MAX11166 Datasheet, PDF (19/33 Pages) Maxim Integrated Products – 16-Bit, 500ksps/250ksps, ±5V SAR ADCs with Internal Reference in TDFN

MAX11166/MAX11167
16-Bit, 500ksps/250ksps, ±5V SAR ADCs
with Internal Reference in TDFN
Reference Mode 11: The internal bandgap reference
source as well as the internal reference buffer are both
in a shutdown state. The REF pin is in a high-impedance
state. This mode would typically be used when an exter-
nal reference source and external reference buffer is used
to drive all MAX11166/MAX11167 parts in a system.
Regardless of the reference mode used, the MAX11166/
MAX11167 require a low-impedance reference source on
the REF pin to support 16-bit accuracy. When using the
internal reference buffer, externally bypass the reference
buffer output using at least a 10FF, low-inductance, low-
ESR capacitor placed as close as possible to the REF pin,
thus minimizing additional PCB inductance. When using
the internal bandgap reference source, bypass the REFIO
pin with a 0.1FF capacitor to ground. If providing an exter-
nal reference and using the internal reference buffer, drive
the REFIO pin directly with an external reference source
in the range of 3.0V to 4.25V. Finally, if disabling the
MAX11166/MAX11167 internal bandgap reference source
and internal reference buffer, drive the REF pin with a ref-
erence voltage in the range of 2.5V to 4.25V and place at
least a 10FF, low-inductance, low-ESR capacitor placed
as close as possible to the REF pin .
When using the MAX11166/MAX11167 in external refer-
ence mode, it is recommended that an external reference
buffer be used. For bypass capacitors on the REF pin,
X7R or X5R ceramic capacitors in a 1210 case size or
smaller have been found to provide adequate bypass
performance. Y5U or Z5U ceramics capacitors are not
recommended due to their high voltage and temperature
coefficients.
Maxim offers a wide range of precision references ideal
for 16-bit accuracy. Table 1 lists some of the options rec-
ommended.
Input Amplifier
The conversion results are accurate when the ADC
acquires the input signal for an interval longer than the
input signal's worst-case settling time. The ADC input
sampling capacitor charges during the acquisition period.
During this acquisition period, the settling of the sampled
voltage is affected by the source resistance and the input
sampling capacitance. Sampling error can be estimated
by modeling the time constant of the total input capaci-
tance and the driving source impedance.
Although the MAX11166/MAX11167 are easy to drive, an
amplifier buffer is recommended if the source impedance
is such that when driving a switch capacitor of ~20pF a
significant settling error in the desired sampling period will
occur. If this is the case, it is recommended that a con-
figuration shown in the Typical Operating Circuit is used
where at least a 500pF capacitor is attached to the AIN+
pin. This capacitance reduces the size of the transient at
the start of the acquisition period, which in some buffers
will cause an input signal dependent offsets.
Regardless of whether an external buffer amp is used or
not, the time constant, R_SOURCE × C_LOAD, of the input
should not exceed t_ACQ/12, where R_SOURCE is the total
signal source impedance, C_LOAD is the total capacitance
at the ADC input (external and internal) and t_ACQ is the
acquisition period. Thus to obtain accurate sampling in a
500ns acquisition time a source impedance of less than
1042Ω should be used if driving the ADC directly. When
driving the ADC from a buffer, it is recommended a series
resistance (5Ω to 50Ω typical) between the amplifier and
the external input capacitance as shown in the Typical
Operating Circuit.
1) Fast settling time: For multichannel multiplexed appli-
cations the driving operational amplifier must be able
to settle to 16-bit resolution when a full-scale step is
applied during the minimum acquisition time.
2) Low noise: It is important to ensure that the driver
amplifier has a low average noise density appropriate
for the desired bandwidth of the application. When
the MAX11166/MAX11167 are used with its full band-
width of 6MHz, it is preferable to use an amplifier that
will produce an output noise spectral density of less
than 6nV/√Hz, to ensure that the overall SNR is not
Table 1. MAX11166/MAX11167 External Reference Recommendations
PART
MAX6126
MAX6325
MAX6341
MAX6350
V_OUT (V)
2.5, 3, 4.096, 5.0
TEMPERATURE
COEFFICIENT (MAX)
3 (A), 5 (B)
INITIAL
ACCURACY (%)
0.06
NOISE (0.1Hz TO
10Hz) (µV_P-P)
1.35
2.5, 4.096, 5.0
1
0.04, 0.02
1.5, 2.4, 3.0
PACKAGE
µMAX-8
SO-8
SO-8
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