DS3991Z+PP Maxim Integrated Products, DS3991Z+PP Datasheet - Page 8

• Manufacturer Part Number: DS3991Z+PP
• Description: IC CTRLR CCFL PUSH-PULL 16-SOIC
• Manufacturer: Maxim Integrated Products
• Type: CCFL Controllerr

Specifications of DS3991Z+PP

• Frequency: 40 ~ 80 kHz
• Current - Supply: 5mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Details

Low-Cost CCFL Controller
The DS3991 is available for both push-pull and half-
bridge drive topologies. In both drive topologies, the
DS3991 drives two logic-level MOSFETs. The DS3991
alternately turns on the two MOSFETs to create the high-
voltage AC waveform on the secondary. By varying the
duration of the MOSFET turn-on times, the controller is
able to accurately control the amount of current flowing
through the CCFL lamp. See the Typical Push-Pull
Application and Typical Half-Bridge Application figures.
The DS3991 can also drive more than one CCFL lamp
per channel. The Typical Push-Pull Application, Multiple
Lamps Per Channel and Typical Half-Bridge Application,
Multiple Lamps Per Channel figures show an application
driving three lamps.
A series resistor on the low-voltage side of the CCFL
lamp enables current monitoring. The voltage developed
across this resistor is fed to the lamp current monitor
(LCM) input on the DS3991. The DS3991 compares the
resistor voltage against an internal reference voltage to
determine the duty cycle for the MOSFET gates. See the
Main System Block Diagram and the CCFL Channel
Block Diagram for more information.
8
_______________________________________________________________________________________
LAMP FREQUENCY
CHANNEL ENABLE
BURST-DIMMING
(40kHz TO 80kHz)
CHANNEL FAULT
PWM SIGNAL
Detailed Description
CONTROLLER
DIGITAL
CCFL
LAMP MAXIMUM VOLTAGE REGULATION
64 LAMP CYCLE
INTEGRATOR
LAMP STRIKE AND REGULATION
LAMP OVERCURRENT
OVERVOLTAGE
LAMP OUT
The DS3991 uses burst dimming to control the lamp
brightness. During the high period of the DPWM cycle,
the lamp is driven at the selected lamp frequency
(40kHz to 80kHz) as shown in Figure 1. This part of the
cycle is also called the burst period because of the
lamp-frequency burst that occurs during this time.
During the low period of the DPWM cycle, the controller
disables the MOSFET gate drivers so the lamp is not
driven. This causes the current to stop flowing in the
lamp, but the time is short enough to keep the lamp
from de-ionizing. Dimming is increased/decreased by
adjusting (i.e., modulating) the burst-period duty cycle.
At the beginning of each burst-dimming cycle, soft-start
slowly ramps the lamp current to reduce the potential to
create audible transformer noise.
There are two methods to control the duty cycle and
frequency of the burst-dimming DPWM. If the PWM_EN
pin is tied low, then the analog-control method is
enabled; a 0V to 3.3V analog voltage at the BRIGHT
input pin determines the duty cycle of a digital pulse-
width modulated (DPWM) signal. The frequency of the
DPWM signal is determined by the value of the resistor
tied from the POSC pin to ground. The slope of the
BRIGHT dimming input is either positive or negative
based on whether the SLOPE pin is tied low or high,
respectively.
CCFL Channel Block Diagram
DRIVERS
GATE
400mV
2.0V
1.0V
1.0V
LCM
LAMP CURRENT MONITOR
OVD
OVERVOLTAGE DETECTOR
GA
GB
Dimming Control
MOSFET
GATE DRIVERS
DS3991