ST52T400 datasheet(66/94 Pages) STMICROELECTRONICS

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10.3 Burst Mode

When working in Burst mode, the synchronization

with

the

mains

mandatory,

therefore

REG_CONF10(4) bit CKSL must be set to “1”.

(Table 10.3).

A square wave Tb is generated with a duty cycle

proportional to the power the user needs to trans-

fer to the load. A pulse is generated for each zero

crossing of the mains voltage included in the Ton

of the fixed period T. Figure 10.4 illustrates the

typical Burst Control working mode. The period T

of the signal Tb (Figure 10.4) is:

T = 255*Tck

The signal Tck is generated by programming the

16-bit

Prescaler

REG_CONF8

and

REG_CONF9 (Figure 10.2). Tck is equal to the

mains voltage frequency (50 or 60 Hz) divided by

N+1, where N is an integer value in the range [0,

216-1].

The value Ton is proportional to the value con-

tained in TRIAC_COUNT Register (Output Regis-

ter 9)

The number of generated pulses N_PULSES in

TROUT pin is equal to:

N_PULSES = 2*[(N+1)*TRIAC_COUNT]

where N is the value stored in the 16-bit prescaler.

Therefore it is:

Ton = TRIAC_COUNT*Tck

The TRIAC_COUNT can be changed on fly and

takes effect from the following period; the Pres-

caler value N instead is fixed since the beginning

and cannot be changed on fly.

The first pulse is obtained during the first zero

crossing of the main voltage and the last one is

generated after clock pulses included in the time

period TRIAC_COUNT*Tck, where Tck is the

Prescaler output, generated by using the main

voltage frequency applied to MAIN1 and MAIN2

pins. This guarantees synchronization with the

mains voltage frequency.

Ranges of the Tb signal period depend on the

power line frequency and Prescaler (Table 10.2).

In order to drive a Triac in Burst Mode a pulse

sequence must be generated, which must be cen-

tered on the zero crossing of the power line as

illustrated in Figure 10.7. Therefore, the pre zero

crossing and the post zero crossing of the power

line must be detected.

To detect the zero-crossing and also obtain the

main voltage frequency, the user must generate

MAIN1 and MAIN2 signals by using the circuit

illustrated in Figure 10.5.

MAIN1 and MAIN2 signals are used in the block

called PULSE GENERATOR of the peripheral

(see Figure 10.1).

Table 10.2 TROUT Signal Period

Power Line

Frequency

min

max

50 Hz

5.10 s

334233.60 s

60 Hz

4.25 s

278528.05 s

Figure 10.4 Burst Working Mode

-1.5

-1

-0.5

0.5

1.5

Ton

Power

Line

T = 255 * Tck

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