MCP795W10-I/SL Microchip Technology, MCP795W10-I/SL Datasheet - Page 37

• Manufacturer Part Number: MCP795W10-I/SL
• Description: SPI GPP RTCC, 1Kb EE, 64B SRAM, WD Timer, Event Detect, ID 14 SOIC .150in TUBE
• Manufacturer: Microchip Technology

9.2
The MCP795XXX has been designed to operate with a
standard 32.768 kHz tuning fork crystal. The on-board
oscillator has been characterized to operate with a
crystal of maximum ESR of 70K Ohms.
Crystals with a comparable specification are also suit-
able for use with the MCP795XXX.
The table below is given as design guidance and a
starting point for crystal and capacitor selection.
EQUATION 9-1:
The following must also be taken into consideration:
• Pin capacitance (to be included in Cx2 and Cx1)
• Stray Board Capacitance
The recommended board layout for the oscillator area
is shown in
crystal and the load capacitors. In this example, C2 is
CX1, C1 is CX2 and the crystal is designated as Y1.
When calculating the effective load capacitance,
Equation 9-1
FIGURE 9-9:
 2011-2012 Microchip Technology Inc.
Micro Crystal
Citizen
Please work with your crystal vendor.
Manufacturer
Crystal Specification and
Selection
C
Figure
can be used.
load
=
9-9. This actual board shows the
-----------------------------
CX2
CX2 CX1
BOARD LAYOUT
CM7V-T1A
CM200S-32.768KDZB-UT
+

CX1
Part Number
+
C
stray
MCP795WXX/MCP795BXX
Preliminary
7pF
6pF
Capacitance
Crystal
Gerber files are available on request. Please contact
your Microchip Sales representative.
It is required that the final application should be tested
with the chosen crystal and capacitor combinations
across all operating and environmental conditions.
Please also consult with the crystal specification to
observe correct handling and reflow conditions and for
information on ideal capacitor values.
For more information please see the RTCC Best
Practices AN1365 (DS01365).
10pF
10pF
CX1 Value
12pF
8 pF
DS22280B-page 37
CX2 Value