Table 13c. r – Rainbow Electronics MAX1402 User Manual
Page 25
MAX1402
+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
______________________________________________________________________________________
25
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
R
EXT
C
EXT
R
MUX
C
PIN
R
IN
C
ST
C
AMP
C
SAMPLE
C
C
Figure 6. Analog Input, Buffered Mode (BUFF = 1)
11.1
4.9
11.1
4.9
3.2
2
8.3
4.2
5.5
3.3
2.4
8, 16, 32,
64, 128
2.9
3.2
4
1
C
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
C
EXT
= 500pF
C
EXT
= 1000pF
C
EXT
= 5000pF
EXTERNAL RESISTANCE R
EXT
(k
Ω
)
5.4
2.4
5.4
2.4
1.6
2
4.0
2.1
2.7
1.6
1.2
8, 16, 32,
64, 128
1.4
1.6
4
1
C
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
C
EXT
= 500pF
C
EXT
= 1000pF
C
EXT
= 5000pF
EXTERNAL RESISTANCE R
EXT
(k
Ω
)