Datasheet

DS3881
Single-Channel Automotive CCFL Controller
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Detailed Description
The DS3881 uses a push-pull drive scheme to convert
a DC voltage (8V to 16V) to the high-voltage (300V
RMS
to 1000V
RMS
) AC waveform that is required to power
the CCFL. The push-pull drive scheme uses a minimal
number of external components, which reduces assem-
bly cost and makes the printed circuit board design
easy to implement. The push-pull drive scheme also
provides an efficient DC-to-AC conversion and pro-
duces near-sinusoidal waveforms.
Each DS3881 drives two logic-level n-channel
MOSFETs that are connected between the ends of a
step-up transformer and ground (see the Typical
Operating Circuit ). The transformer has a center tap on
the primary side that is connected to a DC voltage sup-
ply. The DS3881 alternately turns on the two MOSFETs
to create the high-voltage AC waveform on the sec-
ondary side. By varying the duration of the MOSFET
turn-on times, the CCFL current is able to be accurately
controlled.
A resistor in series with the CCFL’s ground connection
enables current monitoring. The voltage across this
resistor is fed to the lamp current monitor (LCM) input
and compared to an internal reference voltage to deter-
mine the duty cycle for the MOSFET gates. The CCFL
receives current monitoring and control, which maxi-
mizes the lamp’s brightness and lifetime.
Block diagrams of the DS3881 are shown in Figures 1
and 2. More operating details of the DS3881 are dis-
cussed on the following pages of this data sheet.
Memory Registers and
I
2
C-Compatible Serial Interface
The DS3881 uses an I
2
C-compatible serial interface for
communication with the on-board EEPROM and SRAM
configuration/status registers as well as user memory.
The configuration registers, which are a mixture of
shadowed EEPROM and SRAM, allow the user to cus-
tomize many DS3881 parameters such as the soft-start
ramp rate, the lamp and dimming frequency sources,
brightness of the lamps, fault-monitoring options, chan-
nel enabling/disabling, EMI control, and lamp current
overdrive control. The eight bytes of NV user memory
can be used to store manufacturing data such as date
codes, serial numbers, or product identification num-
bers. The device is shipped from the factory with the
configuration registers programmed to a set of default
configuration parameters. To inquire about custom pro-
gramming, contact the factory.
GATE
DRIVERS
MOSFET
GATE
DRIVERS
GA1
GB1
DIGITAL
CCFL
CONTROLLER
CHANNEL FAULT
512 x LAMP FREQUENCY
[20.48MHz ~ 51.20MHz]
LAMP FREQUENCY
[40kHz ~ 80kHz]
DIMMING PWM SIGNAL
CHANNEL ENABLE
V
LRT
(1.0V NOMINAL)
LCM1
LAMP CURRENT
MONITOR
300mV
2.5V
LAMP OVERCURRENT
LAMP STRIKE AND REGULATION
LOCE BIT IN CR1.0
LAMP OUT
1.0V
OVD1
OVERVOLTAGE DETECTOR
LAMP MAXIMUM VOLTAGE REGULATION
64 LAMP CYCLE
INTEGRATOR
OVERVOLTAGE
Figure 2. Per Channel Logic Diagram
Functional Diagrams (continued)