L9663 datasheet(22/104 Pages) STMICROELECTRONICS

22 / 104 page

Power supply

L9663

22/104

DocID028693 Rev 1

2.5

Frequency references

The device comes with an integrated accurate oscillator, used for any of the internal

circuitry, with no need of external connections or components. The nominal clock frequency

is 16 MHz with a ±5% accuracy.

Should the application need some more accurate timing reference, a discrete pin CLKIN is

provided. An external clock reference can be connected to this pin. The PSI5 transceiver IC

offers an integrated FLL module that tracks this input to provide a high accurate clock

reference (±1%). This feature can be used especially if accurate timeslot control needs to be

achieved.

External signal on CLKIN can be configured as follows (see CLKIN_CFG bits in GCR1 SPI



1 MHz square signal



4 MHz square signal



No signal (Not connected pin)

Pin CLKIN can be grounded when not used. The pin input circuit implements a pull-down

structure.

The FLL module tracking the CLKIN signal is off by default.

The PSI5 transceiver IC implements a safety function for monitoring the device clock

reference, both in case it is derived from the CLKIN signal through the FLL module or

internally generated. In the first condition the monitoring is always activated, while in the

second condition it can be enabled by programming in ST (storing a '1' in a dedicated

OTP(c) bit) and another oscillator generator is used for monitoring.(d)

When the CLKIN_CFG is set, the FLL tries to close the LOOP and a mask counter of

T_CKMSK (16 ms MAX) is used to count the maximum transient time.

During this time, regardless the CLK frequency the CKER_DETECT is masked, i.e the

device doesn't detect a clock error.

After this time, if the CLKIN frequency is in the correct range, the loop is closed and the CLK

frequency is inside the 1% tolerance; if the CLKIN frequency is outside the malfunction

detecting range, a clock error is detected after a detection time T_CKERD, the device is

reset and the CLK_FLT is set so that the μC can read the reset source.

The T_CKERD and the transient during detection time depend on the CLKIN frequency

behavior; the figure below shows the behavior of the internal oscillator as function of the

external one.

c. One Time Programmable bit: it can be programmed by ST only.

d. For clock error detection by internal monitor oscillator see errata n.3367, Section 7: Errata.

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