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AM4376 Datasheet(PDF) 134 Page - Texas Instruments |
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AM4376 Datasheet(HTML) 134 Page - Texas Instruments |
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134 / 261 page  Device RTC_XTALIN RTC_XTALOUT C 1 C 2 Optional R bias Optional R d Crystal VSS_RTC AM4376, AM4377, AM4378, AM4379 SPRS851B – JUNE 2014 – REVISED APRIL 2015 www.ti.com 5.12.2.3.3 OSC1 Internal Oscillator Clock Source Figure 5-13 shows the recommended crystal circuit for OSC1 of the package. It is recommended that pre- production printed circuit board (PCB) designs include the two optional resistors Rbias and Rd in case they are required for proper oscillator operation when combined with production crystal circuit components. In most cases, Rbias is not required and Rd is a 0-Ω resistor. These resistors may be removed from production PCB designs after evaluating oscillator performance with production crystal circuit components installed on pre-production PCBs. The RTC_XTALIN terminal has a 10 - 40 k Ω internal pullup resistor which is enabled when OSC1 is disabled. This internal resistor prevents the RTC_XTALIN terminal from floating to an invalid logic level which may increase leakage current through the oscillator input buffer. A. Oscillator components (Crystal, C1, C2, optional Rbias and Rd) must be located close to the 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 RTC_XTALIN and RTC_XTALOUT signals. For recommended values of crystal circuit components, see Table 5-16. Figure 5-13. OSC1 Crystal Circuit Schematic Table 5-16. OSC1 Crystal Circuit Requirements NAME DESCRIPTION MIN TYP MAX UNIT Crystal parallel resonance Fundamental mode oscillation only 32.768 kHz frequency Crystal frequency stability Maximum RTC error = 10.512 minutes -20.0 20.0 fxtal ppm and tolerance per year Maximum RTC error = 26.28 minutes per -50.0 50.0 ppm year CC1 C1 capacitance 12.0 24.0 pF CC2 C2 capacitance 12.0 24.0 pF Cshunt Shunt capacitance 1.5 pF Crystal effective series fxtal = 32.768 kHz, oscillator has nominal 80 ESR resistance negative resistance of 725 k Ω and worst- k Ω case negative resistance of 250 k Ω Table 5-17. OSC1 Crystal Circuit Characteristics NAME DESCRIPTION MIN TYP MAX UNIT Shunt capacitance of ZDN package 0.17 Cpkg pF package 134 Specifications Copyright © 2014–2015, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: AM4376 AM4377 AM4378 AM4379 |
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