Rev 0; 1/08 Low-Cost CCFL Controller 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. Applications LCD PC Monitors LCD TVs 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: -40°C to +85°C ♦ 16-Pin SO Package (150 mils) Ordering Information PART DS3991V+C DS3991V+T&R/C CONFIGURATION TEMP RANGE DIMMING FREQUENCY RANGE (Hz) PIN-PACKAGE Push-Pull -40°C to +85°C 80 to 300 16 SO (150 mils) Push-Pull -40°C to +85°C 80 to 300 16 SO (150 mils) DS3991V+ Half-Bridge -40°C to +85°C 80 to 300 16 SO (150 mils) DS3991V+T&R Half-Bridge -40°C to +85°C 80 to 300 16 SO (150 mils) +Denotes a lead-free package. T&R = Tape and reel. Pin Configuration TOP VIEW Typical Operating Circuits appear at end of data sheet. SLOPE 1 16 SVML VCC 2 15 SVMH VCC 3 14 VCC VCC 4 LOSC 5 13 GND DS3991 12 OVD 11 LCM POSC/PWM 6 BRIGHT 7 10 GB PWM_EN 8 9 GA SO ________________________________________________________________ Maxim Integrated Products 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. 1 DS3991 General Description DS3991 Low-Cost CCFL Controller ABSOLUTE MAXIMUM RATINGS Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +125°C Soldering Temperature...................See J-STD-020 Specification 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 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 = -40°C to +85°C) PARAMETER Supply Voltage SYMBOL VCC CONDITIONS (Note 1) MIN TYP MAX UNITS 4.5 5.5 V V Input Logic 1 VIH 2.2 VCC + 0.3 Input Logic 0 VIL -0.3 +0.8 V BRIGHT, SVML, SVMH Voltage Range VRA -0.3 VCC+ 0.3 V LCM and OVD Voltage Range VRC -0.3 VCC + 0.3 V Gate-Driver Output Charge Loading QG 20 nC LOSC and POSC Loading COSC 20 pF TYP MAX UNITS 5 10 mA 0.4 V (Note 2) ELECTRICAL CHARACTERISTICS (VCC = +4.5V to 5.5V, TA = -40°C to +85°C.) PARAMETER SYMBOL CONDITIONS Supply Current ICC GA, GB loaded with 300pF Low-Level Output Voltage (GA, GB) VOL I OL = 4mA High-Level Output Voltage (GA, GB) VOH I OH = -1mA MIN 2.4 V UVLO Threshold: VCC Rising VUVLOR UVLO Threshold: VCC Falling VUVLOF 4.3 UVLO Hysteresis VUVLOH SVML Falling Threshold VSVMLT 1.94 2.00 2.06 V SVMH Rising Threshold VSVMHT 1.94 2.00 2.06 V SVML and SVMH Hysteresis 3.7 V V 100 mV VSVMH 150 LCM and OVD DC Bias Voltage VDCB 1.35 V LCM and OVD Input Resistance RDCB 50 k Lamp-Off Threshold Lamp Overcurrent Threshold 2 mV VLOT (Note 3) 1.65 1.75 1.85 V VLOCT (Note 3) 3.25 3.35 3.45 V _______________________________________________________________________________________ Low-Cost CCFL Controller (VCC = +4.5V to 5.5V, TA = -40°C to +85°C.) PARAMETER SYMBOL MIN TYP MAX UNITS VLRT (Note 3) 2.29 2.35 2.41 V OVD Threshold VOVDT (Note 3) 2.25 2.35 Lamp Frequency LFOSCI Lamp Frequency Tolerance LFTOL Burst-Dimming PWM Frequency PFOSCI Burst-Dimming PWM Frequency Tolerance PFTOL BRIGHT Voltage: Minimum Brightness VBMIN BRIGHT Voltage: Maximum Brightness VBMAX Gate-Driver Output Rise/Fall tR/tF Lamp Regulation Threshold CONDITIONS LOSC resistor ±0.1% over temperature; measured from 0°C to +85°C POSC resistor ±0.1% over temperature 2.45 V 40 80 kHz -5 +5 % 80 300 Hz -5 +5 % SLOPE = 0 0 SLOPE = 1 3.3 SLOPE = 0 3.3 V V V SLOPE = 1 0 V CL = 600pF 100 ns 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 = +25°C, unless otherwise noted.) 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 SUPPLY VOLTAGE (V) 5.5 VCC = 5.5V 5.0 VCC = 5.0V 4.5 5.3 VCC = 4.5V GATE QC = 4.5nC fLOSC = 49.6kHz DPWM = 100% 0.6 DPWM FREQUENCY 0.4 0.2 0 -0.2 LAMP FREQUENCY -0.4 -0.6 -0.8 -1.0 4.0 5.5 0.8 FREQUENCY CHANGE (%) DPWM = 50% 5.0 1.0 DS3991 toc02 DPWM = 100% SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 5.5 6.0 DS3991 toc01 6.0 INTERNAL FREQUENCY CHANGE vs. TEMPERATURE ACTIVE SUPPLY CURRENT vs. TEMPERATURE DS3991 toc03 ACTIVE SUPPLY CURRENT vs. SUPPLY VOLTAGE -40.0 22.5 TEMPERATURE (°C) 85.0 -40.0 22.5 85.0 TEMPERATURE (°C) _______________________________________________________________________________________ 3 DS3991 ELECTRICAL CHARACTERISTICS (continued) DS3991 Low-Cost CCFL Controller Typical Operating Characteristics (continued) (VCC = 5.0V, TA = +25°C, multilamp configuration, unless otherwise noted.) PUSH-PULL TYPICAL STARTUP WITH SVM PUSH-PULL TYPICAL OPERATION AT VINV = 12.5V DS3991 toc05 DS3991 toc04 20μs 5.0V 20μs 5.0V 20μs 2.0V 20μs 2.0V 50ms 2.0V GA 50ms 5.0V GB 50ms 2.0V LCM 50ms 2.0V 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 SVM GB LCM OVD PUSH-PULL LAMP STRIKE, EXPANDED VIEW DS3991 toc07 DS3991 toc06 50ms 5.0V GA 50ms 5.0V GB 50ms 2.0V LCM 50ms 2.0V OVD GA GB LCM OVD PUSH-PULL BURST DIMMING AT 133Hz, 50% PUSH-PULL BURST DIMMING AT 133Hz, 10% DS3991 toc09 DS3991 toc08 1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V 4 GA GB LCM OVD 1ms 5.0V 1ms 5.0V 1ms 2.0V 1ms 2.0V GA GB LCM OVD _______________________________________________________________________________________ Low-Cost CCFL Controller HALF-BRIDGE SOFT-START AT VINV = 12.5V HALF-BRIDGE NORMAL OPERATION, 20μs DS3991 toc11 DS3991 toc10 20μs 5.0V 20μs 5.0V 20μs 2.0V 20μs 2.0V 50μs 5.0V GA 50μs 5.0V GB 50μs 2.0V LCM 50μs 2.0V OVD GA GB LCM OVD HALF-BRIDGE BURST DIMMING AT 166Hz, 10% HALF-BRIDGE LAMP STRIKE, EXPANDED VIEW DS3991 toc13 DS3991 toc12 0.5ms 5.0V 0.5ms 5.0V 0.5ms 2.0V 0.5ms 2.0V 1ms 5.0V GA 1ms 5.0V GB 1ms 2.0V LCM 1ms 2.0V OVD GA GB LCM 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 _______________________________________________________________________________________ 5 DS3991 Typical Operating Characteristics (continued) (VCC = 5.0V, TA = +25°C, single-lamp configuration, unless otherwise noted.) Low-Cost CCFL Controller DS3991 Pin Description PIN 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) 1 SLOPE I 2, 3, 4 VCC Connect to Voltage Supply. These pins should be connected to the voltage supply pin, VCC. 5 LOSC 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). 6 POSC/ PWM O/I 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. 7 BRIGHT I Lamp-Brightness Control. If PWM_EN = 0, a 0V to 3.3V analog DC voltage at this input controls the brightness of the lamp. 8 PWM_EN I 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) 9 GA O MOSFET Gate Drive A. Drives a logic-level power MOSFET. 10 GB O MOSFET Gate Drive B. Drives a logic-level power MOSFET. 11 LCM I Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with the low-voltage side of the lamp. 12 OVD I Overvoltage Detection Input. Lamp voltage is monitored by a capacitor divider placed on the high-voltage side of the lamp. 13 GND Signal Ground 14 VCC Voltage Supply, 4.5V to 5.5V 15 16 6 NAME SVMH SVML I 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. I 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. _______________________________________________________________________________________ Low-Cost CCFL Controller UVLO SYSTEM ENABLE/ POR 2.0V DS3991 VCC (4.5V TO 5.5V) VREF SVML SUPPLY VOLTAGE MONITOR LOW 2.0V SVMH SUPPLY VOLTAGE MONITOR HIGH FAULT HANDLING LOSC CHANNEL FAULT CHANNEL ENABLE 40kHz TO 80kHz OSCILLATOR (±5%) LCM LAMP CURRENT MONITOR EXTERNAL RESISTOR LAMP FREQUENCY SET CCFL CONTROLLER (SEE THE CCFL CHANNEL BLOCK DIAGRAM) PWM_EN ANALOG LAMP BRIGHTNESS CONTROL (PWM_EN = 0) BRIGHT SLOPE PWM LAMP BRIGHTNESS CONTROL (PWM_EN = 1) EXTERNAL RESISTOR BURST-DIMMING FREQUENCY SET POSC POSITIVE OR NEGATIVE SLOPE SELECT 80Hz TO 300Hz OSCILLATOR (±5%) MUX RAMP GENERATOR OVD OVERVOLTAGE DETECTION GA MOSFET GB GATE DRIVERS DPWM SIGNAL GND 80Hz TO 300Hz _______________________________________________________________________________________ 7 DS3991 Main System Block Diagram Low-Cost CCFL Controller DS3991 CCFL Channel Block Diagram DS3991 LAMP OUT CHANNEL ENABLE 400mV CHANNEL FAULT LCM LAMP CURRENT MONITOR LAMP OVERCURRENT 2.0V BURST-DIMMING PWM SIGNAL DIGITAL CCFL CONTROLLER LAMP STRIKE AND REGULATION 64 LAMP CYCLE INTEGRATOR OVERVOLTAGE OVD OVERVOLTAGE DETECTOR LAMP MAXIMUM VOLTAGE REGULATION LAMP FREQUENCY (40kHz TO 80kHz) 1.0V 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. 8 1.0V GA GB MOSFET GATE DRIVERS 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. _______________________________________________________________________________________ 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. 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 = 4000kΩ x kHz for lamp frequency calculations, K = 4kΩ 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 kΩ x kHz. For the lamp frequency resistor (RLOSC) calculation, K = 4000 kΩ 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 RPOSC = 4k kHz = 25k 0.160kHz 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. R + R2 VTRIP = 2.0 1 R1 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 _______________________________________________________________________________________ 9 DS3991 Low-Cost CCFL Controller VINV VINV R2 VTRIP R2 SVML SVMH DS3991 R1 VTRIP R1 2.0V 2.0V Figure 2. Setting the SVML and SVMH Threshold Voltages DEVICE AND INVERTER SUPPLIES AT PROPER LEVELS? FAULT STATE (MUST POWER CYCLE THE DS3991 OR TAKE SVML BELOW 2V OR SVMH ABOVE 2V TO RESET THE CCFL CONTROLLER) YES LAMP OVERCURRENT (INSTANTANEOUS) 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) 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 ______________________________________________________________________________________ Low-Cost CCFL Controller • VCC drops below the UVLO threshold • SVML input drops below 2.0V • SVMH input goes above 2.0V 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. Table 1. Transformer Specifications (as used in the Typical Operating Circuits) PARAMETER Turns Ratio (Secondary/Primary) Push-Pull Type CONDITIONS MIN (Notes 1, 2, 3) UNITS 80 kHz 80 40 Output Power Output Current 5 Primary DCR MAX 40 Turns Ratio (Secondary/Primary) Half-Bridge Type (Note 3) Frequency TYP Center tap to one end 200 6 W 8 mA m Secondary DCR 500 Primary Leakage 12 μH Secondary Leakage 185 mH Primary Inductance 70 μH 500 mH Secondary Inductance Secondary Output Voltage 1000ms (min) 2000 Continuous 1000 VRMS 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 DS3991 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: 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%) SVML VCC VCC VCC VCC SVMH DS3991 ANALOG LAMP BRIGHTNESS CONTROL BRIGHT DUAL POWER MOSFET PWM_EN SLOPE CCFL LAMP GA LOSC TRANSFORMER RESISTOR SET LAMP FREQUENCY PWM LAMP BRIGHTNESS CONTROL (OPTIONAL) RESISTOR SET BURST-DIMMING FREQUENCY 12 GB POSC/PWM OVD LCM OVERVOLTAGE DETECTION LAMP CURRENT MONITOR GND ______________________________________________________________________________________ Low-Cost CCFL Controller Typical Half-Bridge Application ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V ±10%) INVERTER SUPPLY VOLTAGE (5V ±10% TO 24V ±10%) SVML VCC VCC VCC VCC SVMH DS3991 ANALOG LAMP BRIGHTNESS CONTROL BRIGHT PWM_EN SLOPE GA CCFL LAMP LOSC TRANSFORMER RESISTOR SET LAMP FREQUENCY GB DUAL POWER MOSFET PWM LAMP BRIGHTNESS CONTROL (OPTIONAL) POSC/PWM RESISTOR SET BURST-DIMMING FREQUENCY OVD LCM OVERVOLTAGE DETECTION LAMP CURRENT MONITOR GND ______________________________________________________________________________________ 13 DS3991 Typical Operating Circuits (continued) 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%) SVML VCC VCC VCC VCC SVMH DUAL POWER MOSFET DS3991 CCFL LAMP A GA ANALOG LAMP BRIGHTNESS CONTROL BRIGHT GB +5V CCFL LAMP B PWM_EN SLOPE LCM 2N3904 +5V CCFL LAMP C LOSC RESISTOR SET LAMP FREQUENCY 2N3904 +5V POSC/PWM RESISTOR SET BURST-DIMMING FREQUENCY 2N3904 GND 14 OVD ______________________________________________________________________________________ Low-Cost CCFL Controller Typical Half-Bridge Application, Multiple Lamps Per Channel ON = OPEN OFF/RESET = CLOSED DEVICE SUPPLY VOLTAGE (5V ±10%) INVERTER SUPPLY VOLTAGE (5V ±10% TO 24V ±10%) SVML VCC VCC VCC VCC SVMH DS3991 CCFL LAMP A GA ANALOG LAMP BRIGHTNESS CONTROL BRIGHT GB DUAL POWER MOSFET +5V CCFL LAMP B PWM_EN SLOPE LCM 2N3904 +5V CCFL LAMP C LOSC RESISTOR SET LAMP FREQUENCY 2N3904 +5V POSC/PWM RESISTOR SET BURST-DIMMING FREQUENCY 2N3904 GND OVD ______________________________________________________________________________________ 15 DS3991 Typical Operating Circuits (continued) DS3991 Low-Cost CCFL Controller 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 0.01µF or 0.1µF. 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 DOCUMENT NO. 16 SO (150 mils) 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 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.