MAX11156 Datasheet, PDF (11/27 Pages) Maxim Integrated Products – 18-Bit, 500ksps, ±5V SAR ADC with Internal Reference in TDFN

MAX11156
Functional Diagram
AIN+
AIN-
AGNDS
18-BIT ADC
MAX11156
INTERFACE
AND CONTROL
CONFIGURATION REGISTER
REFIO
SW1
INTERNAL
REFERENCE
10kΩ
SW2
REF
BUF
18-Bit, 500ksps, ±5V SAR ADC
with Internal Reference in TDFN
DIN
SCLK
DOUT
CNVST
V_DD
OVDD
GND
REF
CONFIGURATION
REGISTER
B5
B4
0
0
0
1
1
0
1
1
REFERENCE SWITCH
REFERENCE
STATE
MODE
SW2
SW1
0
CLOSED CLOSED
1
CLOSED OPEN
2
OPEN CLOSED
3
OPEN OPEN
Detailed Description
The MAX11156 is an 18-bit single-channel, pseudo-differ-
ential ADC with a maximum throughput rates of 500ksps.
This ADC includes a precision internal reference that
allows for measuring a bipolar input voltage range of Q5V.
An external reference can also be applied for input ranges
between Q3.05V and Q5.19V. Both inputs (AIN+ and AIN-)
are sampled with a pseudo-differential on-chip track-and-
hold exhibiting no pipeline delay or latency, making these
ADCs ideal for multiplexed applications.
The MAX11156 measures a true bipolar voltage of Q5V
(10V_P-P) and the inputs are protected for up to Q20mA of
overrange current. This ADC is powered from a 4.75V to
5.25V analog supply (V_DD) and a separate 2.3V to 5.25V
digital supply (OVDD). The MAX11156 requires 500ns to
acquire the input sample on an internal track-and-hold
and then convert the sampled signal to 18 bits of accuracy
using an internally clocked converter.
Analog Inputs
The MAX11156 ADC consists of a true sampling pseudo-
differential input stage with high-impedance, capacitive
inputs. The internal T/H circuitry feature a small-signal
bandwidth of about 6MHz to provide 18-bit accurate
sampling in 500ns. This allows for accurate sampling of
a number of scanned channels through an external mul-
tiplexer.
The MAX11156 can thus convert input signals on AIN+ in
the range of -(K O V_REF + AIN-) to +(K O V_REF + AIN-)
where K = 5.000/4.096. AIN+ should also be limited to
±(V_DD + 0.1V) for accurate conversions. AIN- has an
input range of -0.1V to +0.1V and should be connected
to the ground reference of the input signal source. The
MAX11156 performs a true differential sample on inputs
between AIN+ and AIN- with good common-mode rejec-
tion (see the Typical Operating Circuit). This allows for
improved sampling of remote transducer inputs.
Many traditional ADCs with single supplies that mea-
sure bipolar input signals use resistive divider networks
directly on the analog inputs. These networks increase
the complexity of the input signal conditioning. However,
the MAX11156 includes a patented input switch architec-
ture which allows direct sampling onto the input sample
and hold capacitor without the use of scaling resistor net-
works. This results in zero source loading errors when the
sample and hold is allowed to fully settle. This architec-
ture requires a minimum sample rate of 10Hz to maintain
accurate conversions over the designed temperature and
supply ranges.
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