MAX038CPP Maxim Integrated Products, MAX038CPP Datasheet - Page 9

• Manufacturer Part Number: MAX038CPP
• Description: IC GEN WAVEFORM HI-FREQ 20-DIP
• Manufacturer: Maxim Integrated Products
• Type: Waveform Generatorr

Specifications of MAX038CPP

• Frequency: 20MHz
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 45mA
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 20-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Count: -

A stable 2.5V reference voltage, REF, allows simple
determination of IIN, FADJ, or DADJ with fixed resistors,
and permits adjustable operation when potentiometers
are connected from each of these inputs to REF. FADJ
and/or DADJ can be grounded, producing the nominal
frequency with a 50% duty cycle.
The output frequency is inversely proportional to
capacitor CF. CF values can be selected to produce
frequencies above 20MHz.
A sine-shaping circuit converts the oscillator triangle
wave into a low-distortion sine wave with constant
amplitude. The triangle, square, and sine waves are
input to a multiplexer. Two address lines, A0 and A1,
control which of the three waveforms is selected. The
output amplifier produces a constant 2VP-P amplitude
(±1V), regardless of wave shape or frequency.
The triangle wave is also sent to a comparator that pro-
duces a high-speed square-wave SYNC waveform that
can be used to synchronize other oscillators. The SYNC
circuit has separate power-supply leads and can be
disabled.
Two other phase-quadrature square waves are gener-
ated in the basic oscillator and sent to one side of an
"exclusive-OR" phase detector. The other side of the
phase-detector input (PDI) can be connected to an
external oscillator. The phase-detector output (PDO) is
a current source that can be connected directly to
FADJ to synchronize the MAX038 with the external
oscillator.
The MAX038 can produce either sine, square, or trian-
gle waveforms. The TTL/CMOS-logic address pins (A0
and A1) set the waveform, as shown below:
X = Don’t care.
Waveform switching can be done at any time, without
regard to the phase of the output. Switching occurs
within 0.3µs, but there may be a small transient in the
output waveform that lasts 0.5µs.
The output frequency is determined by the current
injected into the IIN pin, the COSC capacitance (to
ground), and the voltage on the FADJ pin. When
A0
X
0
1
A1
1
0
0
_______________________________________________________________________________________
High-Frequency Waveform Generator
Waveform Selection
Waveform Timing
Triangle wave
WAVEFORM
Square wave
Sine wave
Output Frequency
V
given by the formula:
The period (to) is:
where:
For example:
and
Optimum performance is achieved with IIN between
10µA and 400µA, although linearity is good with I
between 2µA and 750µA. Current levels outside of this
range are not recommended. For fixed-frequency oper-
ation, set IIN to approximately 100µA and select a suit-
able capacitor value. This current produces the lowest
temperature coefficient, and produces the lowest fre-
quency shift when varying the duty cycle.
The capacitance can range from 20pF to more than
100µF, but stray circuit capacitance must be minimized
by using short traces. Surround the COSC pin and the
trace leading to it with a ground plane to minimize cou-
pling of extraneous signals to this node. Oscillation
above 20MHz is possible, but waveform distortion
increases under these conditions. The low frequency
limit is set by the leakage of the COSC capacitor and
by the required accuracy of the output frequency.
Lowest frequency operation with good accuracy is usu-
ally achieved with 10µF or greater non-polarized
capacitors.
An internal closed-loop amplifier forces IIN to virtual
ground, with an input offset voltage less than ±2mV. IIN
may be driven with either a current source (IIN), or a
voltage (V
between REF and IIN provides a convenient method of
generating I
series with a resistor, the formula for the oscillator fre-
quency is:
and:
FADJ
Fo (MHz) = I
to (µs) = C
I
750µA)
C
(20pF to >100µF).
0.5MHz = 100µA ÷ 200pF
2µs = 200pF ÷ 100µA
Fo (MHz) = VIN ÷ [R
to (µs) = C
IN
F
= 0V, the fundamental output frequency (Fo) is
= current injected into IIN (between 2µA and
= capacitance connected to COSC and GND
IN
IN
) in series with a resistor (R
: I
F
F
IN
(pF) x R
(pF) ÷ I
IN
= V
(µA) ÷ C
REF
IN
IN
IN
/R
÷ V
(µA)
IN
x C
F
.) When using a voltage in
(pF)
IN
F
(pF)]
[1]
[2]
[3]
[4]
IN
). (A resistor
IN
9