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AM3359 Datasheet(PDF) 96 Page - Texas Instruments |
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AM3359 Datasheet(HTML) 96 Page - Texas Instruments |
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96 / 162 page  AM335x RTC_XTALIN RTC_XTALOUT C 1 C 2 Optional R bias Optional R d Crystal AM3359, AM3358, AM3357 AM3356, AM3354, AM3352 SPRS717 – OCTOBER 2011 www.ti.com A. Oscillator components (Crystal, C1, C2, optional Rbias and Rd) must be located close to the AM335x package. Parasitic capacitance to the printed circuit board (PCB) ground and other signals should be minimized to reduce noise coupled into the oscillator. B. C1 and C2 represent the total capacitance of the respective PCB trace, load capacitor, and other components (excluding the crystal) connected to each crystal terminal. The value of capacitors C1 and C2 should be selected to provide the total load capacitance, CL, specified by the crystal manufacturer. The total load capacitance is CL = [(C1*C2)/(C1+C2)] + Cshunt, where Cshunt is the crystal shunt capacitance (C0) specified by the crystal manufacturer plus any mutual capacitance (Cpkg + CPCB) seen across the AM335x RTC_XTALIN and RTC_XTALOUT signals. For recommended values of crystal circuit components, see Table 4-2. Figure 4-8. OSC1 Crystal Circuit Schematic Table 4-2. OSC1 Crystal Circuit Requirements NAME DESCRIPTION MIN TYP MAX UNIT fxtal Crystal parallel resonance Fundamental mode oscillation only 32.768 kHz frequency Crystal frequency Maximum RTC error = 10.512 -20.0 20.0 ppm stability/tolerance minutes/year Maximum RTC error = 26.28 -50.0 50.0 ppm minutes/year CC1 C1 capacitance 12.0 24.0 pF CC2 C2 capacitance 12.0 24.0 pF Cshunt Shunt capacitance 5.0 pF ESR Crystal effective series fxtal = 32.768 kHz, oscillator has nominal 80 k Ω resistance negative resistance of 725 k Ω and worst-case negative resistance of 250 k Ω 4.2.2.4 OSC1 LVCMOS Digital Clock Source Figure 4-9 shows the recommended oscillator connections when OSC1 is connected to an LVCMOS square-wave digital clock source. The LVCMOS clock source is connected to the RTC_XTALIN terminal. In this mode of operation, the RTC_XTALOUT terminal should not be used to source any external components. The printed circuit board design should provide a mechanism to disconnect the RTC_XTALOUT terminal from any external components or signal traces that may couple noise into OSC1 via the RTC_XTALOUT terminal. The RTC_XTALIN terminal does not enable an internal pull-down resistor when OSC1 is disabled. If this oscillator is disabled, the RTC_XTALIN terminal may float to an invalid logic level which may increase leakage current through the oscillator input buffer. This should not be an issue for most applications that use this oscillator to source the RTC clock since the RTC requires a continuous clock to maintain time. 96 Power and Clocking Copyright © 2011, Texas Instruments Incorporated Submit Documentation Feedback www.ti.com: AM3359 AM3358 AM3357 AM3356 AM3354 AM3352 |
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