MAX1400_02 Datasheet, PDF (22/34 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; f_CLKIN =
2.4576MHz
PGA GAIN
1
2
4
8, 16, 32,
64, 128
C_EXT = 0pF
9.3
9.3
7.2
5.0
C_EXT = 50pF
4.5
4.5
3.9
EXTERNAL RESISTANCE R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
3.0
0.94
0.53
3.0
0.94
0.53
2.7
0.87
0.50
C_EXT = 5000pF
0.14
0.14
0.13
3.1
2.3
0.79
0.45
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; f_CLKIN =
2.4576MHz
PGA GAIN
1
2
4
8, 16, 32,
64, 128
C_EXT = 0pF
4.5
4.5
3.5
2.4
C_EXT = 50pF
2.2
2.2
1.9
EXTERNAL RESISTANCE R_EXT (kΩ)
C_EXT = 100pF C_EXT = 500pF C_EXT = 1000pF
1.5
0.46
0.26
1.5
0.46
0.26
1.3
0.42
0.24
C_EXT = 5000pF
0.069
0.069
0.069
1.5
1.1
0.38
0.22
0.059
Input Buffers
The MAX1400 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 dissipation 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 MUXOUT}
ADCIN ^RIN
C_PIN
C_ST C_PIN
C_AMP
C_SAMPLE
C_C
Figure 6. Analog Input, Buffered Mode (BUFF = 1)
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