SPC574K72E5 datasheet(48/127 Pages) STMICROELECTRONICS

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Electrical characteristics

SPC574Kxx

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DocID023601 Rev 5

3.10.2

External oscillator (XOSC)

Table 24. External Oscillator electrical specifications

Symbol

Parameter

Conditions

Value

Unit

Min

Max

fXTAL

D Crystal Frequency

Range(1)

—4

MHz

—>8

—>20

tcst

T Crystal start-up time (2),(3)

TJ = 150 °C

—

trec

CC — Crystal recovery time(4)

——

0.5

VIHEXT

D EXTAL input high voltage

(External Reference)

VREF = 0.28 * VDD_HV_IO_JTAG

VREF +

0.6

—V

VILEXT

D EXTAL input low voltage(5) VREF = 0.28 * VDD_HV_IO_JTAG

—VREF - 0.6

CS_EXTAL CC T Total on-chip stray

capacitance on EXTAL

pin(6)

QFP

6.0

8.0

CS_XTAL

T Total on-chip stray

capacitance on XTAL pin(8)

QFP

6.0

8.0

P Oscillator

Transconductance

TJ = -40 °C to

150 °C

4.5 V < VDD_HV

_IO < 5.5 V

fXTAL  8 MHz

2.6

11.0

mA/V

CfXTAL  20 MHz

7.9

26.0

CfXTAL  40 MHz

10.4

34.0

VEXTAL

D Oscillation Amplitude on

the EXTAL pin after

startup(7)

TJ = –40 °C to 150 °C

0.5

1.8

VHYS

D Comparator Hysteresis

TJ = 150 °C

0.1

1.0

IXTAL

D XTAL current(8)

TJ = 150 °C

—

The range is selectable by UTEST miscellaneous DCF clients XOSC_LF_EN and XOSC_EN_40 MHz.

This value is determined by the crystal manufacturer and board design.

Proper PC board layout procedures must be followed to achieve specifications.

Crystal recovery time is the time for the oscillator to settle to the correct frequency after adjustment of the integrated load

capacitor value.

Applies to an external clock input and not to crystal mode.

See crystal manufacturer’s specification for recommended load capacitor (CL) values.The external oscillator requires

external load capacitors when operating from 8 MHz to 16 MHz. Account for on-chip stray capacitance (CS_EXTAL/CS_XTAL)

and PCB capacitance when selecting a load capacitor value. When operating at 20 MHz/40 MHz, the integrated load

capacitor value is selected via S/W to match the crystal manufacturer’s specification, while accounting for on-chip and PCB

capacitance.

Amplitude on the EXTAL pin after startup is determined by the ALC block, i.e., the Automatic Level Control Circuit. The

function of the ALC is to provide high drive current during oscillator startup, but reduce current after oscillation in order to

reduce power, distortion, and RFI, and to avoid over-driving the crystal. The operating point of the ALC is dependent on the

crystal value and loading conditions.

IXTAL is the oscillator bias current out of the XTAL pin with both EXTAL and XTAL pins grounded. This is the maximum

current during startup of the oscillator. The current after oscillation is typically in the 2-3 mA range and is dependent on the

load and series resistance of the crystal. Test circuit is shown in Figure 12. The ALC block is the Automatic Level Control

Circuit. The function of the ALC is to provide high drive current during oscillator startup, but reduce current after oscillation

in order to reduce power, distortion, and RFI, and to avoid overdriving the crystal.

SPC574K72E5 Datasheet(PDF) 48 Page - STMicroelectronics

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