Datasheet
Table 1. Power Options for the Fresno Subsystem Reference Design
Power Type Jumper Shunt Input Voltage (V) Input Current (mA, typ)
On-board isolated power
JU1: 1–2
JU2: 2–3
JU3: 1–2
3.3 71
External power
JU1: 2–3
JU2: 1–2
JU3: 2–3
6 10
-5 2
Table 2. Supported Platforms and Ports
Supported Platforms Port
Nexys
™
3 platform (Spartan
®
-6)
JB1
ZedBoard
™
platform (Zynq
®
-7020)
JA1
The Fresno hardware design provides isolated power (MAX256) and isolated data (MAX14850) for a high-
accuracy, 0 to 10V signal, analog-to-digital conversion application.
The MAX44250 (U1) op amp input circuit attenuates and buffers a 0 to10V signal to match the input range of
the ADC (MAX11100), which is 0 to 4.096V.
The MAX11100 (U2) is a 16-bit, successive-approximation register (SAR) ADC with AutoShutdown
™
and fast
1.1µs wake-up features. The ADC's reference input is driven by an ultra-high-precision 4.096V voltage
reference, the MAX6126 (U3), with 0.02% initial accuracy and a 3ppm/°C maximum temperature coefficient
(tempco).
The MAX256 (U4) provides an isolated, functional insulation class power solution that accepts 3.3V and
converts it to ±6V using an off-the-shelf TGN-H251NF Halo
®
transformer with a 1:1 primary to secondary turns
ratio plus an external on-board voltage-doubler circuit. Post-regulation is accomplished using the MAX1659 low
dropout (LDO) regulator (for +5V) and the MAX1735 low dropout (LDO) regulator (for -3V). Data isolation is
accomplished using the MAX14850 (U5) digital data isolator. The combined power and data isolation achieved
is 600V
RMS
.
The signal input impedance of the Fresno subsystem is 5kΩ (R19 + R20). Ideally, the input impedance should
be high, but larger resistors induce higher thermal noise and degrade the noise performance. Therefore, the
values of the input resistors R19 and R20 are application dependent. Note that when choosing different values
for the input resistors to properly attenuate a 10V signal to a 4V signal, R19 = 1.5 × R20.
To use the on-board isolated power supplies, move the shunts on jumper JU1 and JU3 to the 1–2 position and
move the shunt on jumper JU2 to the 2–3 position. To use an external power supply, move the shunts on
jumper JU1 and JU3 to the 2–3 position and move the shunt on jumper JU2 to the 1–2 position. Connect the
ground terminal of the external power supply to the GND2 connector, the +6V to +12V supply to the EXT_V+
connector, and the -3.3V to -5V supply to the EXT_V- connector. See Table 1 for the jumper settings and the
input current requirements.
Detailed Description of Firmware for Nexys 3 Platform
The Fresno firmware design was initially released for the Nexys 3 development kit and targeted a Microblaze
™
Page 3 of 11