ST52T400 datasheet(67/94 Pages) STMICROELECTRONICS

67 / 94 page

ST52T400/T440/E440/T441

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In particular, the pulses are generated by using

the rising edge of the signal MAIN1 and the falling

edge of the signal MAIN2. Figure 10.6 illustrates

the generation of the Triac pulses Tp.

The first firing pulse for the Triac is generated on

the zero crossing of the power line, while the next

pulses are centered on the zero crossing. Gener-

ally, the Triac firing pulses start 1/2 Tp before the

zero crossing and the length of the pulses is Tp,

see Figure 10.6.

The length Tp of the pulses is programmable by

using

bit

value

UTP,

obtained

with

REG_CONF19

bits,

UTPMSB,

and

REG_CONF20, UTPLSB (see Figure 10.12 and

Table 10.5):

TP =TCLKM *UTP

The value Tp is in the range [0, 3.2]

ms when the

clock master is 20 MHz.

According to REG_CONF10(0) configuration reg-

ister bit, POL, the firing pulses polarity may be set;

in order to obtain positive or negative gate Triac

currents, allowing to work respectively in I and IV

quadrants, or in the II and III quadrants (see Fig-

ure 10.6).

The pulses polarity can be changed on fly with

immediate effect.

Working in the II and III quadrant the peripheral

implements the following procedure:

1) The firing pulse is set to “1" on the rising edge

Figure 10.5 Burst Mode Zero Crossing Circuit

Figure 10.6 Burst Mode Zero Crossing Circuit

(1)

(0.5)

0.5

Negative

Triac Gate

Current

½Tp

Positive

Triac Gate

Current

Power

Line

II and III quadrants

I and IV quadrants

½Tp

Figure 10.7 Burst Mode Zero Crossing

MAIN1

MAIN2

-1.5

-1

-0.5

0.5

Main Voltage

TRIACOUT

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