Rev. A
TECHNICAL NOTE 29
Using IQD Statek’s CX-1V Crystals (200-240kHz)
with Microchip Technology’s PIC16C73A Microcontroller
Overview
We recommend component values when
using IQD Statek’s CX-1V crystals in the
200-240 kHz range with Microchip Technolo-
gy’s PIC16C73A microcontroller (in the
XT mode). The large capacitors (47-68pF)
recommended in Table 14-2 of Microchip
Technology’s data sheet DS30390E cause
the PIC16C73A to overdrive Statek’s
crystals.
Recommended externally added
component values
As shown in Figure 1 (cf. Figure 14-3 in
Microchip Technology’s data sheet), the
oscillator portion of the PIC16C73A can
require up to three components in addition
to the crystal.
Figure 1
However, Statek recommends the addition
of only two with the values listed in Table 1.
Table 1
Component Recommended Component Value
RS
470 kΩ (±10%)
C2
10 pF (±10%)
C1
Addition not recommended
Circuit board layout considerations
Stray capacitance in the oscillator portion of
the board’s layout can influence the
oscillator’s performance. For instance, the
stray capacitances from the crystal pads to
ground add to the capacitances provided by
C1 and C2. Further, minimize the stray
capacitance between OSC1 and OSC2 and
the stray capacitance between the crystal
mounting pads on the board as these can
raise the gain requirement to the point that
the system will not oscillate.
Operating conditions
Other than the recommendations above, we
refer the reader to Microchip Technology’s
data sheet DS30390E for proper operating
conditions.
Typical operation
The typical motional resistance of a CX-1V
crystal in the 200-240 kHz frequency range
is 3 kΩ. With a supply voltage of 4-6 volts,
the circuit should start to oscillate within
0.5 seconds. The drive level (crystal
current) is approximately 12 µA (RMS) and
the circuit’s effective load capacitance is
approximately 4.5 pF.
Further information
Microchip Technology’s
Data Sheet DS30390E
PIC16C7X 8-bit CMOS
Microcontrollers with
A/D Converter
IQD Statek’s
Technical Note 25
Load Capacitance of a
Quartz Crystal and How
it Relates to the Effective
Load Capacitance (CL)
of a Pierce Oscillator
IQD Statek’s
Technical Note 31
Practical Analysis of the
Pierce Oscillator
IQD Statek Data Sheet Typical and maximum
crystal parameters, drive
level, etc.
OSC1 OSC2
PIC16C73A
XTAL
C1 C2
RS
IQD Frequency Products Ltd
Station Road
Crewkerne
Somerset
TA18 8AR
United Kingdom
Tel: +44 (0)1460 270200
Fax: +44 (0)1460 72578
Email: info@iqdfrequencyproducts.com
Registered in England No: 06478545
VAT Registration No: GB932 4502 45
IQD Frequency Products Ltd
Station Road
Crewkerne
Somerset
TA18 8AR
United Kingdom
Tel: +44 (0)1460 270200
Fax: +44 (0)1460 72578
Email: info@iqdfrequencyproducts.com
Registered in England No: 06478545
VAT Registration No: GB932 4502 45
TECHNICAL NOTE 29