MAX038CPP Maxim Integrated Products, MAX038CPP Datasheet - Page 10

• 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: -

When the MAX038’s frequency is controlled by a volt-
age source (V
output frequency is a direct function of V
the above equations. Varying V
tor frequency. For example, using a 10kΩ resistor for
R
large frequency deviations (up to 375:1). Select R
that I
width of the I
lating signal’s highest frequency, is typically 2MHz.
I
currents from several sources. This allows the output
frequency to be a function of the sum of several vari-
ables. As V
due to the offset voltage of I
Output frequency will be offset 1% from its final value
for 10 seconds after power-up.
FADJ Input The output frequency can be modulated by
FADJ, which is intended principally for fine frequency
control, usually inside phase-locked loops. Once the
funda-mental, or center frequency (F
may be changed further by setting FADJ to a voltage
other than 0V. This voltage can vary from -2.4V to
+2.4V, causing the output frequency to vary from 1.7 to
0.30 times the value when FADJ is 0V (F
Voltages beyond ±2.4V can cause instability or cause
the frequency change to reverse slope.
The voltage on FADJ required to cause the output to
deviate from Fo by Dx (expressed in %) is given by the
formula:
where V
and +2.4V.
Note: While I
tal, or center frequency (F
% deviation from F
corresponding to plus and minus deviation.
The voltage on FADJ for any frequency is given by the
formula:
where:
Likewise, for period calculations:
where:
High-Frequency Waveform Generator
10
IN
IN
can be used as a summing point to add or subtract
and sweeping V
______________________________________________________________________________________
V
V
F
F
V
t
t
IN
x
o
x
o
FADJ
FADJ
FADJ
= output period
= period when V
stays within the 2µA to 750µA range. The band-
= output frequency
= frequency when V
FADJ
= 3.43 x (t
= -0.0343 x D
= (F
IN
IN
IN
, the voltage on FADJ, is between -2.4V
IN
approaches 0V, the I
is directly proportional to the fundamen-
control amplifier, which limits the modu-
o
) in series with a fixed resistor (R
- F
o
x
. V
) ÷ (0.2915 x F
x
IN
- t
FADJ
FADJ
o
from 20mV to 7.5V produces
x
) ÷ t
o
), V
IN
FADJ
= 0V.
goes to either side of 0V,
.
x
FADJ
IN
= 0V.
modulates the oscilla-
o
is linearly related to
) [6]
IN
o
) is set by I
[5]
[7]
error increases
IN
as shown in
o
±70%).
IN
), the
IN
IN
, it
so
Conversely, if V
by:
and the period (tx) is:
FADJ has a 250µA constant current sink to V- that must
be furnished by the voltage source. The source is usu-
ally an op-amp output, and the temperature coefficient
of the current sink becomes unimportant. For manual
adjustment of the deviation, a variable resistor can be
used to set V
temperature coefficient becomes significant. Since
external resistors cannot match the internal tempera-
ture-coefficient curve, using external resistors to pro-
gram V
when the operator can correct for any errors. This
restriction does not apply when V
source.
A variable resistor, R
and FADJ provides a convenient means of manually
setting the frequency deviation. The resistance value
(R
V
algebraic convention. For example, if V
(+58.3% deviation), the formula becomes:
The FADJ circuit adds a small temperature coefficient
to the output frequency. For critical open-loop applica-
tions, it can be turned off by connecting FADJ to GND
(not REF) through a 12kΩ resistor (R1 in Figure 2). The -
250µA current sink at FADJ causes -3V to be devel-
oped across this resistor, producing two results. First,
the FADJ circuit remains in its linear region, but discon-
nects itself from the main oscillator, improving tempera-
ture stability. Second, the oscillator frequency doubles.
If FADJ is turned off in this manner, be sure to correct
equations 1-4 and 6-9 above, and 12 and 14 below by
doubling F
the normal output frequency, it does not double the
upper frequency limit. Do not operate FADJ open cir-
cuit or with voltages more negative than -3.5V. Doing
so may cause transistor saturation inside the IC, lead-
ing to unwanted changes in frequency and duty cycle.
REF
F
) is:
F
t
R
R
x
and V
x
F
F
= t
= F
FADJ
= (V
= (+2.5V - (-2.0V)) ÷ 250µA
= (4.5V) ÷ 250µA
= 18kΩ
o
o
o
÷ (1 - [0.2915 x V
FADJ
REF
or halving t
x (1 - [0.2915 x V
is intended only for manual operation,
FADJ
FADJ
- V
are signed numbers, so use correct
, but then the 250µA current sink’s
FADJ
F
, connected between REF (+2.5V)
is known, the frequency is given
o
) ÷ 250µA
. Although this method doubles
FADJ
FADJ
])
FADJ
Programming FADJ
])
Disabling FADJ
[8]
[9]
is a true voltage
[10]
FADJ
is -2.0V