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 initiat-

ed by connecting an external source to the A0 and

A1 pads and removing the shunts on JU1 and JU2.

Note that there are 10k

Ω 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 indepen-

dent 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 oper-

ation.

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

as follows:

[1]

÷ (R3 + R12)

= 2.5V

÷ (0kΩ to 50kΩ + 3.3kΩ)

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

Ω resistor in series

with the device IIN pin.

FADJ Control

Varying the FADJ voltage will also vary the output fre-

quency. 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 out-

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.

MAX038 Evaluation Kit

2

_______________________________________________________________________________________

Table 1. Waveform Jumper Select

Table 2. Frequency and Duty-Cycle Jumper Select

Fixed 50% Duty Cycle

2 & 3

JU4

Adjustable Duty Cycle

1 & 2

Pre-Set Frequency*

2 & 3

JU3

Adjustable Frequency

1 & 2

MAX038 OUTPUT

SHUNT

LOCATION

JUMPER

Square Wave

Short

Short

Triangle Wave

Short

Open

Sine Wave

Open

Don't Care

OUTPUT WAVEFORM

JU2

JU1