Rainbow Electronics MAX1208 - Manual (Page 15)

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 MAX1208 full-scale analog input range is
adjustable from ±0.35V to ±1.15V with a common-
mode input range of V
DD / 2 ±0.5V. The MAX1208 pro-
vides three modes of reference operation. The voltage
at REFIN (V
REFIN ) sets the reference operation mode
(Table 1).
To operate the MAX1208 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 / 4 ,
V
REFN
= V
DD
/ 2
- V REFIN / 4. The REFIN input impedance is very large
(>50M Ω). When driving REFIN through a resistive
divider, use resistances
≥10kΩ to avoid loading
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
MAX1208 REFOUT. In buffered external reference
mode, apply a stable 0.7V to 2.3V 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 /
4, and V REFN = V DD / 2 - V REFIN / 4.
To operate the MAX1208 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 ).
MAX1208
12-Bit, 80Msps, 3.3V ADC
______________________________________________________________________________________ 15
t
AD
T/H
CLKN
CLKP
t AJ
TRACK HOLD TRACK HOLD TRACK HOLD TRACK HOLD
ANALOG
INPUT
SAMPLED
DATA
Figure 4. T/H Aperture Timing
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
/ 4
V REFN = V DD / 2 - V REFIN / 4
0.7V to 2.3V
Buffered External Reference Mode. Apply an external 0.7V to 2.3V 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 / 4
V REFN = V DD / 2 - V REFIN / 4
<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 ).
Table 1. Reference Modes