L6585DETR STMicroelectronics, L6585DETR Datasheet - Page 21

• Manufacturer Part Number: L6585DETR
• Description: IC PFC/BALLAST CONTROL 20-SOIC
• Manufacturer: STMicroelectronics
• Type: PFC/Ballast Controllerr

Specifications of L6585DETR

• Frequency: 58.4 ~ 62 kHz
• Current - Supply: 7mA
• Current - Output: 600mA
• Voltage - Supply: 11 V ~ 16 V
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 20-SOIC (7.5mm Width)
• Switching Frequency: 250 KHz
• Maximum Power Dissipation: 830 mW
• Maximum Operating Temperature: + 150 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8822-2

L6585DE
6.3
Startup sequence with old or damaged lamps
When an old lamp is connected to the ballast the strike voltage is higher than the nominal
voltage and may also be higher than the safety threshold. In this case the lamp can ignite in
a time longer than ignition time or may not ignite. In both cases, during ignition time,
because of the frequency decrease, the voltage at the output of the ballast can easily reach
dangerous values.
The same occurs if the lamp tube is broken: the lamp cannot ignite and the lamp voltage
must be limited.
During ignition time, the L6585DE senses the current flowing into the lamp through a sense
resistor connected to the HBCS pin. If the HBCS pin voltage reaches 1.6 V, a small amount
of current is sunk from the EOI pin causing a small frequency increase. This frequency
modification results, macroscopically, in a frequency regulation and therefore a current
regulation and a lamp voltage limiting.
As soon as the HBCS pin voltage reaches 1.6 V, the TCH pin starts to charge Cd: when the
TCH voltage reaches 4.63 V, the TCH pin is no longer left free (as during preheating), but it
sinks 26 uA, causing a faster discharge of Cd. When the TCH voltage reaches 1.5 V, the pin
is pulled down and HBCS voltage is checked. If it is above 1.05 V the IC is stopped.
If the lamp ignites during this reduced TCH cycle, the EOI pin stops sinking current and if it
reaches 1.9 V, the IC enters run mode and TCH pin is immediately pulled down.
Figure 11. Startup procedures with old or damaged lamps
It can be noted that the reduced TCH cycle time depends only on the value of Cd. It is
suggested to start from the choice of Cd in order to obtain the protection time, and then can
proceed to the choice of Rd to obtain the desired T
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Ballast section
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