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CDP6872E Schematic ( PDF Datasheet ) - Intersil Corporation

Teilenummer CDP6872E
Beschreibung Low Power Crystal Oscillator
Hersteller Intersil Corporation
Logo Intersil Corporation Logo 




Gesamt 15 Seiten
CDP6872E Datasheet, Funktion
CDP6872
January 1996
Low Power Crystal Oscillator
Features
Description
• Single Supply Operation at 32kHz . . . . . . . 2.0V to 7.0V
• Operating Frequency Range. . . . . . . . 10kHz to 10MHz
• Supply Current at 32kHz . . . . . . . . . . . . . . . . . . . . . .5µA
• Supply Current at 1MHz . . . . . . . . . . . . . . . . . . . .130µA
• Drives 2 CMOS Loads
• Only Requires an External Crystal for Operation
Applications
• Battery Powered Circuits
• Remote Metering
• Embedded Microprocessors
• Palm Top/Notebook PC
The CDP6872 is a very low power crystal-controlled oscillators
that can be externally programmed to operate between 10kHz
and 10MHz. For normal operation it requires only the addition
of a crystal. The part exhibits very high stability over a wide
operating voltage and temperature range.
The CDP6872 also features a disable mode that switches
the output to a high impedance state. This feature is useful
for minimizing power dissipation during standby and when
multiple oscillator circuits are employed.
Ordering Information
PART
NUMBER
CDP6872E
CDP6872M
TEMPERATURE
RANGE
-40oC to +85oC
-40oC to +85oC
PACKAGE
8 Lead Plastic DIP
8 Lead Plastic SOIC (N)
CDP6872H
-40oC to +85oC DIE
Pinout
CDP6872 (PDIP, SOIC)
TOP VIEW
VDD 1
OSC IN 2
OSC OUT 3
VSS 4
8 ENABLE
7 FREQ 2
6 FREQ 1
5 OUTPUT
Typical Application Circuit
VDD
0.1µf
32.768kHz
CRYSTAL
18
27
CDP6872
36
45
32.768kHz
CLOCK
32.768kHz MICROPOWER CLOCK OSCILLATOR
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
http://www.intersil.com or 407-727-9207 | Copyright © Intersil Corporation 1999
1
File Number 4069






CDP6872E Datasheet, Funktion
CDP6872
Typical values of the capacitors in Figure 2 are shown below.
Some trial and error may be required before the best combi-
nation is determined. The values listed are total capacitance
including parasitic or other sources. Remember that in the
10kHz to 100kHz frequency range setting the CDP6872
switches in two internal 15pF capacitors.
CRYSTAL
FREQUENCY
32kHz
1MHz
2MHz
LOAD CAPS
C1, C2
33pF
33pF
25pF
TRIMMER CAP
C3
5-50pF
5-50pF
5-50pF
Layout Considerations
Due to the extremely low current (and therefore high imped-
ance) the circuit board layout of the CDP6872 must be given
special attention. Stray capacitance should be minimized.
Keep the oscillator traces on a single layer of the PCB. Avoid
putting a ground plane above or below this layer. The traces
between the crystal, the capacitors, and the OSC pins
should be as short as possible. Completely surround the
oscillator components with a thick trace of VDD to minimize
coupling with any digital signals. The final assembly must be
free from contaminants such as solder flux, moisture, or any
other potential source of leakage. A good solder mask will
help keep the traces free of moisture and contamination over
time.
4MHz
22pF
5-100pF
Further Reading
Crystal Pullability
Figure 4 shows the basic equivalent circuit for a crystal and
its loading circuit.
C1
CM LM RM
VDD
C2
2
OSC IN
C0
3
OSC OUT
FIGURE 4.
Where:
CM = Motional Capacitance
LM = Motional Inductance
RM = Motional Resistance
C0 = Shunt Capacitance
CCL = ----C-----1-----1-------1+-----C-----1----2------- = Equivalent Crystal Load
Al Little “HA7210 Low Power Oscillator: Micropower Clock
Oscillator and Op Amps Provide System Shutdown for
Battery Circuits”. Intersil Application Note AN9317.
Robert Rood “Improving Start-Up Time at 32KHz for the
HA7210 Low Power Crystal Oscillator”. Intersil Application
Note AN9334.
S. S. Eaton “Timekeeping Advances Through COS/MOS
Technology”. Intersil Application Note ICAN-6086.
E. A. Vittoz et. al. “High-Performance Crystal Oscillator cir-
cuits: Theory and Application”. IEEE Journal of Solid-State
Circuits, Vol. 23, No3, June 1988, pp774-783.
M. A. Unkrich et. al. “Conditions for Start-Up in Crystal Oscil-
lators”. IEEE Journal of Solid-State Circuits, Vol. 17, No1,
Feb. 1982, pp87-90.
Marvin E. Frerking “Crystal Oscillator Design and Tempera-
ture Compensation”. New York: Van Nostrand-Reinhold,
1978. Pierce Oscillators Discussed pp56-75.
If loading capacitance is connected to a Series Mode Crys-
tal, the new Parallel Mode frequency of resonance may be
calculated with the following equation:
FP = FS 1 + 2--------C----0--C---+--M---C-----C----L-----
Where: FP = Parallel Mode Resonant Frequency
FS = Series Mode Resonant Frequency
In a similar way, the Series Mode resonant frequency may
be calculated from a Parallel Mode crystal and then you may
calculate how much the frequency will “pull” with a new load.
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CDP6872E pdf, datenblatt
CDP6872
Typical Performance Curves (Continued)
30
25
20
15
10
5
0
-5
-10
-15
-20
2
32kHz
1MHz
5MHz
10MHz
DEVIATION FROM 5.0V FREQUENCY
46
VDD SUPPLY VOLTAGE (V)
FIGURE 29. FREQUENCY CHANGE vs VDD
FIN = 5MHz, F1 = 0, F2 = 0, CL = 30pF, VCC = 5V
13
12 Tf GENERATOR(1VP-P)
11
10
9
8 Tr GENERATOR(1VP-P)
7 Tf XTAL AT +25oC
6
5
4 Tr XTAL AT +25oC
3
2
-100
-50
0
50 100 150
TEMPERATURE (oC)
FIGURE 31. RISE/FALL TIME vs TEMPERATURE
VCC = 5V, GENERATOR(1VP-P)
30
Tf (FIN = 100kHz)
25
Tf (FIN = 5MHz)
Tr
20 (FIN = 5MHz)
Tr (FIN = 100kHz)
15
10
5
10 20 30 40 50 60 70 80 90 100 110
CL (pF)
FIGURE 33. RISE/FALL TIME vs CL
VCC = 5V, CL = 30pF, GENERATOR(1VP-P)
6
5
4 FIN = 5MHz, F1 = 0, F2 = 0
3
2
1
FIN = 100kHz, F1 = 1, F2 = 1
0
-100
-50 0
50 100
TEMPERATURE (oC)
FIGURE 30. EDGE JITTER vs TEMPERATURE
150
FIN = 100kHz, F1 = 1, F2 = 1, CL = 30pF, VCC = 5V
12
11 Tf GENERATOR(1VP-P)
10
9
8 Tr GENERATOR(1VP-P)
7
Tf XTAL AT +25oC
6
5 Tr XTAL AT +25oC
4
3
2
-100
-50
0
50 100
TEMPERATURE (oC)
FIGURE 32. RISE/FALL TIME vs TEMPERATURE
150
CL = 18pF, GENERATOR(1VP-P)
15
14 Tf (FIN = 5MHz)
13
Tf (FIN = 100kHz)
12
11 Tr (FIN = 5MHz)
10 Tr (FIN = 100kHz)
9
8
7
6
5
4
23456
VCC (+VOLTS)
7
FIGURE 34. RISE/FALL TIME vs VCC
8
9
Refer to Test Circuit (Figure 1).
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