MAX1400 Maxim, MAX1400 Datasheet - Page 22

• Manufacturer Part Number: MAX1400
• Description: %V / 18-Bit / Low-Power / Multichannel / Oversampling Sigma-Delta ADC
• Manufacturer: Maxim

+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Table 13c. R
Mode—4x Modulator Sampling Frequency (MF1, MF0 = 10 ); X2CLK = 0; f
2.4576MHz
Table 13d. R
Mode—8x Modulator Sampling Frequency (MF1, MF0 = 11); X2CLK = 0; f
2.4576MHz
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
Figure 6. Analog Input, Buffered Mode (BUFF = 1)
22
PGA GAIN
PGA GAIN
8, 16, 32,
8, 16, 32,
______________________________________________________________________________________
64, 128
64, 128
1
2
4
1
2
4
R
EXT
EXT
EXT
C
EXT
C
C
, C
EXT
EXT
, C
9.3
9.3
7.2
5.0
4.5
4.5
3.5
2.4
EXT
EXT
= 0pF
= 0pF
C
Values for Less than 16-Bit Gain Error in Unbuffered (BUFF = 0)
Values for Less than 16-Bit Gain Error in Unbuffered (BUFF = 0)
PIN
R
MUX
C
C
MUXOUT
EXT
EXT
4.5
4.5
3.9
3.1
2.2
2.2
1.9
1.5
= 50pF
= 50pF
Input Buffers
C
ST
C
PIN
ADCIN
EXTERNAL RESISTANCE R
EXTERNAL RESISTANCE R
C
C
EXT
EXT
3.0
3.0
2.7
2.3
1.5
1.5
1.3
1.1
R
= 100pF
= 100pF
IN
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.
C
AMP
C
C
EXT
EXT
0.94
0.94
0.87
0.79
0.46
0.46
0.42
0.38
= 500pF
= 500pF
EXT
EXT
(kΩ)
(kΩ)
C
C
C
EXT
EXT
SAMPLE
0.53
0.53
0.50
0.45
0.26
0.26
0.24
0.22
= 1000pF
= 1000pF
CLKIN
CLKIN
C
C
EXT
EXT
=
C
=
C
0.069
0.069
0.069
0.059
0.14
0.14
0.13
0.12
= 5000pF
= 5000pF