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ST7538

Zero Crossing Detection

The Mains Voltage Zero Crossing can be detected, through a proper connection of ZCIN to the Mains.

ZCIN comparator has a threshold fixed at SGND. ZCOUT is a TTL Output forced High after a positive

zero-crossing transition, and low after a negative one.

Setting the Bit 11 inside the Control Register to “1” the transmission is automatically synchronized to the

mains positive zero-crossing transition. This function is achieved turning on the PLI when RX/TX is low

and delaying the CLR/T first transition until the first zero-crossing event. The automatic synchronization

procedure can work only if the synchronous interface is programmed. If asynchronous interface is in use

the Zero Crossing synchronization can be achieved managing the ZCOUT line.

Figure 19. Synchronous Zero-Crossing Transmission

Output Clock

MCLK is the master clock output. The clock frequency sourced can be programed through the control reg-

ister to be a ratio of the crystal oscillator frequency (Fosc, Fosc/2 Fosc/4). The transition between one fre-

quency and another is done only at the end of the ongoing cycle.

Reg OK

REGOK allows to detect an undesired modification of the control register content. REGOK function is dis-

abled during a control register writing session.

Under Voltage Lock Out

The UVLO function turns off the device if the PAVdd voltage falls under 4V. Hysteresis is 340mV typically.

Thermal Shutdown

The ST7538 is provided of a thermal protection which turn off the PLI when the junction temperature ex-

ceeds 170°C ±10% . Hysteresis is around 30°C.

When shutdown threshold is overcome, PLI interface is switched OFF.

Thermal Shutdown event is notified to the HOST controller using TIMEOUT line. When TIMEOUT line is

High, ST7538 junction temperature exceed the shutdown threshold (Not Lached).

5V Voltage Regulator and Power Good Function

ST7538 has an embedded 5V linear regulator externally available to supply the application circuitry.

The linear regulator has a very low quiescent current (50

µA) and a current capability of 100mA. The reg-

ulator is protected against short circuitry events.

t

ZCIN

RxTx

CLR/T

TxD

ZCOUT

D03IN1423