DS3991Z+T&R/PPV Maxim Integrated Products, DS3991Z+T&R/PPV Datasheet - Page 10

• Manufacturer Part Number: DS3991Z+T&R/PPV
• Description: Display Drivers Low-Cost CCFL Contro ller All N-FET Drive
• Manufacturer: Maxim Integrated Products

Specifications of DS3991Z+T&R/PPV

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Low-Cost CCFL Controller
Figure 2. Setting the SVML and SVMH Threshold Voltages
Figure 3. Fault-Handling Flowchart
causing spurious operation when V
point. This monitor cannot be disabled by any means.
The DS3991 provides extensive fault monitoring. It can
detect open-lamp, lamp overcurrent, failure to strike,
and overvoltage conditions. Figure 3 shows a flowchart
of how the DS3991 controls and monitors each lamp.
The steps are as follows:
10
______________________________________________________________________________________
LAMP OVERCURRENT
(INSTANTANEOUS)
V
TRIP
R
R
2
1
V
INV
Fault Monitoring
(RAMP AND REGULATE TO
CURRENT BOUNDED BY
CC
IF LAMP REGULATION
INVERTER SUPPLIES
AT PROPER LEVELS?
THRESHOLD IS MET
OVD THRESHOLD)
SVML
(REGULATE LAMP
LAMP VOLTAGE)
2.0V
STRIKE LAMP
DEVICE AND
RUN LAMP
is near the trip
YES
MOSFET GATE DRIVERS ENABLED
DS3991
The lamps do not turn on unless the DS3991 supply
voltage is > 4.5V and the voltage at the supply-voltage
monitor low (SVML) input is > 2V and the supply-volt-
age monitor high (SVMH) input is < 2V.
When both the DS3991 and the DC inverter supplies are
at acceptable levels, the DS3991 attempts to strike the
lamps. The DS3991 slowly ramps up the MOSFET gate
duty cycle until the lamp strikes. The controller detects
LAMP STRIKE TIMEOUT
(65,536 LAMP CYCLES)
(65,536 LAMP CYCLES)
LAMP-OUT TIMEOUT
(64 LAMP CYCLES)
OVERVOLTAGE
SVMH
2.0V
OR TAKE SVML BELOW 2V OR SVMH
(MUST POWER CYCLE THE DS3991
V
INV
THE CCFL CONTROLLER)
R
V
R
ABOVE 2V TO RESET
2
TRIP
1
FAULT STATE