AN2708 datasheet(21/42 Pages) STMICROELECTRONICS

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AN2708

High-frequency ballast

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2.2.4

Verification of lamp status

This function detects a lamp disconnection or a lamp failure on the slave board. The

microcontroller performs a double check: one on the PB1 pin for the lamp hardware status

and one on the flag "LAMP_ARC_POWER_ON" for the lamp software status. If the PB1

logical level is low and the flag is true, lamp disconnection happened. The condition is

recorded on ST7FDALI, so when the microcontroller receives a "query frame" from the

master, it changes the PB3 (EN1) and PB4 (EN2) configuration from input to output, and

sends a byte answer as 'STATUS INFORMATION' described below:

●

bit 0 status of ballast; '1'= NOK

●

bit 1 Lamp failure; '1'= NOK

●

bit 2 Lamp arc power on; '0' = OFF

●

bit 3 Query: Limit Error; '0' = Last requested arc power level is between MIN..MAX

LEVEL or OFF

●

bit 4 Fade ready; '0' = fade is ready; '1' = fade is running

●

bit 5 Query: 'RESET STATE'? '0' = 'No'

●

bit 6 Query: Missing short address? '0' = 'No'

●

bit 7 Query: 'POWER FAILURE'? '0' = 'No'; 'RESET' or an arc power control command

has been received after last power-on

When the master receives this frame, it displays the lamp status by means of two LEDs

(green stands for ok, red for status not ok). Once the failure condition has been detected

and solved, an "ON" command has to be sent to the slave, allowing the master's

microcontroller to toggle again the LED status from red to green. From the analog side, to

detect a disconnection or a failure event for each lamp, two signal Schottky diodes have

been used to bias the EN1 or EN2 pin of L6574. The failure condition is detected both at

startup and when running.

The forward and backward frame timing is shown in Figure 12 and 13:

Figure 12.

Forward frame timing

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