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RD-0613

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UVLO Mode and the PFC and ballast oscillators are disabled, the PFC and half-bridge driver outputs

(PFC, LO, and HO) are turned off, and the IRS2168D consumes micro-power current at VCC.

Lamp Removal and Auto-Restart

Resistors RPU, RSD and capacitor CSD1 form a divider/filter network used to detect an open lower

lamp filament and/or lamp replacement. Under normal conditions, the voltage across CSD1 is close to

zero. If the lower filament becomes open or the lamp is removed, however, the voltage at the SD pin

increases above the 5 V threshold and causes the IC to shutdown (Figure 12). The ballast remains

shutdown until a lamp replacement is performed. If the lamp is replaced with a lamp with a good lower

filament, the voltage on the SD pin of the IRS2168D drops back below the 3 V threshold and the

ballast will restart in Preheat Mode. The ballast will go through the Preheat, Ignition, and Run Mode

sequences each time a restart is performed. Note that the SD pin of the IRS2168D is active during

Preheat and Run Modes and is disabled during Ignition Mode.

Fig. 12: SD Pin Voltage (Black) and Lamp Voltage (Blue) during

Lamp Removal/Auto-Restart Condition

Fault Mode

When a fault is detected at the CS pin or SD/EOL pin, the IC will enter Fault Mode. During Fault

Mode, the ballast section and PFC section are both shutdown. The DC bus voltage will drop to the

non-boosted peak AC line voltage level. There are several lamp fault conditions that can cause the IC

to enter into Fault Mode. These include: hard-switching at the half-bridge mid-point (open load), over-

current (non-strike), lamp voltage shift (end-of-life), and lamp removal (SD/EOL pin). Resistor RCS in

the source lead of the low-side MOSFET (MLS) serves as the current-sensing point for the half-bridge,

and is used to detect hard-switching or over-current. During normal operation when the half-bridge is

oscillating, a voltage appears across RCS when the low-side MOSFET, MLS, is turned on. The

magnitude of this voltage directly relates to the current in the lamp resonant circuit.