ST HTSSOP38, Manual

Page: 26 / 73

Functional description L6482
26/73 Doc ID 023768 Rev 1
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 (C
L
)
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)
1. First harmonic resonance frequency.
C
L
(2)
2. Lower ESR value allows greater load capacitors to be driven.
8 MHz 25 pF (ESR
max
= 80
Ω
)
16 MHz 18 pF (ESR
max
= 50
Ω
)
24 MHz 15 pF (ESR
max
= 40
Ω
)
32 MHz 10 pF (ESR
max
= 40
Ω
)