PT7C4311 Datasheet, PDF (6/16 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4311
Real-time Clock Module (I²C Bus)
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Recommended Layout for Crystal
Note: The crystal, traces and crystal input pins
should be isolated from RF generating signals.
Built-in Capacitors Specifications and Recommended External Capacitors
Parameter
Symbol
Typ
Unit
Build-in capacitors
X1 to GND
X2 to GND
C_G
C_D
18
18
pF
pF
Recommended External
X1 to GND
C₁
8
pF
capacitors
X2 to GND
C₂
8
pF
Note: The frequency of crystal can be optimized by external capacitor C₁ and C₂, for frequency=32.768Hz, C₁ and C₂ should meet
the equation as below:
Cpar + [(C₁+C_G)*(C₂+C_D)]/ [(C₁+C_G)+(C₂+C_D)] =C_L
Cpar is all parasitical capacitor between X1 and X2.
C_L is crystal’s load capacitance.
Crystal Specifications
Parameter
Symbol
Min
Typ
Max
Unit
Nominal Frequency
f_O
-
32.768
-
kHz
Series Resistance
ESR
-
-
70
k
Load Capacitance
C_L
-
12.5
-
pF
2015-06-0002
PT0322-8
06/16/15
6