Analog front end (AFE)

ST7570

16/26

Doc ID 17526 Rev 2

5.5

Thermal shutdown and temperature control

The ST7570 performs an automatic shutdown of the power amplifier circuitry when the

Moreover, a digital thermometer is embedded to identify the internal temperature among

four zones, as indicated in Table 8.

Table 8.

Temperature zones

5.6

Zero-crossing PLL and delay compensation

In operating mode, ST7570 needs to be synchronized with an external signal period through

zero crossing detection.

The user can select among two input pins for the external zero-crossing reference:

●

Analog input (ZC_IN_A): it requires a bipolar analog input signal which is internally

squared through a Schmidt Trigger comparator with symmetrical thresholds;

●

Digital input (ZC_IN_D): it requires a 50% duty-cycle square-wave digital signal (with

two levels).

The desired input can be selected by accessing a dedicated management information base

(MIB) object.

The ST7570 embeds a phase-locked loop (PLL) to generate the internal reference based on

the external zero-crossing. In case of delay due to external zero crossing coupling circuits

(i.e. based on optocouplers) or to improve interoperability, it is possible to introduce delay

compensation through a dedicated MIB object.

Figure 8.

Zero crossing detection

Temperature zone

Temperature value