Datasheet

MAX1020/MAX1022/MAX1057/MAX1058
10-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
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Unipolar or Bipolar Conversions
Address the unipolar- and bipolar-mode registers
through the setup register (bits 1 and 0). See Table 5 for
the setup register. See Figures 3 and 4 for the transfer-
function graphs. Program a pair of analog inputs for dif-
ferential operation by writing a one to the appropriate bit
of the bipolar- or unipolar-mode register. Unipolar mode
sets the differential input range from 0 to V
REF1.
A nega-
tive differential analog input in unipolar mode causes the
digital output code to be zero. Selecting bipolar mode
sets the differential input range to ±V
REF1
/ 2. The digital
output code is binary in unipolar mode and two’s com-
plement in bipolar mode.
In single-ended mode, the MAX1020/MAX1022/
MAX1057/MAX1058 always operate in unipolar mode.
The analog inputs are internally referenced to AGND
with a full-scale input range from 0 to the selected refer-
ence voltage.
Analog Input (T/H)
The equivalent circuit of Figure 2 shows the ADC input
architecture of the MAX1020/MAX1022/MAX1057/
MAX1058. In track mode, a positive input capacitor is
connected to AIN0–AIN15 in single-ended mode and
AIN0, AIN2, and AIN4–AIN14 (only positive inputs) in
differential mode. A negative input capacitor is con-
nected to AGND in single-ended mode or AIN1, AIN3,
and AIN5–AIN15 (only negative inputs) in differential
mode. For external T/H timing, use clock mode 01. After
the T/H enters hold mode, the difference between the
sampled positive and negative input voltages is con-
verted. The input capacitance charging rate determines
the time required for the T/H to acquire an input signal.
If the input signal’s source impedance is high, the
required acquisition time lengthens.
Any source impedance below 300Ω does not signifi-
cantly affect the ADC’s AC performance. A high-imped-
ance source can be accommodated either by
lengthening t
ACQ
(only in clock mode 01) or by placing
a 1µF capacitor between the positive and negative ana-
log inputs. The combination of the analog-input source
impedance and the capacitance at the analog input cre-
ates an RC filter that limits the analog input bandwidth.
Input Bandwidth
The ADC’s input-tracking circuitry has a 1MHz small-
signal bandwidth, making it is possible to digitize high-
speed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. Anti-alias prefiltering
of the input signals is necessary to avoid high-frequen-
cy signals aliasing into the frequency band of interest.
Analog-Input Protection
Internal electrostatic-discharge (ESD) protection diodes
clamp all analog inputs to AVDD and AGND, allowing
the inputs to swing from (V
AGND
- 0.3V) to (V
AVDD
+
0.3V) without damage. However, for accurate conver-
sions near full scale, the inputs must not exceed V
AVDD
by more than 50mV or be lower than AGND by 50mV. If
an analog input voltage exceeds the supplies, limit the
input current to 2mA.
Internal FIFO
The MAX1020/MAX1022/MAX1057/MAX1058 contain a
first-in/first-out (FIFO) buffer that holds up to 16 ADC
results plus one temperature result. The internal FIFO
allows the ADC to process and store multiple internally
clocked conversions and a temperature measurement
without being serviced by the serial bus.
If the FIFO is filled and further conversions are request-
ed without reading from the FIFO, the oldest ADC
results are overwritten by the new ADC results. Each
result contains 2 bytes, with the MSB preceded by four
leading zeros and the LSB followed by 2 sub-bits. After
each falling edge of CS, the oldest available pair of
bytes of data is available at DOUT, MSB first. When the
FIFO is empty, DOUT is zero.
AIN0–AIN15
(SINGLE-ENDED),
AIN0, AIN2,
AIN4–AIN14
(DIFFERENTIAL)
COMPARATOR
HOLD
ACQ
ACQ
HOLD
ACQ
HOLD
AVDD/2
REF1
AGND
CIN+
CIN-
DAC
AGND
(SINGLE-ENDED),
AIN1, AIN3,
AIN5–AIN15
(DIFFERENTIAL)
Figure 2. Equivalent Input Circuit