MAXIM MAX038 Technical data

Evaluates: MAX038

MAX038 Evaluation Kit

________________________________________________________________ Maxim Integrated Products

1

_______________General Description

The MAX038 evaluation kit (EV kit) is a high-frequency
function generator capable of producing accurate tri­angle/sawtooth, sine, and square/pulse waveforms up
to 10MHz, using the supplied components. Output fre­quency and duty cycle are easily adjusted with on­board potentiometers. Removable jumpers select sine,
square, or triangle waveforms, or fix the duty cycle at
50%. The output is buffered with a MAX442 amplifier
capable of driving a 50Ω coaxial cable. The MAX038
EV kit is fully assembled and tested.

___________________________Features

♦ 325kHz to 10MHz Operation
♦ Adjustable Duty Cycle
♦ 2.5V Reference Output
♦ TTL-Compatible SYNC Output
♦ Fully Assembled and Tested

____________________Component List

_________________________Quick Start

The MAX038 EV kit is a fully assembled and tested
board. Follow these steps to verify board operation. Do

not turn on the power supply until all connections
are completed.

1) Connect a +5V supply to the pad marked +5V.
Connect a -5V supply to the pad marked -5V.
Connect ground(s) to the GND pad.

2) Connect an oscilloscope to the BNC jack marked
OUTPUT through a terminated 50Ω cable. The
MAX038 output prior to the amplifier stage may also
be monitored using an oscilloscope probe at the
OUT pad.

3) Place the shunt across pins 2 and 3 of JU4 for 50%
duty cycle. Place the shunt across pins 1 and 2 of

______________Ordering Information

______________________________EV Kit

DESIGNATION QTY DESCRIPTION

U1 1 MAX038CPP
U2 1 MAX442CPA
C1 1 82pF capacitor

C2, C3, C5, C7,

C9, C10, C11,

C12

8 0.1µF capacitors

C4, C6, C8 3 4.7µF capacitors

R1, R2 2 20kΩ potentiometers

R3 1 50kΩ potentiometer

R4, R5 2 10kΩ, 5% resistors

R6 1 51Ω, 5% resistor

R7, R8 2 270Ω, 5% resistors

R9, R10, R11 3 0Ω resistors

R12 1 3.3kΩ, 5% resistor

JU1, JU2, JU5 3 2-pin headers

JU3, JU4 2 3-pin headers

None 5 Shunts

J1 1 BNC jack

PART

MAX038EVKIT-DIP 0°C to +70°C

TEMP. RANGE BOARD TYPE

Through-Hole

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

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JU3 to allow the frequency to be adjusted. Verify
that there is a shunt on JU5.

4) Verify the shunts on JU1 and JU2 for a square-wave
output. Refer to Table 1 for alternate waveform
selections.

5) Apply power and verify the output waveform.

_______________Detailed Description

Waveform Selection

To select the desired output waveform, place shunts
across JU1 and JU2 in the combinations shown in
Table 1. These jumpers set address pins A0 and A1 to
TTL/CMOS-logic levels. External control may be initiat­ed by connecting an external source to the A0 and
A1 pads and removing the shunts on JU1 and JU2.
Note that there are 10kΩ pull-up resistors to +5V on the
A0 and A1 address lines.

* Note: Frequency pre-set by oscillator capacitor (C1) and input

current (position of R3) as specified by formula [1].

Output Frequency

The output frequency is controlled by the oscillator
capacitor (C1), the current injected into the IIN pin, and
the voltage on the FADJ pin. The EV kit allows indepen­dent adjustment of both input current (R3) and FADJ
voltage (R2). Refer to the

Detailed Description

section
of the MAX038 data sheet for additional theory of oper­ation.

Input Current Control

The current injected into the IIN pin acts as the primary
frequency-adjustment control. The R3 potentiometer
varies the current to the MAX038’s IIN pin. The input
current can be easily monitored by removing the JU5
shunt and placing a current meter across the JU5 pins.
The components supplied on the EV kit will allow an
input current range of 50µA to 725µA. With the VADJ
pin grounded, the fundamental output frequency (Fo) is
as follows:

Fo(MHz) = IIN(µA) ÷ C

OSC

(pF) [1]

where: IIN= current injected into IIN

= V

REF

÷ (R3 + R12)

= 2.5V ÷ (0kΩ to 50kΩ + 3.3kΩ)

C

OSC

= external oscillator capacitor (C1)

To use an external input current, connect the external
current source to the IIN pad and remove the JU5 shunt
completely. Note that there is a 3.3kΩ resistor in series
with the device IIN pin.

FADJ Control

Varying the FADJ voltage will also vary the output fre­quency. With a shunt across pins 1 and 2 of JU3, the
R2 potentiometer will vary the voltage applied to the
FADJ pin. With the JU3 shunt on pins 2 and 3, the FADJ
pin is grounded. Grounding the FADJ pin sets the out­put to the fundamental output frequency (Fo), as
given by equation [1].

To use an external FADJ voltage, connect the external
source to the FADJ pad and remove the JU3 shunt
completely. Limit the external FADJ voltage to ±2.4V.

Duty-Cycle Control

The voltage on the DADJ pin controls the duty cycle of
the output waveform. With the JU4 shunt on pins 1 and 2,
the R1 potentiometer will vary the voltage applied to the
DADJ pin, thus varying the duty cycle 15% to 85%. With
the JU4 shunt on pins 2 and 3, the DADJ pin is grounded.
Grounding the DADJ pin fixes the duty cycle at 50%.

To use an external DADJ voltage, connect the external
voltage source to the DADJ pad and remove the JU4
shunt completely. Limit the external DADJ voltage to
±2.3V.

Evaluates: MAX038

MAX038 Evaluation Kit

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Table 1. Waveform Jumper Select

Table 2. Frequency and Duty-Cycle Jumper Select

Fixed 50% Duty Cycle2 & 3

JU4

Adjustable Duty Cycle1 & 2

Pre-Set Frequency*2 & 3

JU3

Adjustable Frequency1 & 2

MAX038 OUTPUT

SHUNT

LOCATION

JUMPER

Square WaveShortShort

Triangle WaveShortOpen

Sine WaveOpenDon't Care

OUTPUT WAVEFORMJU2JU1

Output Buffer

The MAX038 output amplitude is fixed at 2V

p-p

. The
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 built­in 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 discon­necting 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.

Reference Voltage

The MAX038 includes a 2.5V bandgap reference capa­ble of sourcing 4mA and sinking 100µA. Access to the
reference voltage is provided at the REF pad. The ref­erence voltage is primarily used to provide stable cur­rent to IIN and to bias DADJ and FADJ.

Extending the Output

Frequency Range

The components supplied with the EV kit allow an out­put frequency range of 325kHz to 10MHz. The frequen­cy range is controlled primarily by the oscillator capaci­tor (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 reduc­ing 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 tempera­ture is desired. Ceramic capacitors with low tempera­ture coefficients give the best results. Refer to the

Selecting Resistors and Capacitors

section of the

MAX038 data sheet for further details.

Sync Output

and Phase-Detector Input

Refer to the

SYNC Output

and

Phase Detector

sections
of the MAX038 data sheet for details of circuit synchro­nization. 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, dis­abling the SYNC circuit will eliminate the switching
spike. Cut the trace between the DV+ and +5V pads to
disable the SYNC output.

Evaluates: MAX038

MAX038 Evaluation Kit

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