Oscillator Circuit; Others Precautions - Epson S2R72A21 Application Note

7.3

Oscillator circuit

Please connect the Crystal oscillator (24MHz) as following. Epson recommends the frequency accuracy within
±100ppm in order to realize a high quality waveform.
Recommended part (Automotive quality): FA-238A (CL=7pF) by Seiko Epson Corp.
Regarding the amount of Cg, Cd and Rd, please decide by evaluating the matching based on the actual boards.
For your reference, Epson's evaluation board's constants are Cg=6[pF], Cd=7[pF], Rd=0[Ω]
7.4

Others precautions

•
Resistance connected to the R1 pin
A 6.04 kΩ ±1% resistance should be positioned as close as possible to the R1 pin. This is used to generate the
standard reference current which determines the USB analog circuit characteristics, so the analog characteristics
will be affected if the tolerances are overly large. A resistance with the specified accuracy must always be used.
•
FVDD pin, LVDDC pin, LVDDM pin
Each of these 3 pins needs 0.1uF and 10uF capacitors to be placed between the VSS. These capacitors should be
mounted as close as possible to these pins in order of 0.1uF and 10uF from pin.
Figure 7.4.1
•
HVDD pins
Epson recommends placing the
amount on Epson's evaluation board is as following, but it would vary depending on the regulator's
characteristics. Epson also recommends this to be assembled towards each power supply pin to ensure a stable
IC's operation.
S2R72A21 Application Note
(Rev.1.00)
XI
Cg
Figure 7.3.1 Typical crystal oscillator connection circuit
FVDD
0.1uF
10uF
FVDD pin, LVDDC pin, LVDDM pin (Placement of capacitor)
Bypass capacitors as close as possible to each HVDD pin. The capacitance
Seiko Epson Corporation
S2R72A21
Built-in 1M ohm
XO
Rd
Xtal
Cd
S2R72A21
LVDDC LVDDM
0.1uF
0.1uF
10uF 10uF
29