Datasheet

Table 1. Power Options for the Santa Fe Subsystem Reference Design
Power Type Jumper Shunt Input Voltage (V) Input Current (mA, typ)
On-board isolated power
JU3: 1-2
JU4: 2-3
JU5: 1-2
3.3 221
External power
JU3: 2-3
JU4: 1-2
JU5: 2-3
3.3 6.3
+12 30.4
-12 7.3
Table 2. Supported Platforms and Ports
Supported Platforms Ports
Nexys
™
3 platform (Spartan
®
-6)
JB1
ZedBoard
™
platform (Zynq
®
-7020)
JA1
The Santa Fe hardware design is specifically optimized for applications that use -10V to +10V, 0 to 10V, and 4–
20mA signals. Depending on the application requirements, certain portions of the circuit may be omitted. A
complete discussion of what portions are needed or may be omitted follows. See the file for the schematic under
the All Design Files section.
The MAX1301 (U3) is a 16-bit, successive-approximation register (SAR) ADC with unique multirange inputs
capable of accepting input voltage signals up to +12.288V to -12.288V. The ADC also has integrated analog
input buffers with a 17k½ input resistance.
The first MAX9632 amplifier (U1) is optimized for low-noise, -10V to +10V input voltages. The second MAX9632
amplifier (U2) is optimized for low-noise, 4–20mA input currents. Both U1 and U2 provide high input impedance
for input signals that have a large source resistance, or in the case of the 4–20mA loop, a 250½ load resistance.
Large source resistances often attenuate signals by an undesirable factor. Add an optional 500½ series resistor
in front of both MAX9632 amplifiers if input protection is desired while the Santa Fe design is not powered. The
500½ series resistor prevents the input current from exceeding the maximum input current specification when
10V is applied at the input and the Santa Fe board has no power.
If the signal source has a significantly low source resistance compared to 17k½, or in the case of the 4–20mA
loop, if the parallel combination of 250½ and 17k½ provides acceptable accuracy in the application, then U1 and
U2 can be eliminated. ADC channels AIN1 and AIN3 are examples of using only the internal 17k½ analog input
buffers.
Although the MAX1301 ADC has an internal 4.096V voltage reference, for highest accuracy use the external
MAX6126 (U4) voltage reference with 0.02% initial accuracy and a 3ppm/°C maximum temperature coefficient
(tempco).
The MAX256 (U5) provides an isolated, functional insulation class power solution that accepts 3.3V and converts
it to ±12V using an off-the-shelf TGM-H281NF Halo
®
transformer with a 1:2.6 primary to secondary turns ratio
plus an external on-board voltage-doubler circuit. Post-regulation is accomplished using the MAX1659 low
dropout (LDO) regulators. The ±12V isolated power solution is optional and is only needed for applications that
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