Datasheet

MAX1377/MAX1379/MAX1383
Dual, 12-Bit, 1.25Msps Simultaneous-Sampling
ADCs with Serial Interface
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the MAX1383, the signal bandwidth is limited to 100kHz
by specification. Since ±10V signals are divided down to
a 2.5V range, this version should only be used with sig-
nals greater than 5V. For those applications with signals
5V or less, use the MAX1377/MAX1379 for best SNR per-
formance. The configuration is shown on Figure 3b.
Input Bandwidth
The ADC’s input-tracking circuitry has a 5MHz small-
signal bandwidth, allowing the ADC to digitize high-
speed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. To avoid high-fre-
quency signals being aliased into the frequency band
of interest, anti-alias filtering is recommended.
Analog Input Protection
Internal protection diodes that clamp the analog input
to AVDD and AGND allow the analog inputs to swing
from AGND - 0.3V to AVDD + 0.3V without damage to
the MAX1377 and MAX1379. The MAX1383 can handle
±10V input swings. All inputs must not exceed the stat-
ed ranges for accurate conversions.
Internal Reference Mode
Drive REFSEL low to select internal reference mode. The
MAX1377 includes an on-chip 2.048V reference; the
MAX1379 has a 4.096V reference; and the MAX1383
includes a 2.5V internal reference. The reference output
at REF can be used as a reference voltage source for
other components. REF can source up to 2mA. Bypass
REF with a 10nF capacitor and a 4.7µF capacitor to
RGND. It is important to select a low ESR capacitor and
keep the trace resistance as low as possible.
DIGITAL OUTPUT CODE
111...111
111...110
000...000
000...001
INPUT VOLTAGE (LSB)
FS
FS - 3/2 LSB
FULL-SCALE
TRANSITION
111...101
000...011
000...010
FS =
V
REF
ZS = 0
1 LSB =
V
REF
4096
0
1
2
3
Figure 4a. MAX1377/MAX1379 Unipolar Transfer Function (U/B
= Low)
DIGITAL OUTPUT CODE
011...111
011...100
100...000
100...001
DIFFERENTIAL INPUT VOLTAGE (LSB)
+FS
V
REF
- 1 LSB
+FS - 3/2 LSB
FULL-SCALE
TRANSITION
000...000
111...111
111...110
+FS =
V
REF
2
ZS = 0
1 LSB =
V
REF
4096
-FS
000...010
000...001
111...101
-FS =
-V
REF
2
MAX1377/
MAX1379
MAX1383
+FS = 4V
REF
ZS = 0
-FS = -4V
REF
1 LSB =
8 x V
REF
4096
Figure 5. Bipolar Transfer Function (U/B = High)
T/H3pF
R2
R4
REF (2.5V)
R1
R3
INTERNAL
SIGNAL
GROUND
INPUT
R
IN
~ 11KΩ (typ)
INA
Figure 3b. MAX1383 Equivalent Input Circuit
DIGITAL OUTPUT CODE
111...111
111...110
000...000
000...001
INPUT VOLTAGE (LSB)
FULL-SCALE
TRANSITION
111...101
000...011
000...010
MAX1383
+FS = 4V
REF
-FS = -4V
REF
ZS = 0
1 LSB =
8 x V
REF
4096
+FS
V
REF
- 1 LSB
+FS - 3/2 LSB
-FS
Figure 4b. MAX1383 Single-Ended Input