ML4835

July 2000 PRELIMINARY ML4835* Compact Fluorescent Electronic Dimming Ballast Controller GENERAL DESCRIPTION The ML4835 is a complete solution for a dimmable or a non-dimmable, high power factor, high efficiency electronic ballast especially tailored for a compact fluorescent lamp (CFL). The Bi-CMOS ML4835 contains controllers for “boost” type power factor correction as well as for a dimming ballast with end-of-lamp life detection. The PFC circuits uses a new , simple PFC topology which requires only one loop for compensation. In addition, this PFC can be used with either peak- or average-current mode. This system produces a power factor of better than 0.99 with low input current THD. The ballast controller section provides for programmable starting sequence with individual adjustable preheat and lamp out-of-socket interrupt times. The ML4835 provides a shut down for both PFC and ballast controllers in the event of end-of-life for the CFL. FEATURES s s s s s s s s s s Power detect for end-of-lamp-life detection Low distortion , high efficiency continuous boost, peak or average current sensing PFC section Leading- and trailing-edge synchronization between PFC and ballast One to one frequency operation between PFC and ballast Programmable start scenario for rapid/instant start lamps Triple frequency control network for dimming or starting to handle various lamp sizes Programmable restart for lamp out condition to reduce ballast heating. Internal over-temperature shutdown PFC over-voltage comparator eliminates output “runaway” due to load removal Low start-up current; < 0.55mA (* Indicates Part is End Of Life as of July 1, 2000) BLOCK DIAGRAM 13 4 3 2 PVFB/OVP 1 RSET RT/CT RT2 CRAMP PIFBO PIFB PEAO POWER FACTOR CONTROLLER ANTI-FLASH COMPENSATION AND POWER DIMMING LEVEL INTERFACE CONTROL AND GATING LOGIC INTERRUPT 10 LAMP FB 5 LEAO 6 OUT A VARIABLE FREQUENCY OSCILLATOR THREE-FREQUENCY CONTROL SEQUENCER VCO PRE-HEAT AND INTERRUPT TIMERS END-OF-LAMP DETECT AND POWER SHUTOFF UNDER-VOLTAGE AND THERMAL SHUTDOWN AGND REF 14 20 VCC 19 LAMP OUT DETECT AND AUTOMATIC LAMP RESTART RX/CX 11 OUTPUT DRIVERS 17 OUT B 16 PFC OUT 18 PGND 15 7 9 8 PWDET 12 1 ML4835 PIN CONFIGURATION ML4835 20-Pin SOIC (S20) 20-Pin DIP (P20) PVFB/OVP PEAO PIFB PIFBO LAMP FB LEAO RSET RT2 RT/CT INTERRUPT 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 REF VCC PFC OUT OUT A OUT B PGND AGND CRAMP PWDET RX/CX PIN DESCRIPTION PIN NAME FUNCTION PIN NAME FUNCTION 1 2 3 PVFB/OVP PEAO PIFB Inverting input to the PFC error amplifier and OVP comparator input. PFC error amplifier output and compensation node 10 INTERRUPT Input used for lamp-out detection and restart. A voltage less than 1V will reset the IC and cause a restart after a programmable interval. RX/CX PWDET CRAMP AGND PGND OUT B OUT A PFC OUT VCC REF Sets the timing for preheat and interrupt. Lamp output power detection Integrated voltage of the error amplifier out Analog ground Power ground. Ballast MOSFET driver output Ballast MOSFET driver output Power factor MOSFET driver output Positive supply voltage Buffered output for the 7.5V reference 11 Senses the inductor current and peak current sense point of the PFC cycle by cycle current limit Output of the current sense amplifier. Placing a capacitor to ground will average the inductor current. Inverting input of the lamp error amplifier, used to sense and regulate lamp arc current. Also the input node for dimmable control. Output of the lamp current error transconductance amplifier used for lamp current loop compensation External resistor which SETS oscillator FMAX, and RX/CX charging current Oscillator timing component to set start frequency Oscillator timing components 12 13 14 5 LAMP FB 15 16 17 18 19 20 4 PIFBO 6 LEAO 7 8 9 R SET RT2 RT/CT 2 ML4835 ABSOLUTE MAXIMUM RATINGS Absolute maximum ratings are those values beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. Supply Current (ICC) ............................................................. 65mA Output Current, Source or Sink (OUT A, OUT B, PFC OUT) DC ........................... 250mA PIFB Input Voltage ............................................–3V to 2V Maximum Forced Voltage (PEAO, LEAO) ............................................ –0.3V to 7.7V Maximum Forced Current (PEAO, LEAO) ...................................................... ±20mA Junction Temperature .............................................. 150ºC Storage Temperature Range ...................... –65ºC to 150ºC Lead Temperature (Soldering, 10 sec) ..................... 260ºC Thermal Resistance (qJA) ML4835CP .......................................................... 65ºC/W ML4835CS .......................................................... 80ºC/W OPERATING CONDITIONS Temperature Range ....................................... 0°C to 85°C ELECTRICAL CHARACTERISTICS Unless otherwise specified, VCC = VCCZ –0.5V, RSET = 11.8kW, RT = 15.4kW, RT2 = 67.5kW, CT = 1.5nF, TA = Operating Temperature Range (Note 1) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS LAMP CURRENT AMPLIFIER (LAMP FB, LEAO) Input Bias Current Small Signal Transconductance Input Bias Voltage Output Low Output High Source Current Sink Current LAMP FB = 3V, RL = ¥ LAMP FB = 2V, RL = ¥ LAMP FB = 0V, LEAO = 6V LAMP FB = 5V, LEAO = 0.3V 7.1 -80 80 35 -0.3 0.2 7.5 -220 220 -0.3 75 -1.0 105 5.0 0.4 µA µ V V V µA µA PFC VOLTAGE FEEDBACK AMPLIFIER ( PEAO, PVFB/OVP) Input Bias Current Small Signal Transconductance Input Bias Voltage Output Low Output High Source Current Sink Current PFC CURRENT-LIMIT COMPARATOR (PIFB) Current-Limit Threshold Propagation Delay PFC OVP COMPARATOR OVP Threshold Hysteresis Propagation Delay 2.65 0.14 2.75 0.20 1.4 2.85 0.30 V V µs 100mV Step and 100mV Overdrive -0.9 -1.0 100 -1.1 V ns PVFB = 3V, RL = ¥ PVFB = 2V, RL = ¥ PVFB = 0V, PEAO = 6V PVFB = 5V, PEAO = 0.3V 6.4 -80 80 35 -0.3 0.2 6.8 220 220 -0.3 75 -1.0 105 5.0 0.4 µA µ V V V µA µA W W 3 ML4835 ELECTRICAL CHARACTERISTICS SYMBOL OSCILLATOR Initial Accuracy (FMIN) Voltage Stability (FMIN) Temperature Stability (FMIN) Total Variation (FMIN) Initial Accuracy (START) Voltage Stability (START) Temparature Stability (START) Total Variation (START) Ramp Valley to Peak Initial Accuracy (Preheat) Total Variation (Preheat) CT Discharge Current Output Drive Deadtime REFERENCE BUFFER Output Voltage Line Regulation Load Regulation Temperature Stability Total Variation Long Term Stabilty Short Circuit Current RSET Voltage 2.4 Line, Load, Temperature Tj=125ºC, 1000 hrs 7.35 5 40 2.5 2.6 TA = 25ºC, IO = 0mA VCCZ – 4V < VCC < VCCZ – 0.5V 1mA < IO < 10mA 7.4 7.5 10 2 0.4 7.65 7.6 25 15 V mV mV % V mV mA V TA = 25ºC Line, Temperature VRTCT = 2.5V CT = 1.5nF 60.8 60.8 6.0 Line, Temperature 49 2.5 64 64 7.5 0.7 67.2 67.2 9.0 Line, Temperature TA = 25ºC 39.2 49 50 0.3 0.3 51 TA = 25ºC VCCZ – 4V < VCC < VCCZ – 0.5V 39.2 40 0.3 0.3 40.8 51 40.8 kHz % % kHz kHz % % kHz V kHz kHz mA us PARAMETER (Continued) CONDITIONS MIN TYP MAX UNITS 4 ML4835 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER (Continued) CONDITIONS MIN TYP MAX UNITS PREHEAT AND INTERRUPT TIMER (RX = 346kW, CX = 10µF) Initial Preheat Period Subsequenct Preheat Period Interrupt Period RX/CX Charging Current RX/CX Open Circuit Voltage RX/CX Maximum Voltage Preheat Lower Threshold Preheat Upper Threshold Start Period End Threshold Interrupt Disable Threshold Hysteresis Input Bias Current POWER SHUTDOWN Power Shutdown Voltage OUTPUTS (OUT A, OUT B, PFC OUT) Output Voltage Low IOUT = 20mA IOUT = 200mA Output Voltage High Output Voltage High Output Voltage Low in UVLO Output Rise and Fall Time UNDER VOLTAGE LOCKOUT AND BIAS CIRCUITS IC Shunt Voltage (VCCZ) Start-up Threshold (VCC START) Hysteresis Start-up Current Interrupt Current Operating Current Shutdown Temperature Hysteresis Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions. 0.86 0.72 5.9 -50 0.4 7.0 1.6 4.4 6.2 1.1 0.16 -54 0.7 7.3 1.75 4.65 6.6 1.25 0.26 -58 1.0 7.8 1.9 4.9 6.9 1.4 0.36 1 s s s µA V V V V V V V µA 0.9 1 1.1 V 0.1 1.0 VCC-0.2 VCC-2.0 VCC-0.1 VCC-1.0 0.2 2.0 V V V V IOUT = 20mA IOUT = 200mA IOUT = 10mA, VCC < VCC START CL=1000pF 0.2 50 V ns ICC=15mA 14.0 14.8 15.5 V V V µA µA mA ºC ºC VCCZ-1.5 VCCZ-1.0 VCCZ-0.5 3.0 VCC START –0.2V (VCC–0.5V), INTERRUPT = 0V (VCC–0.5V) 3.7 350 500 5.5 130 30 4.4 550 750 8.0 5 ML4835 FUNCTIONAL DESCRIPTION The ML4835 consists of peak or average current controlled continuous boost power factor front end section with a flexible ballast control section. Start-up and lampout retry timing are controlled by the selection of external timing components, allowing for control of a wide variety of different lamp types. The ballast section controls the lamp power using frequency modulation (FM) with additional programmability provided to adjust the VCO frequency range. This allows for the IC to be used with a variety of different output networks. Figure 1 depicts a detailed block diagram of ML4835. The ML4835 provides several safety features. See the corresponding sections for more details: • End-of-lamp life detection to detect EOL and shut-off lamps; See End Of Life Section. • Thermal shutdown for temperature sensing extremes; See IC Bias, Under-Voltage Lockout and Thermal Shutdown Section. • Relamping starting with anti-flash for programmable restart for lamp out conditions while minimizing “flashing” when powering from full power to dimming levels; See Starting, Re-Start, Preheat and Interrupt Section REF 20 19 14 VCC AGND REF 6.75V + – REF_OK THERMAL SHUTDOWN TEMP 130ºC/100ºC OUT A 17 + – OUT B 16 PGND – Q UVLO Q R PWDET S + – 15 12 1.0V 14V + 13 1 CRAMP PREHEAT PVFB/OVP – + + COMP V TO 2.5V PEAO 2 PIFBO 4 PIFB 3 PFC OUT 18 + I 4.75V/ 1.75V Q Q S R 1.25V/1V INTERRUPT 10 – – – + – RX/CX 6.75V/1.25V R S Q Q CLK1 Q T Q ÷2 + RT2 8 + –1V 2.75V PVFB RX/CX + – – R ILIM S Q Q PFC CONTROLLER CLK OSCILLATOR RT/CT 9 OVP LEAO 6 LAMP FB – 11 7 V TO I RSET + 5 2.5V V TO I Figure 1. Detailed Block Diagram 6 ML4835 FUNCTIONAL DESCRIPTION (Continued) POWER FACTOR SECTION The ML4835 power factor section is a peak or average current sensing boost mode PFC control circuit in which only voltage loop compensation is needed. It is simpler than a conventional average current control method. It consists of a voltage error amplifier, a current sense amplifier (no compensation is needed), an integrator, a comparator, and a logic control block. In the boost topology, power factor correction is achieved by sensing the output voltage and the current flowing through the current sense resistor. Duty cycle control is achieved by comparing the integrated voltage signal of the error amplifier and the voltage across RSENSE. The duty cycle control timing is shown in Figure 3. The ML4835 implements a triple frequency operation scheme: programmable three-frequency sequence for preheat, ignition, and dimming, that extends lamp life, simplifies lamp network design, and starts lamps at any dimming level without flashing. This addresses the need for a high-Q network for starting sequence and low-Q network for operation, minimizing parasitic losses and improving overall power efficiency. The values for the pre-heat, start, operation, and restart can be programmed or selected (Figure 2). PREHEAT SET TIME VALUES FOR PREHEAT, START AND OPERATION, AND RESTART f1 ML4835 HIGH Q LOW Q f2 START f3 OPERATION Figure 2. Three Frequency Design Model L SW2 RA VOUT LAMP INVERTER LAMP NETWORK EMI FILTER RSENSE SW1 RB LAMP 3 PIFB –A PIFBO 4 + 18 PFC OUT 1 PVFB/OVP R Q – S PIFBO OSC RAMP V TO I + CLK CRAMP 13 CRAMP 2 R1 C2 C1 PEAO VREF1 CLK PEAO – PFC OUT Figure 3. ML4835 PFC Controller Section 7 ML4835 FUNCTIONAL DESCRIPTION (Continued) OVERVOLTAGE PROTECTION AND INHIBIT The OVP pin serves to protect the power circuit from being subjected to excessive voltages if the load should change suddenly (lamp removal). A divider from the high voltage DC bus sets the OVP trip level. When the voltage on PVFB/OVP exceeds 2.75V, the PFC transistor are inhibited. The ballast section will continue to operate. TRANSCONDUCTANCE AMPLIFIERS CRAMP PEAO MAX (1 - D)Ts - Dt = 22K Setting minimum input voltage for output regulation can be achieved by selecting CRAMP as follows for peak current mode: CRAMP = PEAO MAX (1 - D)Ts - Dt 22K : ? ! V - 2VIN 2POUT - OUT (1 - D)Ts 8 ´ R SENSE VIN 2L   1   "# $# (1) And for average current mode: : ? ! V 2POUT - OUT (1 - D)Ts 8 ´ R SENSE VIN 2L     1 "# $# (1a) Where Dt is the dead time. The PFC voltage feedback amplifier is implemented as an operational transconductance amplifier. It is designed to have low small signal forward transconductance such that a large value of load resistor (R1) and a low value ceramic capacitor (