CDP1879 View Datasheet(PDF) - Intersil
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CDP1879 Datasheet PDF : 18 Pages
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CDP1879, CDP1879C-1
TABLE 3. TYPICAL OSCILLATOR CIRCUIT PARAMETERS FOR SUGGESTED OSCILLATOR CIRCUIT, SEE FIGURE 6
PARAMETER
4.197MHz
2.097MHz
1.049MHz
32768Hz (NOTE)
UNITS
RF
22
C0
39
C1
5
RS
-
CL
-
Crystal Impedance
73
22
22
22
MΩ
39
39
39
pF
5
5
5
pF
-
-
200
kΩ
-
-
91
pF
200
200
50K (max.)
Ω
NOTE: CDP1879C-1 only.
Design Considerations for Stable Crystal Oscillation
1. Stray capacitances should be minimized for best oscilla-
tor performance. Circuit board traces should be kept to a
maximum of 1 inch, and there should be no parallel
traces.
2. A signal line or power source line must not cross or go
near the oscillator circuit line.
3. It is advisable to put a 0.1µF capacitor between VDD and
VSS of the CDP1879.
CDP1879
XTAL PIN 23
PIN 22
XTAL
RF
RS
CL
PARALLEL
RESONANT
CRYSTAL
CO
CI
CDP1879
XTAL PIN 23
EXTERNAL
FREQUENCY
SOURCE
PIN 22
XTAL
FIGURE 5. CONNECTIONS FOR AN EXTERNAL FREQUENCY
SOURCE APPLIED TO REAL-TIME CLOCK
FIGURE 6. SUGGESTED OSCILLATOR CIRCUIT APPLIED TO
REAL-TIME CLOCK (SEE TABLE 3)
Standby (Timekeeping) Voltage Operation
When any one of the four specified crystals is used with the
on-board oscillator, the Real-Time Clock can operate at a
minimum of 4V VDD. However, at 32kHz the clock will run
(timekeeping only, no device READ/WRITE accesses) down
to 3V at -40oC to +85oC and 2.5V at 0o to +70oC.
To achieve this low voltage operation, an external 32kHz clock
source must be supplied at the XTAL input (see Figure 7). The
standby requirements for CHIP SELECT/DESELECT are
listed in Table 4, and Figure 8 indicates the timing waveforms.
Figure 9 illustrates the typical timekeeping curve over the full
temperature range.
22 MEG.
1
200K
RF
2
5PF
39PF
RL
3
+3V
14
24
23
22
4
1/3 CD54/74HC04
CDP1879
FIGURE 7. TYPICAL EXTERNAL CLOCK-SOURCE CIRCUIT
4-115
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