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Rev 0; 1/08
Low-Cost CCFL Controller
General Description
The DS3991 is a controller for cold-cathode fluorescent lamps (CCFLs) that are used to backlight liquid-crystal displays (LCDs). The DS3991 is available for both push-pull and half-bridge drive topologies. The DS3991 converts a DC voltage (5V to 24V) to the high-voltage (300VRMS to 1400VRMS) AC waveform that is required to power the CCFLs. The push-pull and halfbridge drive schemes use a minimal number of external components, which reduces component and assembly cost and makes the printed circuit board (PCB) design easy to implement. Both drive schemes provide an efficient DC to AC conversion and produce near-sinusoidal waveforms.
Features
CCFL Controller for Backlighting LCD Panels Minimal External Components Required Lamp Fault Monitoring for Lamp-Open, LampOvercurrent, Failure-to-Strike, and Overvoltage Conditions Accurate (5%) On-Board Oscillator for Lamp Frequency (40kHz to 80kHz) Accurate (5%) On-Board Oscillator for DPWM Burst-Dimming Frequency (80Hz to 300Hz) Device Supply Undervoltage Lockout Inverter Supply Undervoltage and Overvoltage Lockouts Soft-Start on Burst-Dimming Minimizes Audible Transformer Noise Strike Frequency Boost 100% to < 10% Dimming Range Low Cost Single-Supply Operation Range: 4.5V to 5.5V Temperature Range: -40C to +85C 16-Pin SO Package (150 mils)
DS3991
Applications
LCD PC Monitors LCD TVs
Ordering Information
PART DS3991V+C DS3991V+T&R/C DS3991V+ DS3991V+T&R CONFIGURATION Push-Pull Push-Pull Half-Bridge Half-Bridge TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C DIMMING FREQUENCY RANGE (Hz) 80 to 300 80 to 300 80 to 300 80 to 300 PIN-PACKAGE 16 SO (150 mils) 16 SO (150 mils) 16 SO (150 mils) 16 SO (150 mils)
+Denotes a lead-free package. T&R = Tape and reel.
TOP VIEW
SLOPE 1 VCC 2
Pin Configuration
16 SVML 15 SVMH 14 VCC 13 GND
Typical Operating Circuits appear at end of data sheet.
VCC 3 VCC 4 LOSC 5 POSC/PWM 6 BRIGHT 7 PWM_EN 8
DS3991
12 OVD 11 LCM 10 GB 9 GA
SO
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Cost CCFL Controller DS3991
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC Relative to Ground ..........-0.5V to +6.0V Voltage Range on Any Lead Other than VCC ..............................................-0.5V to (VCC + 0.5V), not to exceed +6.0V Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-55C to +125C Soldering Temperature...................See J-STD-020 Specification
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
(TA = -40C to +85C)
PARAMETER Supply Voltage Input Logic 1 Input Logic 0 BRIGHT, SVML, SVMH Voltage Range LCM and OVD Voltage Range Gate-Driver Output Charge Loading LOSC and POSC Loading SYMBOL VCC VIH VIL VRA VRC QG COSC (Note 2) (Note 1) CONDITIONS MIN 4.5 2.2 -0.3 -0.3 -0.3 TYP MAX 5.5 VCC + 0.3 +0.8 VCC+ 0.3 VCC + 0.3 20 20 UNITS V V V V V nC pF
ELECTRICAL CHARACTERISTICS
(VCC = +4.5V to 5.5V, TA = -40C to +85C.)
PARAMETER Supply Current Low-Level Output Voltage (GA, GB) High-Level Output Voltage (GA, GB) UVLO Threshold: VCC Rising UVLO Threshold: VCC Falling UVLO Hysteresis SVML Falling Threshold SVMH Rising Threshold SVML and SVMH Hysteresis LCM and OVD DC Bias Voltage LCM and OVD Input Resistance Lamp-Off Threshold Lamp Overcurrent Threshold SYMBOL ICC VOL VOH VUVLOR VUVLOF VUVLOH VSVMLT VSVMHT VSVMH VDCB RDCB VLOT VLOCT (Note 3) (Note 3) 1.65 3.25 1.94 1.94 3.7 100 2.00 2.00 150 1.35 50 1.75 3.35 1.85 3.45 2.06 2.06 CONDITIONS GA, GB loaded with 300pF I OL = 4mA I OH = -1mA 2.4 4.3 MIN TYP 5 MAX 10 0.4 UNITS mA V V V V mV V V mV V k V V
2
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Low-Cost CCFL Controller
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.5V to 5.5V, TA = -40C to +85C.)
PARAMETER Lamp Regulation Threshold OVD Threshold Lamp Frequency Lamp Frequency Tolerance Burst-Dimming PWM Frequency Burst-Dimming PWM Frequency Tolerance BRIGHT Voltage: Minimum Brightness BRIGHT Voltage: Maximum Brightness Gate-Driver Output Rise/Fall SYMBOL VLRT VOVDT LFOSCI LFTOL PFOSCI PFTOL VBMIN VBMAX tR/tF POSC resistor 0.1% over temperature SLOPE = 0 SLOPE = 1 SLOPE = 0 SLOPE = 1 CL = 600pF 3.3 3.3 0 100 LOSC resistor 0.1% over temperature; measured from 0C to +85C (Note 3) (Note 3) CONDITIONS MIN 2.29 2.25 40 -5 80 -5 TYP 2.35 2.35 MAX 2.41 2.45 80 +5 300 +5 0 UNITS V V kHz % Hz % V V V V ns
DS3991
Note 1: All voltages are referenced to ground unless otherwise noted. Currents into the IC are positive; currents out of the IC are negative. Note 2: During fault conditions, if AC-coupled, LCM and OVD can go below ground by up to 1V for up to 1s. Note 3: Threshold voltage includes the DC bias-voltage offset.
Typical Operating Characteristics
(VCC = 5.0V, TA = +25C, unless otherwise noted.)
ACTIVE SUPPLY CURRENT vs. SUPPLY VOLTAGE
DS3991 toc01
ACTIVE SUPPLY CURRENT vs. TEMPERATURE
DS3991 toc02
INTERNAL FREQUENCY CHANGE vs. TEMPERATURE
0.8 FREQUENCY CHANGE (%) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -40.0 22.5 TEMPERATURE (C) 85.0 LAMP FREQUENCY DPWM FREQUENCY
DS3991 toc03
6.0 5.5 SUPPLY CURRENT (mA) 5.0 4.5 4.0 DPWM = 10% 3.5 SVM TRIPPED 3.0 4.5 4.7 4.9 GATE QC = 4.5nC fLOSC = 49.6kHz 5.1 5.3 DPWM = 100% DPWM = 50%
6.0
1.0
SUPPLY CURRENT (mA)
5.5 VCC = 5.5V 5.0 VCC = 5.0V 4.5 VCC = 4.5V GATE QC = 4.5nC fLOSC = 49.6kHz DPWM = 100% 22.5 TEMPERATURE (C) 85.0
4.0 5.5 -40.0
SUPPLY VOLTAGE (V)
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Low-Cost CCFL Controller DS3991
Typical Operating Characteristics (continued)
(VCC = 5.0V, TA = +25C, multilamp configuration, unless otherwise noted.)
PUSH-PULL TYPICAL OPERATION AT VINV = 12.5V
20s 5.0V 20s 5.0V 20s 2.0V 20s 2.0V
PUSH-PULL TYPICAL STARTUP WITH SVM
DS3991 toc05
DS3991 toc04
GA
50ms 2.0V 50ms 5.0V 50ms 2.0V 50ms 2.0V
SVM
GB
GB
LCM
LCM
OVD
OVD
PUSH-PULL SOFT-START AT VINV = 12.5V
0.1ms 5.0V 0.1ms 5.0V 0.1ms 2.0V 0.1ms 2.0V
PUSH-PULL LAMP STRIKE, EXPANDED VIEW
DS3991 toc06 DS3991 toc07
GA
50ms 5.0V 50ms 5.0V 50ms 2.0V 50ms 2.0V
GA
GB
GB
LCM
LCM
OVD
OVD
PUSH-PULL BURST DIMMING AT 133Hz, 10%
DS3991 toc08
PUSH-PULL BURST DIMMING AT 133Hz, 50%
DS3991 toc09
1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V
GA
1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V
GA
GB
GB
LCM
LCM
OVD
OVD
4
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Low-Cost CCFL Controller
Typical Operating Characteristics (continued)
(VCC = 5.0V, TA = +25C, single-lamp configuration, unless otherwise noted.)
DS3991
HALF-BRIDGE NORMAL OPERATION, 20s
DS3991 toc10
HALF-BRIDGE SOFT-START AT VINV = 12.5V
50s 5.0V 50s 5.0V 50s 2.0V 50s 2.0V
DS3991 toc11
20s 5.0V 20s 5.0V 20s 2.0V 20s 2.0V
GA
GA
GB
GB
LCM
LCM
OVD
OVD
HALF-BRIDGE LAMP STRIKE, EXPANDED VIEW
DS3991 toc12
HALF-BRIDGE BURST DIMMING AT 166Hz, 10%
DS3991 toc13
0.5ms 5.0V 0.5ms 5.0V 0.5ms 2.0V 0.5ms 2.0V
GA
1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V
GA
GB
GB
LCM
LCM
OVD
OVD
HALF-BRIDGE BURST DIMMING AT 166Hz, 50%
DS3991 toc14
1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V
GA
GB
LCM
OVD
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Low-Cost CCFL Controller DS3991
Pin Description
PIN NAME I/O FUNCTION BRIGHT Slope Select. This digital input determines the slope of the BRIGHT input when an analog DC voltage is used to control lamp brightness (PWM_EN = 0). SLOPE = 0: positive slope (0V = minimum brightness, 3.3V = 100% brightness) SLOPE = 1: negative slope (0V = 100% brightness, 3.3V = minimum brightness) Connect to Voltage Supply. These pins should be connected to the voltage supply pin, VCC. O Lamp Oscillator Resistor Adjust. A resistor (RLOSC) to ground on this pin sets the frequency of the lamp oscillator (FLOSC). (RLOSC x FLOSC = 4.0E9). Burst-Dimming PWM Oscillator Resistor Adjust/PWM Digital Input. If PWM_EN = 0, a resistor (RPOSC) to ground on this pin sets the frequency (FPOSC) of the burst-dimming PWM oscillator (RPOSC x F POSC = 4.0E6). If PWM_EN =1, a digital 80Hz to 300Hz PWM signal at this input controls the lamp brightness. Lamp-Brightness Control. If PWM_EN = 0, a 0V to 3.3V analog DC voltage at this input controls the brightness of the lamp. PWM Lamp-Brightness Control Enable. This digital input determines whether the BRIGHT or POSC/PWM input is used to control lamp brightness. PWM_EN = 0 = PWM disabled (analog DC voltage applied at the BRIGHT input) PWM_EN = 1 = PWM enabled (digital PWM signal applied at the POSC/PWM input) MOSFET Gate Drive A. Drives a logic-level power MOSFET. MOSFET Gate Drive B. Drives a logic-level power MOSFET. Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with the low-voltage side of the lamp. Overvoltage Detection Input. Lamp voltage is monitored by a capacitor divider placed on the high-voltage side of the lamp. Signal Ground Voltage Supply, 4.5V to 5.5V Supply Voltage Monitor High. The DC inverter-supply voltage is monitored by an external resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the maximum allowable range of the DC inverter supply. Pulling this input above 2V turns the lamps off and resets the controller. Connect to GND if not used. Supply Voltage Monitor Low. The DC inverter-supply voltage is monitored by an external resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the minimum allowable range of the DC inverter supply. Pulling this input below 2V turns the lamps off and resets the controller. Connect to VCC if not used.
1
SLOPE
I
2, 3, 4 5
VCC LOSC
6
POSC/ PWM
O/I
7
BRIGHT
I
8
PWM_EN
I
9 10 11 12 13 14
GA GB LCM OVD GND VCC
O O I I
15
SVMH
I
16
SVML
I
6
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Low-Cost CCFL Controller
Main System Block Diagram
DS3991
UVLO SYSTEM ENABLE/ POR 2.0V VREF
VCC (4.5V TO 5.5V)
DS3991
2.0V
SVML SUPPLY VOLTAGE MONITOR LOW SVMH SUPPLY VOLTAGE MONITOR HIGH
FAULT HANDLING LOSC EXTERNAL RESISTOR LAMP FREQUENCY SET 40kHz TO 80kHz OSCILLATOR (5%)
CHANNEL FAULT CHANNEL ENABLE LCM LAMP CURRENT MONITOR CCFL CONTROLLER
PWM_EN ANALOG LAMP BRIGHTNESS CONTROL (PWM_EN = 0)
(SEE THE CCFL CHANNEL BLOCK DIAGRAM) POSITIVE OR NEGATIVE SLOPE SELECT 80Hz TO 300Hz OSCILLATOR (5%) RAMP GENERATOR MUX
OVD OVERVOLTAGE DETECTION
BRIGHT SLOPE
GA MOSFET GB GATE DRIVERS DPWM SIGNAL GND
PWM LAMP BRIGHTNESS CONTROL (PWM_EN = 1) EXTERNAL RESISTOR BURST-DIMMING FREQUENCY SET
POSC
80Hz TO 300Hz
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Low-Cost CCFL Controller DS3991
CCFL Channel Block Diagram
LAMP OUT CHANNEL ENABLE CHANNEL FAULT LAMP OVERCURRENT 2.0V BURST-DIMMING PWM SIGNAL DIGITAL CCFL CONTROLLER LAMP STRIKE AND REGULATION 64 LAMP CYCLE INTEGRATOR OVERVOLTAGE 1.0V 400mV
DS3991
LCM LAMP CURRENT MONITOR
OVD OVERVOLTAGE DETECTOR 1.0V GA GB
LAMP MAXIMUM VOLTAGE REGULATION LAMP FREQUENCY (40kHz TO 80kHz)
GATE DRIVERS
MOSFET GATE DRIVERS
Detailed Description
The DS3991 is available for both push-pull and halfbridge drive topologies. In both drive topologies, the DS3991 drives two logic-level MOSFETs. The DS3991 alternately turns on the two MOSFETs to create the highvoltage 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 Lamp Per Channel and Typical Half-Bridge Application, Multiple Lamp 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.
Dimming Control
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 pulsewidth 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.
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Low-Cost CCFL Controller DS3991
BURST-DIMMING PWM SIGNAL (EITHER CREATED INSIDE THE DS3991 OR SOURCED AT THE POSC/PWM PIN) 80Hz TO 300Hz
LAMP CURRENT
SOFT-START
Figure 1. Digital PWM Dimming and Soft-Start
If the PWM_EN pin is tied high, the digital control method is enabled and an external PWM signal between 80Hz and 300Hz is applied at the POSC/PWM pin to set the brightness of the lamp. In the digital control method, the SLOPE and BRIGHT pins are not used.
Supply Monitoring
The DS3991 has supply-voltage monitors (SVML and SVMH) for the inverter's DC supply (V INV ) and an undervoltage lockout for the VCC supply to ensure that voltage levels are adequate for proper operation. The inverter supply is monitored for overvoltage conditions at the SVMH pin and undervoltage conditions at the SVML pin. External resistor-dividers at each SVM input feed into two comparators, both having 2V thresholds (see Figure 2). Using the equation below to determine the resistor values, the SVMH and SVML trip points (VTRIP) can be customized to shut off the inverter when the inverter supply voltage rises above or drops below specified values. Operating with the inverter supply at too low of a level can prevent the transformer from reaching the strike voltage and could potentially cause numerous other problems. Operating with the inverter voltage at too high of a level can be damaging to the inverter components. Proper use of the SVMs can prevent these problems. If desired, the high and/or low SVMs can be disabled by connecting the SVMH pin to GND and the SVML pin to VCC.
VTRIP = 2.0 R1 + R 2 R1
Lamp Strike
On lamp strike, the DS3991 boosts the normal operating lamp frequency by 33%. This is done to increase the voltage created and help ensure that the lamp strikes. Once the controller detects that the lamp has struck, the frequency is returned to the normal lamp frequency.
Setting the Lamp and DPWM Frequencies Using External Resistors Both the lamp and DPWM frequencies are set using external resistors. The resistance required for either frequency can be determined using the following formula:
ROSC = K fOSC
where K = 4000k x kHz for lamp frequency calculations, K = 4k x kHz for DPWM frequency calculations. Example: Select the resistor values to configure the DS3991 to have a 50kHz lamp frequency and a 160Hz DPWM frequency. For the DPWM resistor calculation, K = 4 k x kHz. For the lamp frequency resistor (RLOSC) calculation, K = 4000 k x kHz. The formula above can now be used to calculate the resistor values for RLOSC and RPOSC as follows:
RLOSC = 4000k kHz = 80k 50kHz 4k kHz = 25k 0.160kHz
RPOSC =
The SVMH and SVML are high-impedance inputs and noise on the inverter supply can cause the monitors to inadvertently trigger even though the inputs contain hysteresis. The user may wish to add a lowpass filter to reduce the noise present at the SVMH and SVML inputs. The VCC monitor is a 5V supply undervoltage lockout (UVLO) that prevents operation when the DS3991 does not have adequate voltage for its analog circuitry to operate or to drive the external MOSFETs. The VCC monitor features hysteresis to prevent VCC noise from
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Low-Cost CCFL Controller DS3991
VINV R2 VTRIP R1 2.0V 2.0V SVML VINV R2
DS3991
SVMH
VTRIP R1
Figure 2. Setting the SVML and SVMH Threshold Voltages
DEVICE AND INVERTER SUPPLIES AT PROPER LEVELS? YES
FAULT STATE (MUST POWER CYCLE THE DS3991 OR TAKE SVML BELOW 2V OR SVMH ABOVE 2V TO RESET THE CCFL CONTROLLER)
STRIKE LAMP (RAMP AND REGULATE TO OVD THRESHOLD)
LAMP STRIKE TIMEOUT (65,536 LAMP CYCLES)
IF LAMP REGULATION THRESHOLD IS MET
OVERVOLTAGE (64 LAMP CYCLES)
LAMP OVERCURRENT (INSTANTANEOUS)
RUN LAMP (REGULATE LAMP CURRENT BOUNDED BY LAMP VOLTAGE)
LAMP-OUT TIMEOUT (65,536 LAMP CYCLES)
MOSFET GATE DRIVERS ENABLED
Figure 3. Fault-Handling Flowchart
causing spurious operation when VCC is near the trip point. This monitor cannot be disabled by any means.
Fault Monitoring
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
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-voltage 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
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Low-Cost CCFL Controller
that the lamp has struck by detecting current flow in the lamp. If during the strike ramp, the maximum allowable voltage is reached, the controller stops increasing the MOSFET gate duty cycle to keep from overstressing the system. The DS3991 goes into a fault-handling state if the lamp has not struck after 65,536 lamp cycles. If an overvoltage event is detected during the strike attempt, the DS3991 disables the MOSFET gate drivers and goes into the fault handling state. Once the lamp is struck, the DS3991 moves to the runlamp stage. In the run-lamp stage, the DS3991 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 reference point for 65,536 lamp cycles, the lamp is considered extinguished. In this case the MOSFET gate drivers are disabled and the device moves to the fault-handling stage. In the case of a lamp overcurrent, the DS3991 instantaneously declares the controller to be in a fault state. If the DS3991 goes into the fault state, the DS3991 shuts down. Once a fault state is entered, the controller remains in that state until one of the following occurs:
Applications Information
Component Selection
External component selection has a large impact on the overall system performance and cost. The two most important external components are the transformers and MOSFETs. The transformer should be able to operate in the 40kHz to 80kHz frequency range of the DS3991, and the turns ratio should be selected so the MOSFET drivers run at 28% to 35% duty cycle during steady-state operation. The transformer must be able to withstand the high open-circuit voltage that is used to strike the lamp. Additionally, its primary/secondary resistance and inductance characteristics must be considered because they contribute significantly to determining the efficiency and transient response of the system. Table 1 shows a transformer specification that has been utilized for a 12V inverter supply, 438mm x 2.2mm lamp design. The MOSFETs must have a threshold voltage that is low enough to work with logic-level signals, a low on-resistance to maximize efficiency and limit the MOSFET's power dissipation, and a breakdown voltage high enough to handle the transient. For push-pull topologies, the breakdown voltage of the MOSFETs should be a minimum of 3x the inverter voltage supply. Additionally, the total gate charge must be less than QG, which is specified in the Recommended Operating Conditions table.
DS3991
* VCC drops below the UVLO threshold * SVML input drops below 2.0V * SVMH input goes above 2.0V
Table 1. Transformer Specifications (as used in the Typical Operating Circuits)
PARAMETER Turns Ratio (Secondary/Primary) Push-Pull Type Frequency Output Power Output Current Primary DCR Secondary DCR Primary Leakage Secondary Leakage Primary Inductance Secondary Inductance Secondary Output Voltage 1000ms (min) Continuous 2000 1000 Center tap to one end 5 200 500 12 185 70 500 H mH H mH VRMS CONDITIONS (Notes 1, 2, 3) 40 MIN TYP 40 80 80 6 8 kHz W mA m MAX UNITS
Turns Ratio (Secondary/Primary) Half-Bridge Type (Note 3)
Note 1: Primary should be bifilar wound with center-tap connection. Note 2: Turns ratio is defined as secondary winding divided by the sum of both primary windings. Note 3: This is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to Application Note 3375 for more information on push-pull type applications. ______________________________________________________________________________________ 11
Low-Cost CCFL Controller DS3991
Typical Operating Circuits
Typical Push-Pull Application
ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V 10%) INVERTER SUPPLY VOLTAGE (5V 10% TO 24V 10%) VCC VCC VCC VCC SVMH SVML
DS3991
ANALOG LAMP BRIGHTNESS CONTROL BRIGHT DUAL POWER MOSFET PWM_EN SLOPE GA LOSC RESISTOR SET LAMP FREQUENCY TRANSFORMER GB OVERVOLTAGE DETECTION LAMP CURRENT MONITOR CCFL LAMP
PWM LAMP BRIGHTNESS CONTROL (OPTIONAL) RESISTOR SET BURST-DIMMING FREQUENCY
POSC/PWM
OVD LCM GND
12
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Low-Cost CCFL Controller
Typical Operating Circuits (continued)
Typical Half-Bridge Application
DS3991
ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V 10%) INVERTER SUPPLY VOLTAGE (5V 10% TO 24V 10%) VCC VCC VCC VCC SVMH SVML
DS3991
ANALOG LAMP BRIGHTNESS CONTROL BRIGHT PWM_EN SLOPE
GA CCFL LAMP
LOSC RESISTOR SET LAMP FREQUENCY TRANSFORMER GB DUAL POWER MOSFET POSC/PWM OVD LCM GND OVERVOLTAGE DETECTION LAMP CURRENT MONITOR
PWM LAMP BRIGHTNESS CONTROL (OPTIONAL) RESISTOR SET BURST-DIMMING FREQUENCY
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13
Low-Cost CCFL Controller DS3991
Typical Operating Circuits (continued)
Typical Push-Pull Application, Multiple Lamps Per Channel
ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V 10%)
INVERTER SUPPLY VOLTAGE (5V 10% TO 24V 10%)
VCC VCC VCC VCC
SVML
SVMH
DUAL POWER MOSFET
DS3991
GA ANALOG LAMP BRIGHTNESS CONTROL BRIGHT CCFL LAMP A
GB
+5V PWM_EN SLOPE LCM 2N3904
CCFL LAMP B
+5V LOSC RESISTOR SET LAMP FREQUENCY 2N3904
CCFL LAMP C
+5V POSC/PWM RESISTOR SET BURST-DIMMING FREQUENCY
2N3904
GND
OVD
14
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Low-Cost CCFL Controller
Typical Operating Circuits (continued)
Typical Half-Bridge Application, Multiple Lamps Per Channel
ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V 10%)
DS3991
INVERTER SUPPLY VOLTAGE (5V 10% TO 24V 10%)
VCC VCC VCC VCC
SVML
SVMH
DS3991
GA ANALOG LAMP BRIGHTNESS CONTROL BRIGHT CCFL LAMP A
GB DUAL POWER MOSFET +5V PWM_EN SLOPE LCM 2N3904
CCFL LAMP B
+5V LOSC RESISTOR SET LAMP FREQUENCY 2N3904
CCFL LAMP C
+5V POSC/PWM RESISTOR SET BURST-DIMMING FREQUENCY
2N3904
GND
OVD
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15
Low-Cost CCFL Controller DS3991
Power-Supply Decoupling
To achieve best results, it is highly recommended that a decoupling capacitor be used on pin 14, the IC power-supply pin. Typical values of decoupling capacitors are 0.01F or 0.1F. Use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the VCC and GND pins of the IC to minimize lead inductance. Pins 2, 3, and 4 require connection to supply voltage (VCC) but do not require any additional decoupling.
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.
PACKAGE TYPE 16 SO (150 mils) DOCUMENT NO. 56-G2008-001
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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