S35390A Datasheet, PDF (39/51 Pages) Seiko Instruments Inc – FOR AUTOMOTIVE 105C OPERATION

Rev.2.2_00
FOR AUTOMOTIVE 105°C OPERATION 2-WIRE REAL-TIME CLOCK
S-35390A H Series
 Adjustment of Oscillation Frequency
1. Configuration of crystal oscillation circuit
Since the crystal oscillation circuit is sensitive to external noise (the clock accuracy is affected), the following measures
are essential for optimizing the configuration.
• Place the S-35390A H Series crystal oscillator, and external capacitor (C_g) as close to each other as possible.
• Increase the insulation resistance between pins and the substrate wiring patterns of XIN and XOUT.
• Do not place any signal or power lines close to the crystal oscillation circuit.
• Locating the GND layer immediately below the crystal oscillation circuit is recommended.
• Locate the bypass capacitor adjacent to the power supply pin of the S-35390A H Series.
Parasitic capacitance^*3
XIN
Cg
Crystal oscillator: 32.768 kHz
CL = 6 pF^*1
Cg = None^*2 to 9.1 pF
Parasitic capacitance^*3
XOUT
Cd
Rf
Rd
Rf = 100 M (typ.)
Rd = 100 k (typ.)
Cd = 8 pF (typ.)
S-35390A H Series
*1. When setting the value for the crystal oscillator's C_L as 7 pF, connect C_d externally if necessary.
*2. The crystal oscillation circuit operates even when C_g is not connected. Note that the oscillation frequency is in the
direction that it advances.
*3. Design the board so that the parasitic capacitance is within 5 pF.
Figure 49 Connection Diagram 1
Crystal
oscillator
C_g
1
S-35390A H ₈
2 XOUT ^Series
7
3 XIN
6
4 ^VSS
5
Locate the GND layer in the
layer immediately below
Figure 50 Connection Diagram 2
Caution
1. When using the crystal oscillator with a C_L exceeding the rated value (7 pF) (e.g: C_L = 12.5 pF),
oscillation operation may become unstable. Use a crystal oscillator with a C_L value of 6 pF or 7 pF.
2. Oscillation characteristics is subject to the variation of each component such as substrate parasitic
capacitance, parasitic resistance, crystal oscillator, and C_g. When configuring a crystal oscillation
circuit, pay sufficient attention for them.
Seiko Instruments Inc.
39