CY28442 Cypress Semiconductor, CY28442 Datasheet - Page 10

• Manufacturer Part Number: CY28442
• Description: Clock Generator
• Manufacturer: Cypress Semiconductor

Document #: 38-07680 Rev. **
As mentioned previously, the capacitance on each side of the
crystal is in series with the crystal. This mean the total capac-
itance on each side of the crystal must be twice the specified
load capacitance (CL). While the capacitance on each side of
the crystal is in series with the crystal, trim capacitors
(Ce1,Ce2) should be calculated to provide equal capacitance
loading on both sides.
Use the following formulas to calculate the trim capacitor
values for Ce1 and Ce2.
CLe
Total Capacitance (as seen by the crystal)
=
(
Load Capacitance (each side)
Ce1 + Cs1 + Ci1
Ce = 2 * CL – (Cs + Ci)
1
+
1
Ce2 + Cs2 + Ci2
Cs1
ADVANCE INFORMATION
1
Figure 2. Crystal Loading Example
Ce1
X1
Ci1
Clock Chip
)
XTAL
Ci2
CL ....................................................Crystal load capacitance
CLe ......................................... Actual loading seen by crystal
using standard value trim capacitors
Ce ..................................................... External trim capacitors
Cs ..............................................Stray capacitance (terraced)
Ci .......................................................... Internal capacitance
(lead frame, bond wires etc.)
CL ....................................................Crystal load capacitance
CLe ......................................... Actual loading seen by crystal
using standard value trim capacitors
Ce ..................................................... External trim capacitors
Cs ..............................................Stray capacitance (terraced)
Ci .......................................................... Internal capacitance
(lead frame, bond wires etc.)
X2
Ce2
Cs2
3 to 6p
33pF
Pin
Trim
Trace
2.8pF
CY28442
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