MAX12553 Datasheet, PDF (15/28 Pages) Maxim Integrated Products – 14-Bit, 65Msps, 3.3V ADC

14-Bit, 65Msps, 3.3V ADC
CLKP
CLKN
t_AD
ANALOG
INPUT
t_AJ
SAMPLED
DATA
T/H
TRACK
HOLD
TRACK
HOLD
TRACK
HOLD
TRACK
HOLD
Figure 4. T/H Aperture Timing
REFOUT sources up to 1.0mA and sinks up to 0.1mA
for external circuits with a load regulation of 35mV/mA.
Short-circuit protection limits I_REFOUT to a 2.1mA
source current when shorted to GND and a 0.24mA
sink current when shorted to V_DD.
Analog Inputs and Reference
Configurations
The MAX12553 full-scale analog input range is
adjustable from ±0.35V to ±1.10V with a common-
mode input range of V_DD/2 ±0.5V. The MAX12553 pro-
vides three modes of reference operation. The voltage
at REFIN (V_REFIN) sets the reference operation mode
(Table 1).
To operate the MAX12553 with the internal reference,
connect REFOUT to REFIN either with a direct short or
through a resistive divider. In this mode, COM, REFP,
and REFN are low-impedance outputs with V_COM =
V_DD/2, V_REFP = V_DD/2 + V_REFIN x 3/8, and V_REFN =
V_DD/2 - V_REFIN x 3/8. The REFIN input impedance is
very large (>50MΩ). When driving REFIN through a
resistive divider, use resistances ≥10kΩ to avoid load-
ing REFOUT.
Buffered external reference mode is virtually identical to
internal reference mode except that the reference
source is derived from an external reference and not
the MAX12553 REFOUT. In buffered external reference
mode, apply a stable 0.7V to 2.2V source at REFIN. In
this mode, COM, REFP, and REFN are low-impedance
outputs with V_COM = V_DD/2, V_REFP = V_DD/2 + V_REFIN x
3/8, and V_REFN = V_DD/2 - V_REFIN x 3/8.
To operate the MAX12553 in unbuffered external refer-
ence mode, connect REFIN to GND. Connecting REFIN
to GND deactivates the on-chip reference buffers for
COM, REFP, and REFN. With the respective buffers
deactivated, COM, REFP, and REFN become high-
impedance inputs and must be driven through sepa-
rate, external reference sources. Drive V_COM to V_DD/2
±5%, and drive REFP and REFN such that V_COM =
(V_REFP + V_REFN)/2. The full-scale analog input range is
±(V_REFP - V_REFN) x 2/3.
Table 1. Reference Modes
V_REFIN
REFERENCE MODE
35% V_REFOUT to 100%
V_REFOUT
Internal Reference Mode. Drive REFIN with REFOUT either through a direct short or a resistive divider.
The full-scale analog input range is ±V_REFIN/2:
V_COM = V_DD/2
V_REFP = V_DD/2 + V_REFIN x 3/8
V_REFN = V_DD/2 - V_REFIN x 3/8
0.7V to 2.2V
Buffered External Reference Mode. Apply an external 0.7V to 2.2V reference voltage to REFIN.
The full-scale analog input range is ±V_REFIN/2:
V_COM = V_DD/2
V_REFP = V_DD/2 + V_REFIN x 3/8
V_REFN = V_DD/2 - V_REFIN x 3/8
<0.4V
Unbuffered External Reference Mode. Drive REFP, REFN, and COM with external reference sources.
The full-scale analog input range is ±(V_REFP - V_REFN) x 2/3.
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