MAX1402 Datasheet, PDF (25/40 Pages) Maxim Integrated Products – +5V, 18-Bit, Low-Power, Multichannel, Oversampling Sigma-Delta ADC

+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
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
PGA GAIN
1
2
4
8, 16, 32,
64, 128
C_EXT = 0pF
11.1
11.1
8.3
5.5
C_EXT = 50pF
4.9
4.9
4.2
EXTERNAL RESISTANCE R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
3.2
0.95
0.54
3.2
0.95
0.54
2.9
0.89
0.50
C_EXT = 5000pF
0.14
0.14
0.13
3.3
2.4
0.81
0.46
0.12
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
PGA GAIN
1
2
4
C_EXT = 0pF
5.4
5.4
4.0
C_EXT = 50pF
2.4
2.4
2.1
EXTERNAL RESISTANCE R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
1.6
0.47
0.26
1.6
0.47
0.26
1.4
0.43
0.25
C_EXT = 5000pF
0.069
0.069
0.064
8, 16, 32,
64, 128
2.7
1.6
1.2
0.39
0.23
0.059
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-,
R_EXT
C_EXT
R_MUX
R_IN
C_PIN
C_ST
C_AMP
C_SAMPLE
C_C
Figure 6. Analog Input, Buffered Mode (BUFF = 1)
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