MAX038EVKIT Maxim Integrated Products, MAX038EVKIT Datasheet - Page 3

• Manufacturer Part Number: MAX038EVKIT
• Description: Evaluation Kit: Max038
• Manufacturer: Maxim Integrated Products

The MAX038 output amplitude is fixed at 2V
MAX038 output is capable of driving a capacitive load
up to 90pF. The MAX442 amplifier buffers the MAX038
output to a 50Ω coaxial cable. The MAX442 is set at a
gain of 2V/V, so that the output amplitude remains 1V/V
after the 50Ω back termination. The EV kit’s OUT pad
provides access to the output of the MAX038 prior to
the MAX442 buffer stage. The MAX442 output connects
to the BNC connector through a 50Ω resistor to back
terminate a 50Ω coaxial cable. When a terminated 50Ω
cable is connected, this resistor forms a voltage divider
with the load impedance, which attenuates the signal
by one-half. The MAX442 is operated with a 2V/V
closed-loop gain to provide unity gain at the 50Ω
cable’s output.
The MAX442 is actually a 2-channel amplifier. A built-
in multiplexer allows either of two input signals to be
selected. TTL-level address pin A0 selects either IN0
or IN1. The MAX038 output is connected to MAX442
input IN0. IN1 is unused and connected to ground; it
may be used by cutting the JU7 trace, thus discon-
necting IN1 from ground. Likewise, the MAX442
address pin A0 can be disconnected from ground by
cutting the JU8 trace. Pull up A0 to +5V to select IN1.
See the MAX442 data sheet for additional operation
details.
The MAX038 includes a 2.5V bandgap reference capa-
ble of sourcing 4mA and sinking 100µA. Access to the
reference voltage is provided at the REF pad. The ref-
erence voltage is primarily used to provide stable cur-
rent to IIN and to bias DADJ and FADJ.
_______________________________________________________________________________________
Reference Voltage
Output Buffer
p-p
. The
MAX038 Evaluation Kit
The components supplied with the EV kit allow an out-
put frequency range of 325kHz to 10MHz. The frequen-
cy range is controlled primarily by the oscillator capaci-
tor (C1) and the input current, which is a function of the
reference voltage and potentiometer R3. The resulting
frequency range can be shifted up or down depending
on the value of C1. Refer to the Output Frequency vs.
Input Current graph which appears in the Typical
Operating Characteristics of the MAX038 data sheet.
The upper end of the range can be extended by reduc-
ing C1. The lower end of the range can be reduced by
increasing the value of C1. Take care when selecting
alternate capacitors if stable operation over tempera-
ture is desired. Ceramic capacitors with low tempera-
ture coefficients give the best results. Refer to the
Selecting Resistors and Capacitors section of the
MAX038 data sheet for further details.
Refer to the SYNC Output and Phase Detector sections
of the MAX038 data sheet for details of circuit synchro-
nization. Access to the Phase Detector Input (PDI) and
SYNC is provided at pads PDI and SYNC.
High-speed transient currents in DGND and DV+ can
cause a switching spike in the output waveform at the
zero-crossing point. A lowpass output filter, as shown in
Figure 3 of the MAX038 data sheet, may be used to
greatly reduce the spike. Complete LC filter assemblies
(S3LP series) are available from Coilcraft (phone:
708-639-6400). If the SYNC output is not required, dis-
abling the SYNC circuit will eliminate the switching
spike. Cut the trace between the DV+ and +5V pads to
disable the SYNC output.
and Phase-Detector Input
Extending the Output
Frequency Range
Sync Output
3