ꢀꢁꢁ ꢂ ꢃꢄ ꢅ ꢆ ꢀꢁꢁ ꢂ ꢃꢄ ꢇ ꢆ ꢀ ꢁꢁ ꢂꢃ ꢄꢄ
ꢀꢁꢁ ꢈ ꢃꢄ ꢅ ꢆ ꢀꢁꢁ ꢈ ꢃꢄ ꢇ ꢆ ꢀ ꢁꢁ ꢈꢃ ꢄꢄ
SLUS499A – NOVEMBER 2001 – REVISED JANUARY 2002
APPLICATION INFORMATION
open lamp shutdown/no-lock operation (continued)
Figure 20 shows the startup performance of the UCC397x family based system with a broken or open lamp.
The open lamp trip level is typically set 20% to 50% higher than the required strike voltage of the lamp, in this
example the open lamp trip level is set at a low 500 V
. As seen in Figure 21, the lamp does not strike before
RMS
the OPEN/SD pin reaches 1.5 V indicating an open lamp, the controller retries seven times before entering an
error shutdown state (see the state diagram in the pin description section).
V
COMP
V
V
OPEN/SD
PZT
Figure 20. Start-Up With Open Lamp
A second type of failure mode occurs if the system fails to control lamp current. Assuming a proper feedback
network, this failure can occur if the input voltage is too low to operate the lamp or if one of the components in
the power path is open, shorted, or broken. These failures are detected at the COMP pin. Figure 21 shows the
system response where the input voltage is not sufficient for lamp operation. At startup the frequency sweeps
through the range until COMP reaches 2.5 V, the controller attempts seven retries before entering the error
shutdown state. Notice the slope on the COMP pin (trace 2) changes as the system attempts to operate the lamp
in a high gain region but is ultimately unsuccessful.
23
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