supplies applied to analog and digital power planes.
However, the digital supply can be operated down to
+1.7V without compromising the board’s performance.
The logic analyzer’s threshold should be adjusted
accordingly.
Access to the output is provided through connector J1.
The 40-pin connector can easily interface directly to a
user-provided logic analyzer or data-acquisition system.
Power Supplies
The MAX1448 EV kit requires separate analog and digi-
tal power supplies for best performance. A +3V power
supply is used to power the analog portion of the
MAX1449/MAX1448/MAX1446/MAX1444 ADC and
the clock signal circuit. The MAX1449/MAX1448/
MAX1446/MAX1444 analog supply voltage has a range
of +2.7V to +3.3V; however, +3V must be supplied to
the EV kit (VAIN1, VAIN2) to meet the minimum input
voltage supply to the clock signal generator. A separate
+3.0V power supply is used to power the digital portion
(VDIN1, VDIN2) of the MAX1448 ADC and the buffer/dri-
ver, but it will operate with a voltage supply as low as
+1.7V and as high as +3.3V. Enhanced dynamic perfor-
mance can be achieved when the digital supply voltage
is lower than the analog supply voltage.
Clock
An on-board clock-shaping circuit generates a clock sig-
nal from an AC sine-wave signal applied to the CLOCK
SMA connector. The signal should not exceed 2.6V
P-P
.
The typical clock frequency should be 80MHz or less.
The frequency of the sinusoidal input signal determines
the sampling frequency of the ADC. A DS90LV028A dif-
ferential line receiver processes the input signal to pro-
duce the CMOS clock signal. The signal’s duty cycle can
be adjusted with potentiometer R34. A clock signal with a
50% duty cycle can be achieved by adjusting R34 until
+1.2V is produced across test points TP4 and TP5 at +3V
analog voltage supply (40% of the analog power supply).
Input Signal
The MAX1448 ADC is able to process differential or sin-
gle-ended analog input signals. The EV kit requires only
one single-ended analog input signal provided by the
user. During single-ended signal operation, the signal is
applied directly to the ADC, and in differential signal
operation, an on-board transformer takes the single-
ended analog signal and generates a differential analog
signal at the ADC’s differential input pins. For single-
ended or differential signal board operation, see Table 1
for jumper configuration.
Note: When a differential signal is applied to the ADC,
its positive and negative input pins each receive half of
the input signal supplied at SMA connector DIFF cen-
tered at (VAIN1) / 2.
MAX1448 Enable/Shutdown
The MAX1448 EV kit features jumpers to enable and dis-
able the MAX1448 (JU1) or its digital outputs (JU2). See
Table 1 for jumper settings.
External Voltage Reference
The MAX1448 ADC requires an input voltage reference
at pin 31 (REFIN) to set the full-scale analog signal volt-
age input. The ADC also has a stable on-chip voltage
reference of +2.048V that can be accessed at REFOUT.
The EV kit was designed to use the on-chip voltage ref-
erence by connecting REFIN to REFOUT through resis-
tor R40. The user can externally adjust the reference
level, and hence the full-scale range, by installing a
resistor at R39. The adjusted reference level can be cal-
culated by applying the following equation;
V
REFIN
= (R39 / (R40 + R39)) x V
REFOUT
where R39 is the value of the resistor installed, R40 is a
10kΩ resistor, and V
REFOUT
is +2.048V. Alternatively,
the user can also apply a stable, low-noise, external ref-
erence voltage directly at the REFIN pad to set the full
scale.
Evaluates: MAX1444/MAX1446/MAX1448/MAX1449
MAX1448 Evaluation Kit
_______________________________________________________________________________________ 3
Table 1. MAX1448 EV Kit Jumper Selection
