JAJSLW7B December 2020 – September 2023 TPS6593-Q1
PRODUCTION DATA
A crystal oscillator can be used for application requiring a high accuracy real-time clock module. The OSC32KCAP pin is bypassed with a 100-nF bypass capacitor for noise rejection. For the OSC32KIN and OSC32KOUT pins, a simplified oscillator schematic is shown in Figure 9-2 to determine what external load capacitors are needed for the crystal.
CIN1 and CIN2 are both 12-pF for this device. CPCB1 and CPCB2 depend on the board but is generally around 1-pF. The crystal oscillator chosen must have a required load capacitance of either 6-pF, 9-pF, or 12.5-pF and the value of the XTAL_SEL bit in the RTC_CTRL_2 register must be updated based on the oscillator chosen. To achieve the required load capacitance (CL) for the oscillator, Equation 25 is used. This equation assumes that the crystal series capacitance is negligible.
Assuming CL1 = CL2, this simplifies to CL1 = 2 × CL - CPCB - CIN. Simplifying this into the standard capacitor values typically available results in the following general capacitor recommendations. If more precise matching is desired, complete the exercise without series capacitance neglected and with exact PCB parasitic capacitance. Too much capacitance results in a lower than expected oscillator frequency, while not enough capacitance has the opposite impact.
Crystal CL (pF) | Component CL1 = CL2 (pF) |
---|---|
6 | 0 |
9 | 6 |
12.5 | 12.5 |
The recommended components using a 9-pF oscillator as an example are in Table 9-4. If an alternate load capacitance crystal is used, the values of the load capacitors must be adjusted to match based on the above.
Component | MANUFACTURER | PART NUMBER | VALUE | EIA size code | SIZE (mm) | Used for Validation |
---|---|---|---|---|---|---|
Capacitor | Murata | GCM155R71C104JA55D | 100-nF, 16-V, X7R | 0402 | 1.0 x 0.5 | Yes |
Capacitor | TDK | CGA2B1X7R1C104K050BC | 100-nF, 16-V, X7R | 0402 | 1.0 x 0.5 | - |
Crystal | NDK | NX3215SD-32.768K-STD-MUS-6 | 32.768-kHz, ±20 ppm, 9-pF | 3.2 x 1.5 x 0.9 | Yes | |
Crystal | Abracon | ABS07AIG-32.768kHz-9-T | 32.768-kHz, ±20 ppm, 9-pF | 3.2 x 1.5 x 0.9 | - | |
Capacitor | Murata | GCM1555C1H6R0CA16 | 6-pF, 50-V, C0G/NP0 | 0402 | 1.0 x 0.5 | Yes |
Capacitor | TDK | CGA2B2C0G1H060D050BA | 6-pF, 50-V, C0G/NP0 | 0402 | 1.0 x 0.5 | - |