S32K310 datasheet(93/137 Pages) NXP

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11.4 Fast External Oscillator (FXOSC)

Table 39. Fast External Oscillator (FXOSC)

Symbol

Description

Min

Typ

Max

Unit

Condition

Spec

Number

FREQ_BYPASS

Input clock

frequency in bypass

mode 1

—

MHz

—

TRF_BYPASS

Input clock rise/fall

time in bypass

mode 1

—

CLKIN_DUTY_

BYPASS

Input clock duty

cycle in bypass

mode 1

47.5

—

52.5

—

FXOSC_CLK

output clock

frequency in crystal

mode

—

MHz

—

TFXOSC

Fxosc start up

time (ALC enabled) 2

—

IFXOSC

Oscillator Analog

circuit supply

current, V25 supply

—

using 8, 16 or 40 MHz

crystal

—

Amplifier

Transconductance

9.7

—

18.5

mA/V

GM_SEL[3:0] =

4`b1111

—

1. For bypass mode applications, the EXTAL pin should be driven low when FXOSC is in off/disabled state.

2. The startup time specification is valid only when the recommended crystal and load capacitors are used. For higher load

capacitances, the actual startup time might be higher.

To ensure stable oscillations, FXOSC incorporates the feedback resistance internally.

Drive level is a crystal specification and if crystal load capacitance is increased beyond the recommended value, it may violate

the crystal drive level rating. In such cases, contact NXP sales representative for selecting the correct crystal.

Crystal oscillator circuit provides stable oscillations when gmXOSC > 5 * gm_crit. The gm_crit is defined as:

gm_crit = 4 * (ESR + RS) * (2πF)2 * (C0 + CL)2

where:

• gmXOSC is the transconductance of the internal oscillator circuit

• ESR is the equivalent series resistance of the external crystal

• RS is the series resistance connected between XTAL pin and external crystal for current limitation

• F is the external crystal oscillation frequency

• C0 is the shunt capacitance of the external crystal

• CL is the external crystal total load capacitance. CL = Cs+ [C1*C2/(C1+C2)]

• Cs is stray or parasitic capacitance on the pin due to any PCB traces

• C1, C2 external load capacitances on EXTAL and XTAL pins

See manufacture datasheet for external crystal component values

Figure 36. Oscillation build-up equation

NXP Semiconductors

Clocking modules

S32K3xx Data Sheet, Rev. 5.2, 10/2022

Data Sheet: Technical Data

Preliminary Information

93 / 137

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