L6482 datasheet(26/73 Pages) STMICROELECTRONICS

26 / 73 page

Functional description

L6482

26/73

Doc ID 023768 Rev 2

6.8

Internal oscillator and oscillator driver

The control logic clock can be supplied by the internal 16-MHz oscillator, an external

oscillator (crystal or ceramic resonator) or a direct clock signal.

These working modes can be selected by EXT_CLK and OSC_SEL parameters in the

CONFIG register (see Table 35).

At power-up the device starts using the internal oscillator and provides a 2-MHz clock signal

on the OSCOUT pin.

Attention:

In any case, before changing clock source configuration, a

hardware reset is mandatory. Switching to different clock

configurations during operation may cause unexpected

behavior.

6.8.1

Internal oscillator

In this mode the internal oscillator is activated and OSCIN is unused. If the OSCOUT clock

source is enabled, the OSCOUT pin provides a 2, 4, 8 or 16-MHz clock signal (according to

OSC_SEL value); otherwise it is unused (see Figure 12).

6.8.2

External clock source

Two types of external clock source can be selected: crystal/ceramic resonator or direct clock

source. Four programmable clock frequencies are available for each external clock source:

8, 16, 24 and 32-MHz.

When an external crystal/resonator is selected, the OSCIN and OSCOUT pins are used to

drive the crystal/resonator (see Figure 12). The crystal/resonator and load capacitors (CL)

must be placed as close as possible to the pins. Refer to Table 8 for the choice of the load

capacitor value according to the external oscillator frequency.

If a direct clock source is used, it must be connected to the OSCIN pin and the OSCOUT pin

supplies the inverted OSCIN signal (see Figure 12).

The L6482 integrates a clock detection system that resets the device in the case of a failure

of the external clock source (direct or crystal/resonator). The monitoring of the clock source

is disabled by default, it can be enabled setting high the WD_EN bit in the GATECFG1

Table 8.

CL values according to external oscillator frequency

Crystal/resonator frequency (1)

First harmonic resonance frequency.

(2)

Lower ESR value allows greater load capacitors to be driven.

8 MHz

25 pF (ESRmax = 80 Ω)

16 MHz

18 pF (ESRmax = 50 Ω)

24 MHz

15 pF (ESRmax = 40 Ω)

32 MHz

10 pF (ESRmax = 40 Ω)

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