffers to isolate

the inputs from the capacitive load presented by the

PGA/modulator (Figure 6). The buffers are chopper sta-

bilized to reduce the effect of their DC offsets and low-

frequency noise. Since the buffers can represent more

than 50% of the total analog power dissipation, they may

be shut down in applications where minimum power dis-

sipation is required and the capacitive input load is not a

concern. Disable the buffers in applications where the

inputs must operate close to AGND or V+.

When used in buffered mode, the buffers isolate the

inputs from the sampling capacitors. The sampling-

related gain error is dramatically reduced in this mode.

A small dynamic load remains from the chopper stabi-

lization. The multiplexer exhibits a small input leakage

current of up to 10nA. With high source resistances,

this leakage current may result in a DC offset.

Reference Input

The MAX1402 is optimized for ratiometric measure-

ments and includes a fully differential reference input.

Apply the reference voltage across REFIN+ and REFIN-,

Table 13c. R

EXT

, C

EXT

Values for Less than 16-Bit Gain Error in Unbuffered (BUFF = 0)

Mode—4x Modulator Sampling Frequency (MF1, MF0 = 10 ); X2CLK = 0; CLKIN =

2.4576MHz

Table 13d. R

EXT

, C

EXT

Values for Less than 16-Bit Gain Error in Unbuffered (BUFF = 0)

Mode—8x Modulator Sampling Frequency (MF1, MF0 = 11); X2CLK = 0; CLKIN =

2.4576MHz

EXT

MUX

AMP

SAMPLE

Figure 6. Analog Input, Buffered Mode (BUFF = 1)

11.1 4.9

11.1 4.9 3.22

8.3 4.2

5.5 3.3 2.4

8, 16, 32,

64, 128

2.9

3.2

EXT

= 0pF C

EXT

= 50pF C

EXT

= 100pF

0.95 0.54

0.95 0.54 0.14

0.89 0.50

0.81 0.46 0.12

0.13

PGA GAIN

0.14

EXT

= 500pF C

EXT

= 1000pF C

EXT

= 5000pF

EXTERNAL RESISTANCE R

EXT

(kΩ)

5.4 2.4

5.4 2.4 1.62

4.0 2.1

2.7 1.6 1.2

8, 16, 32,

64, 128

1.4

1.6

EXT

= 0pF C

EXT

= 50pF C

EXT

= 100pF

0.47 0.26

0.47 0.26 0.069

0.43 0.25

0.39 0.23 0.059

0.064

PGA GAIN

0.069

EXT

= 500pF C

EXT

= 1000pF C

EXT

= 5000pF

EXTERNAL RESISTANCE R

EXT

(kΩ)

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 39 40

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