MAX1438 Datasheet, PDF (13/22 Pages) Maxim Integrated Products – Octal, 12-Bit, 65Msps, 1.8V ADC with Serial LVDS Outputs Serial LVDS Outputs

Octal, 12-Bit, 65Msps, 1.8V ADC
with Serial LVDS Outputs
AVDD
IN_P
IN_N
INTERNAL
COMMON-MODE
BIAS*
MAX1438
INTERNAL
BIAS*
S2a
S4a
C2a
S4c
S4b
S1
C2b
GND
INTERNAL
COMMON-MODE
BIAS*
*NOT EXTERNALLY ACCESSIBLE
Figure 1. Internal Input Circuit
S2b
INTERNAL
BIAS*
SWITCHES SHOWN IN TRACK MODE
INTERNALLY
GENERATED
COMMON-MODE
LEVEL*
S5a
C1a
S3a
OUT
OTA
OUT
C1b
S3b
S5b
INTERNALLY
GENERATED
COMMON-MODE
LEVEL*
then presented to the first-stage quantizers and isolate
the pipelines from the fast-changing inputs. Analog
inputs, IN_P to IN_N, are driven differentially. For differ-
ential inputs, balance the input impedance of IN_P and
IN_N for optimum performance.
Reference Configurations (REFIO,
REFADJ, REFP, and REFN)
The MAX1438 provides an internal 1.24V bandgap ref-
erence or can be driven with an external reference volt-
age. The full-scale analog differential input range is
±FSR. FSR (full-scale range) is given by the following
equation:
FSR = ^{(0.700 × VREFIO)}
1.24V
where V_REFIO is the voltage at REFIO, generated inter-
nally or externally. For a V_REFIO = 1.24V, the full-scale
input range is ±700mV (1.4V_P-P).
Internal Reference Mode
Connect REFADJ to GND to use the internal bandgap
reference directly. The internal bandgap reference gen-
erates V_REFIO to be 1.24V with a 120ppm/°C tempera-
ture coefficient in internal reference mode. Connect an
external ≥ 0.1µF bypass capacitor from REFIO to GND
for stability. REFIO sources up to 200µA and sinks up
to 200µA for external circuits, and REFIO has a
75mV/mA load regulation. REFIO has > 1MΩ to GND
when the MAX1438 is in power-down mode. The inter-
nal reference circuit requires 100ms (C_REFP to GND =
C_REFN to GND = 1µF) to power up and settle when
power is applied to the MAX1438 or when PD transi-
tions from high to low.
To compensate for gain errors or to decrease or
increase the ADC’s FSR, add an external resistor
between REFADJ and GND or REFADJ and REFIO.
This adjusts the internal reference value of the
MAX1438 by up to ±5% of its nominal value. See the
Full-Scale Range Adjustments Using the Internal
Reference section.
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