19-1128; Rev 0; 9/96 KIT ATION EVALU E L B A AVAIL Digitally Controlled CCFL Backlight Power Supplies The MAX1610/MAX1611 are fully integrated, highefficiency drivers for cold-cathode fluorescent lamps (CCFLs). They operate from a 4.5V to 26V power source. An on-board, high-switching-frequency power MOSFET reduces external component count and magnetics size. The MAX1610/MAX1611 protect against open or shorted lamps. The CCFL can be driven from an isolated transformer secondary winding to improve efficiency and avoid flicker at dim tube settings. Brightness is adjusted by scaling the lamp current, or by operating with a fixed lamp current and chopping the CCFL on and off at a rate faster than the eye can detect. The MAX1610’s digital inputs increment, decrement, or clear an internal, 5-bit up/down counter, which sets CCFL brightness. The MAX1611 uses a System Management Bus (SMBus) 2-wire serial interface to directly set CCFL brightness. Both devices include micropower shutdown and a linear regulator that eliminates the need for a separate logic supply. The digital interface remains active in shutdown, preserving the brightness setting. ________________________Applications Notebook/Laptop Computers ____________________________Features ® Direct Digital Control of CCFL Brightness ® Low Supply Current: 3mA Max Operating 20µA Max Shutdown ® Low-Voltage Operation, Down to 4.5V ® Internal 26V, 0.7W Power Switch ® Protection Against Open or Shorted Lamps ® Supports Isolated Transformer Secondary Winding ® SMBus Serial Interface (MAX1611) ® No Flicker at Low Brightness (internal 280Hz current chopping) ® High Power-to-Light Efficiency ® Selectable 290kHz/145kHz Switching Frequency ® Oscillator SYNC Input ® 16-Pin Narrow SO Package ______________Ordering Information TEMP. RANGE PART PIN-PACKAGE Point-of-Sale Terminals MAX1610CSE 0°C to +70°C 16 Narrow SO Portable Medical Equipment MAX1611CSE 0°C to +70°C 16 Narrow SO Instrument Displays __________________________________________________________Pin Configurations TOP VIEW UP 1 16 BATT SDA 1 16 BATT DN 2 15 LX SCL 2 15 LX SHDN 3 SYNC 4 MAX1610 14 BST SMBSUS 3 13 GND SYNC 4 SS 5 12 VL CC 6 11 CS CSAV 7 10 OTP MINDAC 8 9 SO REF 14 BST MAX1611 13 GND SS 5 12 VL CC 6 11 CS CSAV 7 10 OTP MINDAC 8 9 REF SO ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 MAX1610/MAX1611 _______________General Description MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies ABSOLUTE MAXIMUM RATINGS BATT to GND ............................................................-0.3V to 28V BST to GND ..............................................................-0.3V to 30V BST to LX ....................................................................-0.3V to 6V LX to GND ................................................-0.6V to (BATT + 0.3V) VL to GND...................................................................-0.3V to 6V CS, CSAV, CC, SYNC, REF, MINDAC, SS, OTP to GND............................................-0.3V to (VL + 0.3V) SHDN, UP, DN to GND ...............................................-0.3V to 6V SMBSUS, SDA, SCL to GND ......................................-0.3V to 6V BATT, LX Current .....................................................................1A SDA Current ........................................................................50mA VL Current ...........................................................................50mA Continuous Power Dissipation (TA = +70°C) SO (derate 8.70mW/°C above +70°C) .........................696mW Operating Temperature Range MAX1610CSE/MAX1611CSE ..............................0°C to +70°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C 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. ELECTRICAL CHARACTERISTICS (TA = 0°C to +70°C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 26 V 1.5 3 mA 10 20 µA SUPPLY AND REFERENCE BATT Input Voltage Range BATT Quiescent Supply Current, Operate Mode 4.75 BATT = 25V BATT Quiescent Supply Current, Shutdown Mode VL Output Voltage, Operate Mode 4.75V < BATT < 26V VL Output Voltage, Shutdown Mode REF Output Voltage No load REF Load Regulation ISOURCE = 100µA 4.25 4.5 4.75 V 3.0 3.6 4.75 V 1.92 2.0 2.08 V 6 20 mV 0.7 1.0 Ω 10 µA SWITCHING REGULATOR BATT-to-LX Switch On-Resistance BST - LX = 4.1V LX Switch Off-Leakage Current Oscillator Frequency SYNC = REF 250 290 330 SYNC = GND 125 145 165 Oscillator SYNC Pin Synchronization Range 240 SYNC High Pulse Width 200 ns SYNC Low Pulse Width 200 ns SYNC Input Current SYNC = GND or VL 350 kHz -1 SYNC Input Low Voltage SYNC Input High Voltage 1 µA 0.5 V 4.0 V Power-Switch Maximum Duty Cycle SYNC = REF 89 91 SS Source Current SS = GND 2.5 4.0 SS Sink Current SS = 0.5V 2 2 kHz _______________________________________________________________________________________ % 5.5 µA mA Digitally Controlled CCFL Backlight Power Supplies (TA = 0°C to +70°C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS DAC AND ERROR AMPLIFIER DAC Resolution Guaranteed monotonic 5 Bits MINDAC Input Voltage Range 0 1 V MINDAC Input Bias Current -1 1 µA MINDAC Digital PWM Threshold 3 CSAV Input Voltage Range CSAV Regulation Point 0 D/A at full scale 232 D/A at 1LSB V 1.0 247 260 12 CSAV Input Bias Current -5 5 V mV µA CSAV to CC Voltage-to-Current Converter Transconductance CC = 2V, CSAV = 1V, D/A at 1LSB 85 µmho CC Sink Current CC = 2V, CSAV = 1V, D/A at 1LSB 80 µA CC Source Current CC = 2V, CSAV = 0V, D/A at full scale 20 µA OPEN AND SHORTED TUBE PROTECTION OTP Voltage Trip Point Referred to REF OTP Input Bias Current GND < OTP < VL OTP rising -20 20 mV -1 1 µA CS Overcurrent Cutoff Threshold 500 mV MAX1610 LOGIC LEVELS SHDN, UP, DN Input Low Voltage 0.8 SHDN, UP, DN Input High Voltage 2.4 SHDN, UP, DN Input Bias Current -1 V V 1 µA 0.8 V MAX1611 LOGIC LEVELS SMBSUS, SDA, SCL Input Low Voltage SMBSUS, SDA, SCL Input High Voltage 2.2 SMBSUS, SDA, SCL Input Bias Current SDA Output Low Sink Current -1 VSDA = 0.6V 6 V 1 µA mA _______________________________________________________________________________________ 3 MAX1610/MAX1611 ELECTRICAL CHARACTERISTICS (continued) MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies TIMING CHARACTERISTICS—MAX1610 (Figure 1, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS UP, DN Pulse Width High t1 1 µs UP, DN Pulse Width Low t2 1 µs UP, DN Pulse Separation t3 1 µs Counter Reset Time t4 1 µs TIMING CHARACTERISTICS—MAX1611 (Figures 2 and 3, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS SCL Serial Clock High Period tHIGH 4 µs SCL Serial Clock Low Period tLOW 4.7 µs SCL, SCA Rise Time tR (Note 1) 1 µs SCL, SDA Fall Time tF (Note 1) 0.3 µs Start Condition Setup Time tSU:STA 4.7 µs Start Condition Hold Time tHD:STA 4 µs SDA Valid to SCL Rising Edge Setup Time, Slave Clocking in Data tSU:DAT 500 SCL Falling Edge to SDA Transition tHD:DAT SCL Falling Edge to SDA Valid, Reading Out Data (Note 1) 0 tDV Note 1: Guaranteed by design. 4 ns _______________________________________________________________________________________ ns 1 µs Digitally Controlled CCFL Backlight Power Supplies 1.8 1.9 1.8 1.7 SHDN = VL, OTP = 3V 4.5 VL VOLTAGE (V) 2.0 SHDN = VL, OTP = 3V BATT CURRENT (mA) 1.6 1.4 1.2 1.0 10 100 1000 3.0 2.0 0 4 8 12 16 20 24 28 0 10 20 30 40 BATT (V) VL OUTPUT CURRENT (mA) VL OUTPUT VOLTAGE vs. VL LOAD CURRENT BATT SUPPLY CURRENT vs. BATT VOLTAGE (SHDN = OV) VL OUTPUT VOLTAGE vs. BATT VOLTAGE (SHDN = OV) SHDN = OV 8 BATT = 12V 3.55 3.50 3.45 3.40 3.0 2.5 0 200 400 600 800 3.5 4 3.35 3.30 NO LOAD ON VL, SHDN = OV 4.5 4.0 6 2 BATT = 5V 5.0 VL (V) BATT CURRENT (µA) 3.65 3.60 10 MAX1610/1611-TOC4 SHDN = GND 2.0 0 1000 4 8 12 16 20 24 28 BATT (V) VL LOAD CURRENT (µA) 0 4 8 12 16 20 24 28 BATT (V) VL OUTPUT VOLTAGE vs. BATT VOLTAGE (SHDN = VL) MAX1610/1611-TOC7 5.0 4.5 4.0 VL (V) 0 3.5 REF OUTPUT CURRENT (µA) 3.70 VL VOLTAGE (V) 10000 MAX1610/1611-TOC5 1 BATT = 12V 2.5 1.6 1.5 BATT = 5V 4.0 MAX1610/1611-TOC6 REF OUTPUT VOLTAGE (V) 2.1 5.0 MAX1610/1611-TOC2 SHDN = VL, BATT = 5V VL OUTPUT VOLTAGE vs. VL OUTPUT CURRENT 2.0 MAX1610/1611-TOC1 2.2 BATT SUPPLY CURRENT vs. BATT VOLTAGE (SHDN = VL) MAX1610/1611-TOC3 REF OUTPUT VOLTAGE vs. REF OUTPUT CURRENT 3.5 3.0 2.5 NO LOAD ON VL, SHDN = VL 2.0 0 4 8 12 16 20 24 28 BATT (V) _______________________________________________________________________________________ 5 MAX1610/MAX1611 __________________________________________Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies ______________________________________________________________Pin Description PIN 6 NAME FUNCTION MAX1610 MAX1611 1 — UP — 1 SDA System Management Bus Serial Data Input and Open-Drain Output 2 — DN Logic-Level Input. A rising edge on DN decrements the 5-bit counter for the 5-bit DAC. UP = DN = 1 presets the counter to mid-scale. — 2 SCL System Management Bus Serial Clock Input 3 — SHDN — 3 SMBSUS 4 4 SYNC 5 5 SS Soft-Start Pin. A 4µA current source feeds the capacitor placed on SS. The voltage on this pin limits the peak current in the switch. When the lamp is turned off, SS pulls to GND. 6 6 CC Output of the Voltage-to-Current Converter; Input to the PWM Comparator, which sets the current limit. A capacitor placed at CC sets the current-regulator-loop bandwidth. 7 7 CSAV Input to the Voltage-to-Current Converter, which averages the voltage on CSAV using the capacitor on CC. 8 8 MINDAC The voltage at MINDAC sets the DAC’s minimum-scale output voltage. Tying MINDAC to VL enables the internal 280Hz current-chopping mode. 9 9 REF 2.0V Reference Output. Bypass with 0.1µF to GND. 10 10 OTP Open-Tube Protection Comparator. As long as OTP exceeds the reference voltage, the N-channel BATT-to-LX switch is forced off. 11 11 CS Low-Side Current-Sense Input. The current-mode regulator terminates the switch cycle when the voltage at CS exceeds REF - CC. 12 12 VL Output of the Internal Linear Regulator. VL can be overdriven by a voltage greater than 4.75V to operate the chip from +5V ± 5%, and to conserve power. Bypass with 0.1µF to GND. 13 13 GND System Ground 14 14 BST Power Input to the High-Side Gate Driver, which switches the internal N-channel MOSFET on and off. 15 15 LX Ground Connection for the Internal High-Side Gate Driver; source-connection point for the internal N-channel MOSFET 16 16 BATT Logic-Level Input. A rising edge on UP increments the 5-bit counter for the 5-bit DAC. UP = DN = 1 presets the counter to mid-scale. Logic-Level Shutdown Input Pin. Applying a logic low to SHDN places the chip in a lowsupply-current shutdown mode. System Management Bus Suspend Mode Input. SMBSUS Selects one of two chipconfiguration settings, which are preprogrammed serially. Oscillator Synchronization Input. Tying SYNC to REF sets the oscillator frequency to 290kHz. Tying SYNC to GND or VL lowers the oscillator frequency to 145kHz. 4.5V to 25V Battery-Voltage Input Point. Connects to the internal N-channel power MOSFET’s drain, and to the input of the internal linear regulator that powers the chip. _______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies t2 MAX1610/MAX1611 t1 t4 UP t3 DN Figure 1. MAX1610 UP and DN Signal Timing START CONDITION MOST SIGNIFICANT ADDRESS BIT (A6) CLOCKED INTO SLAVE A5 CLOCKED INTO SLAVE A4 CLOCKED INTO SLAVE A3 CLOCKED INTO SLAVE • • • SCL tHD:STA tLOW tHIGH • • • SDA tSU:STA tSU:DAT tHD:DAT tSU:DAT tHD:DAT Figure 2. MAX1611 SMB Serial-Interface Timing—Address _______________________________________________________________________________________ 7 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies RW BIT CLOCKED INTO SLAVE SCL ACKNOWLEDGED BIT CLOCK INTO MASTER MOST SIGNIFICANT BIT CLOCKED • • • SLAVE PULLING SDA LOW SDA • • • tDV tDV Figure 3. MAX1611 SMB Serial-Interface Timing—Acknowledge _______________Detailed Description Getting Started A cold-cathode fluorescent lamp (CCFL) has two terminals. For the CCFL to emit light, the two lamp terminals must be driven with a high-voltage (approximately 550V AC RMS) and high-frequency (approximately 45kHz) sine wave. The MAX1610/MAX1611 use a varying DC input voltage to create this high-voltage, highfrequency sine-wave drive. To select the correct component values for the MAX1610/MAX1611 circuit, several CCFL parameters and the minimum DC input voltage must be specified; these are listed in Table 1. Table 3 shows the recommended component values to use with the circuit of Figure 4, depending on the particular CCFL parameters. The C2 values in Table 3 have been selected such that the normal operating voltage on the secondary of T1 is as close as possible to the CCFL strike voltage (where the strike voltage (V S ) is assumed to be approximately 1.8 times the CCFL operating voltage (VL)). Components T1, C1, R2, Q1, and Q2 form a Royer oscillator. A Royer oscillator is a resonant tank circuit that oscillates at a frequency dependent on C1, the primary magnetizing inductance of T1 (LP ), and the impedance seen by the T1 secondary. The MAX1610/MAX1611 regulate the current fed into the Royer oscillator by sensing the voltage on R1. For a given current through the Royer oscillator (I R1), the power delivered to the CCFL depends on the Royer oscillator frequency. The R1 values in Table 3 have been selected to ensure that the power into the CCFL 8 does not exceed its maximum rating, despite T1, C1, and C2 component-value variations. The Royer oscillator waveforms for the circuit of Figure 4 are shown in Figures 5 and 6. Analog Circuitry The MAX1610/MAX1611 maintain fixed CCFL brightness with varying input voltages on BATT by regulating the current fed into the Royer oscillator. This current is sensed via resistor R1 between CSAV and GND. An internal switch from BATT-to-LX pulse-width modulates at a fixed frequency to servo the CSAV pin to its regulation voltage. The CSAV regulation voltage can be adjusted via the digital interface to set CCFL brightness. The MAX1610 and MAX1611 differ only in the digital interface they use to adjust the internal 5-bit digital-to-analog converter (DAC) that sets the CSAV regulation voltage. The minimum-scale (min-scale) CSAV regulation voltage is resistor adjustable using the MINDAC pin, setting the minimum CCFL brightness. The D/A setting at MAX1610/MAX1611 power-up is preset to mid-scale (10000 binary) (Figure 7). MINDAC Sets the Minimum Scale The MINDAC pin sets the lowest CCFL brightness level. The voltage at MINDAC is divided by eight, and sets the minimum CSAV regulation voltage. For example, in the circuit of Figure 4, R5 (150kΩ) and R6 (51kΩ) form a resistor divider from REF, which sets MINDAC to 507mV (REF = 2.0V). This sets a minimum CSAV regulation voltage of 63mV with a full-scale CSAV regulation voltage of 247mV. _______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies 16 VL BATT + 12 C2 D3 C9 MAX1610 MAX1611* 5 SS C4 C6 CCFL 10 R7 BST LX 14 15 T1 C7 CC C3 1 2 3 4 5 R2 D1 C1 R3 OTP 6 L1 D2 6 MAX1610/MAX1611 VIN 10 C5 Q1 Q2 R4 4 9 SYNC REF CSAV R5 8 C8 CS MINDAC GND 11 7 R1 13 R6 * DIGITAL INTERFACE NOT SHOWN Figure 4. Typical Floating-Lamp Application Circuit Table 1. Necessary CCFL Specifications SPECIFICATION UNITS SYMBOL DESCRIPTION VRMS VS Although CCFLs typically operate at 550VRMS, a higher voltage is required initially to light up the tube. VRMS VL Once a CCFL has been struck, the voltage required to maintain light output falls to approximately 550VRMS. Small tubes may operate on as little as 250VRMS. The operating voltage of the CCFL stays relatively constant, even as the tube’s brightness is varied. CCFL Maximum Operating Current (“Lamp Current”) mARMS IL The maximum root-mean-square AC current through a CCFL is almost always 5mARMS. No DC current is allowed through any CCFL. CCFL Maximum Frequency (“Lamp Frequency”) kHz fL CCFL Minimum Strike Voltage (“Kick-Off Voltage”) CCFL Typical Operating Voltage (“Lamp Voltage”) DC Power Source Minimum Input Voltage V VMIN The maximum AC-lamp-current frequency. The minimum DC input voltage to the MAX1610/MAX1611 circuit determines the turns ratio required for the DC-AC conversion transformer. Decreasing the minimum input voltage increases the size of the transformer required for a given output power. _______________________________________________________________________________________ 9 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies Table 2. Typical Application Circuit Component Values a) Resistors b) Capacitors TOLERANCE POWER RATING SYMBOL VALUE TOLERANCE WORKING VOLTAGE NOTES (Note) ±1% 1/8W C1 0.1µF ±20% ±25V δF ≤ 0.001 @ 1kHz 510Ω ±10% 1/8W 51kΩ ±5% 1/16W C2 (Note 1) (pF) ±10% ±3kV High voltage R4 8.2kΩ ±5% 1/16W C3, C5 27nF ±20% 25V R5 150kΩ ±5% 1/16W R6 51kΩ ±5% 1/16W C4, C6, C7, C8 0.1µF -20% 25V Ceramic, larger values acceptable R7 20Ω ±10% 1/16W C9 10µF -50% 35V Tantalum, low ESR SYMBOL VALUE R1 R2 R3 c) Other Components SYMBOL DESCRIPTION GENERIC PART SURFACE-MOUNT PART MANUFACTURER Q1, Q2 1A NPN switching transistor, VCEO ≥ 50V 2N2222A FMMT619, SOT23 Zetex D1, D3 50mA silicon diode, VBR ≥ 40V 1N4148 CMPD4448, SOT23 Central D2 1A Schottky diode, VBR ≥ 30V 1N5818 EC10QS04 Nihon L1 100µH, 1A inductor CDR125-101 Sumida T1 6W Royer oscillator transformer, turns ratio 67:1, secondary (pins 10 and 6) : primary (pins 1 and 3), primary magnetizing inductance (LP) of 44µH ±20% CTX110605 Coiltronics Note: Component values depend on lamp characteristics. See Table 3 to select values. Table 3. Selecting Circuit Values for Figure 4 fROY (kHz) VL (VRMS) IL (mARMS) C2 R1 VCT (VMAX) MIN TYP MAX 250 3 22pF 1.21Ω 3.63V 50.3 58.6 71.8 250 5 43pF 0.715Ω 3.61V 43.3 49.7 60.3 300 3 18pF 1.18Ω 4.30V 52.1 61.0 75.1 300 5 36pF 0.681Ω 4.14V 45.6 52.8 64.7 450 5 20pF 0.732Ω 6.55V 51.1 59.7 73.3 500 5 18pF 0.715Ω 7.17V 52.1 61.0 75.1 7.29V 52.5 61.8 76.7 8.41V 53.6 63.1 78.1 550 5 18pF 0.665Ω 600 5 15pF 0.698Ω Note: fROY = Royer oscillator damped resonant oscillation frequency. T1 primary magnetizing inductance (LP) = 44µH ±20%. VCT = average voltage from the T1 center tap to the emitters of Q1 and Q2 (ignoring Q1, Q2 VCE,SAT). C1 = 0.1µF ± 20%; C2 = ±10% tolerance; R1 = ±1% tolerance. 10 ______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies 6V T1 CENTER-TAP VOLTAGE BATT = 10V, IBATT = 0.20A, MINDAC = 0.5V, D/A VALUE = 11111 FIGURE 4 CIRCUIT, C2 = 15pF, R1 = 545Ω, CCFL VL = 500VRMS, BATT = 15V, MINDAC = 0.5V, D/A VALUE = 10000 0V SS VOLTAGE 0V 6V 1A T1 CENTER-TAP VOLTAGE C1 CURRENT -1A 0V 5µs/div 10ms/div Figure 5. Royer Oscillator Typical Operating Waveforms for Circuit of Figure 4 Figure 6. Start-Up Waveforms for Circuit of Figure 4 CSAV REGULATION VOLTAGE REF / 8 = 250mV FULL-SCALE MID-SCALE MIN-SCALE = MINDAC / 8 00000 00001 00010 00011 00100 00101 00110 00111 01000 01001 01010 01011 01100 01101 01110 01111 10000 10001 10010 10011 10100 10101 10110 10111 11000 11001 11010 11011 11100 11101 11110 11111 OmV DAC CODE NOTE: DAC CODE 00000 FORCES THE BATT-TO-LX SWITCH OFF REGARDLESS OF CSAV OR MINDAC VOLTAGE. Figure 7. CSAV Regulation Voltage Range ______________________________________________________________________________________ 11 MAX1610/MAX1611 3V FIGURE 4 CIRCUIT, C2 = 15pF, IR1 = 462mA, CCFL VL = 500VRMS Open-Tube Protection (OTP) Any real transformer used in a Royer oscillator will have a maximum-allowed secondary voltage. If the maximumallowed secondary voltage is exceeded, the winding insulation can break down, leading to permanent transformer damage. The maximum-allowed secondary voltage can be exceeded either when the CCFL drive circuit is turned on without the CCFL being in place, or when the CCFL becomes disconnected during normal operation due to a mechanical failure. To protect against these fault conditions, use the OTP pin to sense the voltage on the transformer center tap (pin 2 of Figure 4). Whenever the voltage on OTP exceeds the REF reference voltage, the BATT-to-LX power switch is forced off. For example, in Figure 4, the CTX110605 transformer has a maximum-allowed continuous secondary voltage of 1340VRMS. D1 and C5 detect the peak voltage on the center tap of T1. R3 and R4 determine the limit on the center tap peak voltage. The relationship between the voltage on the center tap of T1 and the secondary voltage is diagrammed in Figure 8. Neglecting the Q1/Q2 saturation voltage and the voltage on the R1 current-sense resistor yields Equation 1: VCTPK = VSEC 2 2N where VSEC is the maximum root-mean-square voltage allowed on the secondary, N is the secondary-to-primary turns ratio, and VCTPK is the peak voltage on the transformer center tap. Block Diagram of the Analog Section Loop-Compensation Capacitor (CC) The BATT-to-LX switch turns on at fixed frequency, and turns off when the current-sense voltage on the CS pin exceeds CC - REF. As the CC pin voltage rises, the CS current limit rises as well. A transconductance amplifier compares the voltage on CSAV to the desired regulation voltage and outputs a current proportional to this error to the CC pin. A capacitor from CC to GND sets the bandwidth of this regulation loop, as shown in Equation 2: BW = πVCT 2 2π ω 85 2πC3 where BW is the bandwidth of the CSAV regulation loop in kHz, and C3 is the capacitance from CC to GND in nF. Soft Start (SS) Soft start prevents the triggering of OTP upon powerup. Placing a capacitor from SS to GND soft starts the Royer oscillator by slowly raising the CS current-limit voltage. Internal circuitry pulls SS to GND during power-on reset, or whenever the lamp is turned off (DAC = 00000, shutdown mode, ON-1 = 0, or ON-0 = 0) (Figures 10 and 11). When SS is not pulled to GND, an internal 4µA current sources into the capacitor at the SS pin. This pin is internally diode clamped to REF so that it rises to a maximum voltage of about 2.7V. Regardless of the voltage on CC, the CS current-sense voltage is never allowed to exceed the voltage on SS divided by 5. Frequency Selection and Synchronization The SYNC pin performs two functions: it sets the BATTto-LX switching frequency, and it allows the BATT-to-LX switching frequency to be synchronized to an external oscillator. SYNC tied to GND or VL sets a 145kHz switching frequency; SYNC tied to REF sets a 290kHz T1 SECONDARY VOLTAGE (PIN 10–PIN 6) Figure 9 shows a functional diagram of the analog circuitry in the MAX1610/MAX1611. The chips have identical analog circuitry, and differ only in their digital interface. T1 PRIMARY CENTER-TAP VOLTAGE (PIN 2) MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies NπVCT 2 -NπVCT 2 2π ω NOTE: VCT = AVERAGE VOLTAGE FROM THE T1 CENTER TO THE EMITTERS OF Q1 AND Q2 (IGNORING Q1, Q2 VCE, SAT). ω = 2πfROY. Figure 8. Transformer Primary/Secondary Voltage Relationship 12 ______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611 BATT BST VL DMOS POWER SWITCH LEVEL SHIFTER 4.5V REG GND LX CS CSAV Σ GM CC 5-BIT DAC ÷8 REF MINDAC (NOTE) SYNC + 2.0V - ÷5 OSC R S Q 4µA SS OTP 5 UP (SDA) DN (SCL) DIGITAL INTERFACE SHDN (SMBSUS) ( ) ARE FOR MAX1611 NOTE: CIRCUITRY TO DETECT MINDAC = VL NOT SHOWN. SEE CHOPPING THE LAMP CURRENT SECTION. Figure 9. Functional Diagram ______________________________________________________________________________________ 13 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies MOST SIGNIFICANT ADDRESS BIT START CONDITION LEAST SIGNIFICANT SLAVE ADDRESS BIT ACKNOWLEDGE MOST SIGNIFICANT R/W BIT DATA BIT SLAVE ACKNOWLEDGE LEAST SIGNIFICANT DATA BIT SCL SHDNB-0 REGSEL SDA D4-0 D3-0 D2-0 D1-0 STDBY-0 SLAVE PULLS SDA LOW D0-0 SLAVE PULLS SDA LOW Figure 10. MAX1611 Serial-Interface Single-Byte Write Example (REGSEL = 0) MOST SIGNIFICANT ADDRESS BIT START CONDITION LEAST SIGNIFICANT SLAVE ADDRESS BIT ACKNOWLEDGE MOST SIGNIFICANT R/W BIT DATA BIT SLAVE ACKNOWLEDGE LEAST SIGNIFICANT DATA BIT SCL REGSEL SHDNB-1 D4-1 SDA D3-1 D2-1 D1-1 STDBY-1 SLAVE PULLS SDA LOW D0-1 SLAVE PULLS SDA LOW Figure 11. MAX1611 Serial-Interface Single-Byte Write Example (REGSEL = 1) switching frequency. Any rising edge on SYNC restarts a BATT-to-LX switch cycle by forcing the switch on. ________MAX1610 Digital Interface The MAX1610 contains an internal 5-bit up/down counter that sets the value of the internal 5-bit DAC. At power-on, or when both the UP and DN pins are held high simultaneously, the 5-bit up/down counter is preset to 10000 binary, which corresponds to mid-scale. A rising edge on UP increments the 5-bit up/down counter. A rising edge on DN decrements the 5-bit up/down counter. The counter will not roll over on either underflow or overflow. For example, if the CCFL is at maximum intensity level, rising edges on UP will not change the output. The SHDN pin provides a way to lower the MAX1610 supply current to 10µA without resetting the 5-bit up/down counter. With SHDN = 1, the MAX1610 operates normally with VL at 4.5V. When the BATT-to-LX power switch operates, an additional 3mA of current 14 (other than the supply current) is consumed through the BST pin, requiring VL to source at least 4.5mA of current. With SHDN = 0, all analog circuitry turns off, except for a coarse regulator that can source up to 500µA from VL. The coarse regulator preserves the state of the internal logic and keeps the digital interface active during shutdown (SHDN = 0). ________MAX1611 Digital Interface A single byte of data written over the Intel System Management Bus (SMBus™) controls the MAX1611. Figures 10 and 11 show example single-byte writes. The MAX1611 contains two 7-bit latches for storing configuration data. Only one of the 7-bit latches is active at a time. The MAX1611 responds only to its own address, 0101101 binary. The SMBSUS pin selects which of the two sets of configuration data is used. Figure 12 shows a schematic diagram of the MAX1611’s digital circuitry. Notice that the SMBSUS pin selects which one of the ______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611 OTPOK CONTROL LOGIC 8 SCL 8-BIT SHIFT REGISTER SDA IN DATA LE 7 LE LE 7-BIT LATCH-1 7-BIT LATCH-0 7 VL 7 CLR SMBSUS S A B MULTIPLEXER Y = A WHEN S IS LOW Q S OTPOK REF Y PRE 7 R D_ OTP OTP COMPARATOR SHDNB STDBY 5 5-BIT DAC SS CIRCUITRY BIAS GENERATORS Figure 12. MAX1611 Serial-Interface Circuitry Block Diagram ______________________________________________________________________________________ 15 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies Table 4. MAX1611 Configuration Byte with REGSEL = 0 BIT NAME POR STATE* 7 REGSEL — Register Select. A zero in this bit writes the remaining seven bits into the 7-bit latch-0 (Figure 13). DESCRIPTION 6 SHDNB-0 0 Complete Shutdown. Pulling SMBSUS low with SHDNB-0 = 0 places the MAX1611 into a low-quiescent-current shutdown mode, with the reference off and the VL linear-regulator output switched to a low-current, coarse regulation mode. Pulling SMBSUS low with SHDNB-0 = 1 puts the MAX1611 into its normal operational mode, with the reference and internal VL linear regulator fully on. SHDNB-0 supersedes STDBY-0. As long as SHDNB-0 = 0 and SMBSUS = 0, it doesn't matter what STDBY-0 is; the MAX1611 still shuts down. 5 STDBY-0 0 Standby, disables CCFL supply only. As long as SMBSUS stays low and STDBY-0 = 0, the internal power switch is kept off and SS is held shorted to GND; neither the internal reference nor the linear regulator is affected. With STDBY = 1 and SMBSUS low, the MAX1611 operates normally. 4 3 2 1 0 D4-0 D3-0 D2-0 D1-0 D0-0 1 0 0 0 0 DAC Input Data. With the SMBSUS pin low, bits D4-0 through D0-0 set the DAC. * Initial register state after power-up. Table 5. MAX1611 Configuration Byte with REGSEL = 1 BIT NAME POR STATE* 7 REGSEL — Register Select. A one in this bit writes the remaining seven bits into the 7-bit latch-1 (Figure 13). DESCRIPTION 6 SHDNB-1 1 Complete Shutdown. Pulling SMBSUS high with SHDNB-1 = 0 places the MAX1611 into a low-quiescent-current shutdown mode, with the reference off and the VL linear regulator output switched to a low-current coarse regulation mode. Pulling SMBSUS high with SHDNB-1 = 1 puts the MAX1611 into its normal operational mode, with the reference and internal VL linear regulator fully on. SHDNB-1 supersedes STDBY-1. As long as SHDNB-1 = 0 and SMBSUS = 0, it doesn’t matter what STDBY-1 is; the MAX1611 still shuts down. 5 STDBY-1 1 Standby, disables CCFL supply only. As long as SMBSUS stays high and STDBY-1 = 0, the internal power switch is kept off and SS is held shorted to GND; neither the internal reference nor the linear regulator is affected. With STDBY-1 = 1 and SMBSUS high, the MAX1611 operates normally. 4 3 2 1 0 D4-1 D3-1 D2-1 D1-1 D0-1 1 0 0 0 0 DAC Input Data. With the SMBSUS pin high, bits D4-1 through D0-1 set the DAC. * Initial register state after power-up. 16 ______________________________________________________________________________________ Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611 LEAST SIGNIFICANT SLAVE ADDRESS BIT ACKNOWLEDGE MOST SIGNIFICANT R/W BIT DATA BIT MOST SIGNIFICANT ADDRESS BIT START CONDITION SCL OTPOK SDA DA4 DA3 DA2 DA1 DA0 SLAVE PULLS SDA LOW MAX1611 DRIVES SDA Figure 13. MAX1611 Serial-Interface Read Example Table 6. MAX1611 Status Bits BIT NAME POR STATE* FUNCTION 7 OTPOK 1 Latched Open-Tube Detection. OTPOK = 0 indicates that open-tube detection has been triggered. As soon as the voltage on the OTP pin exceeds REF, the OTPOK bit is cleared. Reset the OTPOK pin by entering shutdown or standby. 6 5 — — — — Unused. These bits always return a logic one. 4 3 2 1 0 DA4 DA3 DA2 DA1 DA0 Displays the DAC setting selected by SMBSUS. * Initial register state after power-up. two 7-bit registers is used. Tables 4 and 5 describe the data format for the configuration data. Status information can be read from the MAX1611 using the SMBus read-byte protocol. Figure 13 shows an example status read. Table 6 describes the status information data format. During shutdown (SMBSUS = 0 and SHDNB-0 = 0, or SMBSUS = 1 and SHDNB-1 = 0), the MAX1611 serial interface remains fully functional and can be used to set either the SHDNB-0 or SHDNB-1 bits in order to return the MAX1611 to its normal operational state. _______ Chopping the Lamp Current Chopping the lamp current allows lower sustainable light levels without lamp flicker. Intensity is varied by controlling the on-time duty cycle. Tying MINDAC to VL activates a special mode, which allows the CCFL intensity to be varied by turning the lamp on and off at a frequency faster than the eye can detect. The SS pin pulls to GND during off time and rises to 2.7V during on time. During on time, the CSAV pin regulates to REF / 8 (250mV). During off time, the BATT-to-LX power switch is forced off and the CC compensation node goes high impedance. Omit R5, R6, and C4 of the circuit in Figure 4. In this mode, leave SS floating and increase the CC capacitance to 0.1µF. Also, insert a 330Ω resistor in series with D1 (Figure 4) to prevent the open-lamp detection circuit from being tripped by the repeated striking of the lamp. The SS pin will oscillate at the switching frequency divided by 1024 (283Hz with SYNC = REF). The intensity can be varied with the duty cycle at the SS pin. The duty cycle is set by the DAC in 3% increments. Duty cycle will vary with intensity. Full-scale yields a 100% duty cycle. DAC codes 00001, 00010, and 00011 all yield the ______________________________________________________________________________________ 17 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies tance in the Royer resonant tank. Table 8 lists suppliers for the high-voltage ballast capacitor, C2. minimum 9% duty cycle. DAC code 00000 shuts off the lamp entirely (0% duty cycle). Figure 14 shows the chopped waveforms with the DAC set to mid-scale. __________ Applications Information Directly Regulating the Lamp Current The MAX1610/MAX1611 can directly regulate the CCFL current by tapping into the secondary of T1 (Figure 15). This allows more precise setting of the maximum lamp current (IL). The disadvantage of this approach is that the secondary-to-ground voltage is twice that shown in Figure 4, increasing the likelihood of the thermometer effect, where one end of the lamp is brighter than the other. Figure 15 uses the same component values as Figure 4, except for R1, R40, D40, and D41. D40 and D41 are the same type of diode as D1. R1 should be 0.68Ω ±10% to set a peak current limit of about 735mA. Use a 107Ω ±1% resistor for R40 to set a lamp current of 5mARMS. This circuit accepts a wide range of lamp types without component adjustments. 4V SS VOLTAGE 0V BATT = 15V, MINDAC = VL, SS = OPEN, CC = 0.1µF, C2 = 15pF, MID-SCALE SETTING, D/A VALUE = 10000 15V T1 CENTER-TAP VOLTAGE 0V 500µs/div Component Suppliers Table 7 lists three different sources for C1. C1 requires a low dissipation factor to prevent overheating as energy is cycled between C1 and the T1 magnetizing induc- Figure 14. Chopped Waveforms VIN C2 16 VL BATT + 12 CCFL D3 C9 SS C4 10 R7 BST LX 14 15 CC C3 2 1 L1 5 R2 D1 C1 R3 OTP 3 4 C7 D2 6 6 T1 MAX1610 MAX1611 5 C6 10 Q1 Q2 C5 R4 4 9 SYNC REF CSAV R5 8 C8 CS MINDAC GND D40 11 7 R1 13 R6 Figure 15. Directly Regulating the CCFL Current 18 D41 ______________________________________________________________________________________ R40 Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611 Table 7. Capacitor C1 Supplier Information PART SUPPLIER SMD7.3104 WIMA LOCATION PHONE FAX NOTES/CONTACT Elmsford, NY 914-347-2474 914-347-7230 Germany (0621) 8785-0 (0621) 8710457158 Hong Kong 5-70-11-51 58-06-84-74 Dissipation factor (tan δ) at 1kHz and 20°C ≤ 0.008. CHEV0025J104 PACCOM Electronics Redmond, WA 206-883-9200 206-881-6959 Dissipation factor (tan δ) at 1kHz ≤ 0.002. 4040N104M250 NOVACAP Valencia, CA 805-295-5920 805-295-5928 Dissipation factor (tan δ) at 1kHz and 20°C ≤ 0.0015. Table 8. Capacitor C2 Supplier Information PART SUPPLIER 1808HA330KATMA GHM1040SL330J3K AVX/Kyocera Murata LOCATION PHONE FAX Olean, NY 716-372-6611 716-372-6316 Vancouver, WA 206-696-2840 206-695-5836 Germany 08131 9004-0 08131 9004-44 Hong Kong 852-363-3303 852-765-8185 Smyrna, GA 404-436-1300 404-436-3030 Germany 49-911-66870 49-911-6687193 Taiwan 886-2-562-4218 886-2-536-6721 302C1812A330K Metuchen Capacitors, Inc. Old Bridge, NJ 908-679-3366 908-679-3222 302R29N330K Johanson Dielectrics Sylmar, CA 818-364-9800 818-364-6100 ___________________Chip Information TRANSISTOR COUNT : 5457 ______________________________________________________________________________________ 19 MAX1610/MAX1611 Digitally Controlled CCFL Backlight Power Supplies ________________________________________________________Package Information DIM D 0°-8° A 0.101mm 0.004in. e B A1 E C L Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.) H A A1 B C E e H L INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016 DIM PINS D D D 8 14 16 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27 INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00 21-0041A 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. 20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.