DRA722_17 Datasheet, PDF (182/408 Pages) Texas Instruments – Infotainment Applications Processor

DRA722, DRA724, DRA725, DRA726
SPRS956B – MARCH 2016 – REVISED JANUARY 2017
Device
rtc_osc_xi_clkin32
rtc_osc_xo
Crystal
Rd
(Optional)
C_f1
C_f2
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SPRS906_CLK_01
Figure 6-10. Crystal Implementation
NOTE
The load capacitors, C_f1 and C_f2 in Figure 6-10, should be chosen such that the below
equation is satisfied. C_L in the equation is the load specified by the crystal manufacturer. All
discrete components used to implement the oscillator circuit should be placed as close as
possible to the associated oscillator rtc_osc_xi_clkin32 and rtc_osc_xo pins.
CL=
C C _{f1 f2}
(C_f1+C_f2)
Figure 6-11. Load Capacitance Equation
The crystal must be in the fundamental mode of operation and parallel resonant. Table 6-9 summarizes
the required electrical constraints.
Table 6-9. RTC Crystal Electrical Characteristics
NAME
f_p
C_f1
C_f2
ESR(C_f1,C_f2)
C_O
L_M
C_M
t_{j(rtc_osc_xi_clkin32)}
DESCRIPTION
Parallel resonance crystal frequency
C_f1 load capacitance for crystal parallel resonance with C_f1 = C_f2
C_f2 load capacitance for crystal parallel resonance with C_f1 = C_f2
Crystal ESR
Crystal shunt capacitance
Crystal motional inductance for f_p = 32,768 kHz
Crystal motional capacitance
Frequency accuracy, rtc_osc_xi_clkin32
MIN
TYP
32.768
12
12
10.7
2.2
MAX
24
24
80
5
±200
UNIT
kHz
pF
pF
kΩ
pF
mH
fF
ppm
When selecting a crystal, the system design must take into account the temperature and aging
characteristics of a crystal versus the user environment and expected lifetime of the system.
Table 6-10 details the switching characteristics of the oscillator and the requirements of the input clock.
NAME
f_p
Table 6-10. Oscillator Switching Characteristics—Crystal Mode
DESCRIPTION
Oscillation frequency
MIN
TYP
32.768
MAX
UNIT
kHz
182 Clock Specifications
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