MAX11156 Datasheet, PDF (14/27 Pages) Maxim Integrated Products – 18-Bit, 500ksps, ±5V SAR ADC with Internal Reference in TDFN

MAX11156
18-Bit, 500ksps, ±5V SAR ADC
with Internal Reference in TDFN
is preferable to use an amplifier that will produce an
output noise spectral density of less than 6nV/√Hz, to
ensure the overall SNR is not degraded significantly.
It is recommended to insert an external RC filter at
the MAX11156 AIN+ input to attenuate out-of-band
input noise and preserve the ADC's SNR. The effec-
tive RMS noise at the MAX11156 AIN+ input is 65FV,
thus additional noise from a buffer circuit should be
significantly lower in order to achieve the maximum
SNR performance.
3) THD performance: The input buffer amplifier used
should have a comparable THD performance with that
of the MAX11156 to ensure the THD of the digitized
signal is not degraded.
Table 2 summarizes the operational amplifiers that are
compatible with the MAX11156. The MAX9632 has suf-
ficient bandwidth, low enough noise and distortion to sup-
port the full performance of the MAX11156. The MAX9633
is a dual amp and can support buffering for true pseudo-
differential sampling.
Transfer Function
The ideal transfer characteristic for the MAX11156 is
shown in Figure 3. The precise location of various points
on the transfer function are given in Table 3.
3FFFF
3FFFE
20001
20000
+FS
=
5
x V_REF
4.096
-FS
=
-5 x V_REF
4.096
LSB =+F2S62-1(4-F4S)
TRANSITION
1FFFF
1FFFE
00001
00000
-FS
-FS + 0.5 × LSB
0
+FS - 1.5 × LSB
INPUT VOLTAGE (LSB)
Figure 3. Bipolar Transfer Function
Table 2. List of Recommended ADC Driver Op Amps for MAX11156
+FS - 1LSB
+FS
AMPLIFIER
MAX9632
MAX9633
INPUT-NOISE
DENSITY
(nV/√Hz)
1
3
SMALL-SIGNAL
BANDWIDTH
(MHz)
55
27
SLEW RATE
(V/µs)
30
18
THD
(dB)
-128
-128
I_CC
(mA)
COMMENTS
3.9 Single amp, low noise, low THD
3.5 Dual amp, low noise, low THD
Table 3. Transfer Function Example
CODE TRANSITION
+FS - 1.5 LSB
Midscale + 0.5 LSB
Midscale
Midscale - 0.5 LSB
-FS + 0.5 LSB
BIPOLAR INPUT (V)
+4.999943
+0.000019
0
-0.000019
-4.999981
DIGITAL OUTPUT CODE (HEX)
3FFFE - 3FFFF
20000 - 20001
20000
1FFFF - 20000
00000 - 00001
www.maximintegrated.com
Maxim Integrated │  14