AN2827 datasheet(28/30 Pages) STMICROELECTRONICS

28 / 30 page

Examples of register setup for each mode

AN2827

28/30

Doc ID 15047 Rev 1

Figure 20 provides more details on the timing of the I²C bus packets.

The solution described in Example 5 uses a software termination of the flash pulse (it is

timed out by the internal timer.) The flash pulse could also be terminated by setting the

TRIG pin to low after 4 seconds. In this case, the fourth packet could be the same as

packets 2 and 3, because the timing of the flash is done by the TRIG pin and it is not

necessary to change the value of FTIM in the COMMAND REGISTER.

This method of periodical reloading of the COMMAND REGISTER can be used to achieve a

continuous flash light. However, it is highly recommended to guarantee an efficient cooling

of both the LED and the chip, otherwise the light can be interrupted by activation of the

thermal protections.

Table 29.

4th I²C data packet to restart flash mode

Byte

Hex

Binary

Comment

01100010

Device address + R/W bit

00000000

Command register address

11011010

Data of the command register

Figure 20.

Timing of I²C bus packets for a flash lasting longer than FTIM max

1.0s

1.5s

4.0s

TRIG pin

TRIG_EN bit

I²C bus packets

Timeout of

the first flash

Timeout of

the second

flash

Timeout of

the third flash

Timeout of the

fourth flash –

ending of the

whole flash

pulse

1.5s

1.0s

1.5s

4.0s

TRIG pin

TRIG_EN bit

I²C bus packets

Timeout of

the first flash

Timeout of

the second

flash

Timeout of

the third flash

Timeout of the

fourth flash –

ending of the

whole flash

pulse

1.5s

1.0s

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