MAX1403 Datasheet, PDF (24/36 Pages) Maxim Integrated Products – +3V, 18-Bit, Low-Power, Multichannel, Oversampling Sigma-Delta ADC

+3V, 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
C_EXT = 0pF
8.3
8.3
6.2
C_EXT = 50pF
3.7
3.7
3.2
EXTERNAL RESISTANCE, R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
2.4
0.72
0.40
2.4
0.72
0.40
2.2
0.67
0.38
C_EXT = 5000pF
0.11
0.11
0.10
8, 16, 32,
64, 128
4.1
2.5
1.8
0.60
0.35
0.09
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
8, 16, 32,
64, 128
C_EXT = 0pF
4.1
4.1
3.0
2.0
C_EXT = 50pF
1.8
1.8
1.5
EXTERNAL RESISTANCE, R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
1.2
0.35
0.20
1.2
0.35
0.20
1.1
0.32
0.18
C_EXT = 5000pF
0.05
0.05
0.05
1.2
0.88
0.29
0.17
0.04
Input Buffers
The MAX1403 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.
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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