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MAX038 Evaluation Kit
_______________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 50 coaxial cable. The MAX038 EV kit is fully assembled and tested.
___________________________Features
o 325kHz to 10MHz Operation o Adjustable Duty Cycle o 2.5V Reference Output o TTL-Compatible SYNC Output o Fully Assembled and Tested
Evaluates: MAX038
____________________Component List
DESIGNATION U1 U2 C1 C2, C3, C5, C7, C9, C10, C11, C12 C4, C6, C8 R1, R2 R3 R4, R5 R6 R7, R8 R9, R10, R11 R12 JU1, JU2, JU5 JU3, JU4 None J1 QTY 1 1 1 8 3 2 1 2 1 2 3 1 3 2 5 1 DESCRIPTION MAX038CPP MAX442CPA 82pF capacitor 0.1F capacitors 4.7F capacitors 20k potentiometers 50k potentiometer 10k, 5% resistors 51, 5% resistor 270, 5% resistors 0 resistors 3.3k, 5% resistor 2-pin headers 3-pin headers Shunts BNC jack
______________Ordering Information
PART MAX038EVKIT-DIP TEMP. RANGE 0C to +70C BOARD TYPE Through-Hole
______________________________EV Kit
_________________________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 50 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
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MAX038 Evaluation Kit Evaluates: MAX038
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.
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 50A to 725A. With the VADJ pin grounded, the fundamental output frequency (Fo) is as follows: Fo (MHz) = IIN(A) / COSC (pF) where: IIN = current injected into IIN = VREF / (R3 + R12) = 2.5V / (0k to 50k + 3.3k) COSC = 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 3.3k resistor in series with the device IIN pin. [1]
_______________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 10k pull-up resistors to +5V on the A0 and A1 address lines.
Table 1. Waveform Jumper Select
JU1 Don't Care Open Short JU2 Open Short Short OUTPUT WAVEFORM Sine Wave Triangle Wave Square Wave
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 (F o ), 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.
Table 2. Frequency and Duty-Cycle Jumper Select
JUMPER JU3 JU4 SHUNT LOCATION 1&2 2&3 1&2 2&3 MAX038 OUTPUT Adjustable Frequency Pre-Set Frequency* Adjustable Duty Cycle Fixed 50% Duty Cycle
* Note: Frequency pre-set by oscillator capacitor (C1) and input current (position of R3) as specified by formula [1].
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.
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.
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MAX038 Evaluation Kit
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 50 coaxial cable. The MAX442 is set at a gain of 2V/V, so that the output amplitude remains 1V/V after the 50 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 50 resistor to back terminate a 50 coaxial cable. When a terminated 50 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 50 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.
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.
Evaluates: MAX038
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.
Reference Voltage
The MAX038 includes a 2.5V bandgap reference capable of sourcing 4mA and sinking 100A. 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.
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MAX038 Evaluation Kit Evaluates: MAX038
1 8 JU8 CUT HERE V+ VOUT 5 IN7 +5V 6 R7 270 R6 51 J1 BNC OUTPUT C12 0.1F
IN0
U2
A0
2 JU7 CUT HERE 3 4 C11 0.1F
GND IN1 V-
MAX442
-5V
R8 270
REF +5V R4 10k JU1 R5 10k C2 0.1F 1 REF V20 R9 0 OUT C4 4.7F C5 0.1F -5V
2
GND
OUT
19
JU2 A0
3
GND A0
18
U1
A1
4 C1 82pF 5
A1
MAX038
V+
17 C8 4.7F CUT HERE TO DISABLE SYNC
+5V C9 0.1F
COSC
DV+
16 C6 4.7F C7 0.1F
DV+
6 R10 0 DADJ R1 20k 1 2 JU4 C10 0.1F R2 20k R11 0 1 2 JU3 R3 50k 10 JU5 R12 3.3k 3 3 8
GND
DGND
15
GND
JU6 CUT HERE 7 DADJ SYNC 14 SYNC
FADJ
PDI
13
PDI
9
GND
PDO
12 PDO C3 0.1F
IIN
GND
11
FADJ IIN
Figure 1. MAX038 EV Kit Schematic
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MAX038 Evaluation Kit Evaluates: MAX038
Figure 2. MAX038 EV Kit Component Placement Guide--Component Side
_______________________________________________________________________________________
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MAX038 Evaluation Kit Evaluates: MAX038
Figure 3. MAX038 EV Kit PC Board Layout--Component Side
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MAX038 Evaluation Kit Evaluates: MAX038
Figure 4. MAX038 EV Kit PC Board Layout--Solder Side
_______________________________________________________________________________________
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MAX038 Evaluation Kit Evaluates: MAX038
NOTES
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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