43.14 XOSC32 AC Electrical Specifications

Table 43-18. XOSC32 AC Electrical Specifications
AC CharacteristicsStandard Operating Conditions: VDD = 1.9V to 3.6V (unless otherwise stated) Operating Temperature: -40°C ≤ TA ≤ +85°C for Industrial Temp -40°C ≤ TA ≤ +125°C for Extended Temp
Param. No.SymbolCharacteristicsMin.Typ.Max.UnitsConditions(1)
XOSC32_1FOSC_XOSC32XOSC32 oscillator crystal frequency32.764kHzXIN32, XOUT32 secondary oscillator
XOSC32_3CXIN32XOSC32 XIN32 parasitic pin capacitance0.4pF

0.4 pF at the SOC pins and

2.4 pF on the WBZ35x Module

2.4
XOSC32_5CXOUT32XOSC32 XOUT32 parasitic pin capacitance0.4pF

0.4 pF at the SOC pins and

2.4 pF on the WBZ35x Module

2.4
XOSC32_11CLOAD_X32(4) 32.768 kHz crystal load capacitance11pF
XOSC32_13ESR_X32 32.768 kHz crystal ESR75100kΩ
XOSC32_15TOSC32TOSC32 = 1/FOSC_XOSC3230.5µsSee parameter XOSC32_1 for FOSC_XOSC32 value
XOSC32_17XOSC32_ST(3)XOSC32 crystal start-up time 1024TOSCCrystal stabilization time only not oscillator ready
Note:
  1. VDDIO = AVDD = 3.3V.
  2. The parameters are characterized but not tested in manufacturing.
  3. This is for guidance only. A major component of crystal start-up time is based on the second party crystal MFG parasitic that is outside the scope of this specification. If this is a major concern, the customer might need to characterize this based on their design choices.
  4. The test conditions for the crystal load capacitor calculation are as follows:
    • Standard PCB trace capacitance = 1.5 pF per 12.5 mm (0.5 inches) (in other words, PCB STD TRACE W = 0.175 mm, H = 36 μm, T = 113 μm)
    • Xtal PCB capacitance typical; therefore, ~= 2.5 pF for a tight PCB xtal layout
    • For CXIN and CXOUT within 4 pF of each other, assume CXTAL_EFF = ((CXIN / 2)
    • Note: Averaging CXIN and CXOUT will affect the final calculated CLOAD value by less than the tolerance of the capacitor selection.
    Equation 1:
    MFGCLOADSpec={([CXIN+C1]*[CXOUT+C2])/[CXIN+C1+C2+CXOUT]}+estimatedoscillatorPCBstraycapacitance

    Assuming C1 = C2 and CXin ~= CXout, the formula can be further simplified and restated to solve for C1 and C2 by:

    Equation 43-3. Equation 2 (In other words: Simplified Equation 1)
    C1=C2=((2*MFGCLOADSpec)CXTAL_EFF(2*PCBcapacitance))

    Example:

    • XTAL Mfg CLOAD Data Sheet Spec = 12 pF
    • PCB XTAL trace Capacitance = 2.5 pF
    • CXIN pin = 6.5 pF, CXOUT pin = 4.5 pF therefore CXTAL_EFF = ((CXIN / 2)

    CXTAL_EFF = ((6.5 + 4.5)/2) = 5.5 pF

    C1 = C2 = ((2 * MFG Cload spec) – CXTAL_EFF – (2 * PCB capacitance))

    C1 = C2 = (24 – 5.5 – (2 * 2.5))

    C1 = C2 = (24 – 5.5 – 5)

    C1 = C2 = 13.5 pF (Always rounded down)

    C1 = C2 = 13 pF (in other words, for hypothetical example crystal external load capacitors)

    User C1 = C2 = 13 pF ≤ CLOAD_X32 (max.) spec

  5. User selectable in OSC32KCTRL.STARTUP.
Figure 43-2. XOSC32 Block Diagram