參數(shù)資料
型號(hào)： DS3994
廠商： Maxim Integrated Products, Inc.
英文描述： 4-Channel Cold-Cathode Fluorescent Lamp Controller
中文描述： 4通道冷陰極熒光燈控制器
文件頁(yè)數(shù)： 17/28頁(yè)
文件大小： 557K
代理商： DS3994
D
4-Channel Cold-Cathode
Fluorescent Lamp Controller
____________________________________________________________________
17
Figure 9 shows a flowchart of how the DS3994 controls
and monitors each lamp. The steps are as follows:
1) Supply Check
—
The lamps will not turn on unless the
DS3994 supply voltage is
≥
4.5V and the voltage at
the supply voltage monitor (SVM) input is
≥
2V.
2) Strike Lamp
—
When both the DS3994 and the DC
inverter supplies are above these minimum values,
the DS3994 attempts to strike each enabled chan-
nel. The DS3994 slowly ramps up the MOSFET gate
duty cycle until the lamp strikes. The controller
detects that the lamp has struck by detecting cur-
rent flow in the lamp. If during the strike ramp the
maximum allowable voltage is reached, the con-
troller stops increasing the MOSFET gate duty cycle
to keep from overstressing the system. The DS3994
goes into a fault handling state (step 4) if the lamp
has not struck after the timeout period as defined by
the LST0 and LST1 control bits in the CR3 register. If
an overvoltage event is detected during the strike
attempt, the DS3994 disables the MOSFET gate dri-
vers and goes into the fault handling state.
3) Run Lamp
—
Once the lamp is struck, the DS3994
moves to the Run Lamp stage. In the Run Lamp
stage, the DS3994 adjusts the MOSFET gate duty
cycle to optimize the lamp current. The gate duty
cycle is always constrained to keep the system from
exceeding the maximum allowable lamp voltage.
If lamp current ever drops below the Lamp Out ref-
erence point for the period as defined by the LST0
and LST1 control bits in the CR3 register, then the
lamp is considered extinguished. In this case the
MOSFET gate drivers are disabled and the device
moves to the fault handling stage.
4) Fault Handling
—
During fault handling, the DS3994
performs an optional (user-selectable) automatic
retry to attempt to clear all faults except a lamp
overcurrent. The automatic retry makes 14 addition-
al attempts to rectify the fault before declaring the
channel in a Fault State and permanently disabling
the channel. Between each of the 14 attempts, the
controller waits 1024 lamp cycles. In the case of a
lamp overcurrent, the DS3994 instantaneously
declares the channel to be in a Fault State and per-
manently disables the channel. The DS3994 can be
configured to disable all channels if one or more
channels enters a Fault State or it can be configured
to disable only the channel where the fault occurred.
Once a Fault State is entered, the channel remains
in that state until one of the following occurs:
V
CC
drops below the UVLO threshold.
The SVM threshold is crossed.
The channel is disabled.
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