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19-1128; Rev 0; 9/96
KIT ATION EVALU ABLE AVAIL
Digitally Controlled CCFL Backlight Power Supplies
____________________________Features
_______________General Description
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.
MAX1610/MAX1611
(R) Direct Digital Control of CCFL Brightness (R) Low Supply Current: 3mA Max Operating
(R) Low-Voltage Operation, Down to 4.5V (R) Internal 26V, 0.7W Power Switch (R) Protection Against Open or Shorted Lamps (R) Supports Isolated Transformer Secondary (R) SMBus Serial Interface (MAX1611) (R) No Flicker at Low Brightness (internal 280Hz (R) High Power-to-Light Efficiency (R) Selectable 290kHz/145kHz Switching Frequency (R) Oscillator SYNC Input (R) 16-Pin Narrow SO Package
______________Ordering Information
PART MAX1610CSE MAX1611CSE TEMP. RANGE 0C to +70C 0C to +70C PIN-PACKAGE 16 Narrow SO 16 Narrow SO
20A Max Shutdown
Winding
current chopping)
________________________Applications
Notebook/Laptop Computers Point-of-Sale Terminals Portable Medical Equipment Instrument Displays
__________________________________________________________Pin Configurations
TOP VIEW
UP 1 DN 2 SHDN 3 SYNC 4 SS 5 CC 6 CSAV 7 MINDAC 8 16 BATT 15 LX 14 BST SDA 1 SCL 2 SMBSUS 3 SYNC 4 SS 5 CC 6 CSAV 7 MINDAC 8 16 BATT 15 LX 14 BST
MAX1610
13 GND 12 VL 11 CS 10 OTP 9 REF
MAX1611
13 GND 12 VL 11 CS 10 OTP 9 REF
SO
SO
________________________________________________________________ Maxim Integrated Products
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
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 = +70C) SO (derate 8.70mW/C above +70C) .........................696mW Operating Temperature Range MAX1610CSE/MAX1611CSE ..............................0C to +70C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = 0C to +70C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SUPPLY AND REFERENCE BATT Input Voltage Range BATT Quiescent Supply Current, Operate Mode BATT Quiescent Supply Current, Shutdown Mode VL Output Voltage, Operate Mode VL Output Voltage, Shutdown Mode REF Output Voltage REF Load Regulation SWITCHING REGULATOR BATT-to-LX Switch On-Resistance LX Switch Off-Leakage Current Oscillator Frequency Oscillator SYNC Pin Synchronization Range SYNC High Pulse Width SYNC Low Pulse Width SYNC Input Current SYNC Input Low Voltage SYNC Input High Voltage Power-Switch Maximum Duty Cycle SS Source Current SS Sink Current SYNC = REF SS = GND SS = 0.5V 4.0 89 2.5 2 91 4.0 5.5 SYNC = GND or VL SYNC = REF SYNC = GND 250 125 240 200 200 -1 1 0.5 290 145 BST - LX = 4.1V 0.7 1.0 10 330 165 350 A kHz kHz ns ns A V V % A mA No load ISOURCE = 100A 4.75V < BATT < 26V 4.25 3.0 1.92 BATT = 25V 4.75 1.5 10 4.5 3.6 2.0 6 26 3 20 4.75 4.75 2.08 20 V mA A V V V mV CONDITIONS MIN TYP MAX UNITS
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Digitally Controlled CCFL Backlight Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(TA = 0C to +70C, BATT = 8.2V, MINDAC = 0V, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DAC AND ERROR AMPLIFIER DAC Resolution MINDAC Input Voltage Range MINDAC Input Bias Current MINDAC Digital PWM Threshold CSAV Input Voltage Range CSAV Regulation Point CSAV Input Bias Current CSAV to CC Voltage-to-Current Converter Transconductance CC Sink Current CC Source Current OPEN AND SHORTED TUBE PROTECTION OTP Voltage Trip Point OTP Input Bias Current CS Overcurrent Cutoff Threshold MAX1610 LOGIC LEVELS SHDN, UP, DN Input Low Voltage SHDN, UP, DN Input High Voltage SHDN, UP, DN Input Bias Current MAX1611 LOGIC LEVELS SMBSUS, SDA, SCL Input Low Voltage SMBSUS, SDA, SCL Input High Voltage SMBSUS, SDA, SCL Input Bias Current SDA Output Low Sink Current VSDA = 0.6V 2.2 -1 6 1 0.8 V V A mA 2.4 -1 1 0.8 V V A Referred to REF GND < OTP < VL OTP rising -20 -1 500 20 1 mV A mV CC = 2V, CSAV = 1V, D/A at 1LSB CC = 2V, CSAV = 1V, D/A at 1LSB CC = 2V, CSAV = 0V, D/A at full scale D/A at full scale D/A at 1LSB -5 85 80 20 0 232 247 12 5 Guaranteed monotonic 5 0 -1 3 1.0 260 1 1 Bits V A V V mV A mho A A CONDITIONS MIN TYP MAX UNITS
MAX1610/MAX1611
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
TIMING CHARACTERISTICS--MAX1610
(Figure 1, TA = +25C, unless otherwise noted.) PARAMETER UP, DN Pulse Width High UP, DN Pulse Width Low UP, DN Pulse Separation Counter Reset Time SYMBOL t1 t2 t3 t4 CONDITIONS MIN 1 1 1 1 TYP MAX UNITS s s s s
TIMING CHARACTERISTICS--MAX1611
(Figures 2 and 3, TA = +25C, unless otherwise noted.) PARAMETER SCL Serial Clock High Period SCL Serial Clock Low Period SCL, SCA Rise Time SCL, SDA Fall Time Start Condition Setup Time Start Condition Hold Time SDA Valid to SCL Rising Edge Setup Time, Slave Clocking in Data SCL Falling Edge to SDA Transition SCL Falling Edge to SDA Valid, Reading Out Data Note 1: Guaranteed by design. SYMBOL tHIGH tLOW tR tF tSU:STA tHD:STA tSU:DAT tHD:DAT tDV (Note 1) (Note 1) (Note 1) 4.7 4 500 0 1 CONDITIONS MIN 4 4.7 1 0.3 TYP MAX UNITS s s s s s s ns ns s
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Digitally Controlled CCFL Backlight Power Supplies
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
REF OUTPUT VOLTAGE vs. REF OUTPUT CURRENT
MAX1610/1611-TOC1
MAX1610/MAX1611
BATT SUPPLY CURRENT vs. BATT VOLTAGE (SHDN = VL)
MAX1610/1611-TOC2
VL OUTPUT VOLTAGE vs. VL OUTPUT CURRENT
SHDN = VL, OTP = 3V 4.5 VL VOLTAGE (V) BATT = 5V 4.0 3.5 3.0 2.5 2.0 BATT = 12V
MAX1610/1611-TOC3
2.2 SHDN = VL, BATT = 5V 2.1 REF OUTPUT VOLTAGE (V) 2.0 1.9 1.8 1.7 1.6 1.5 1 10 100 1000
2.0 SHDN = VL, OTP = 3V 1.8 BATT CURRENT (mA)
5.0
1.6
1.4
1.2 1.0 10000 0 4 8 12 16 20 24 28 REF OUTPUT CURRENT (A) BATT (V)
0
10
20
30
40
VL OUTPUT CURRENT (mA)
VL OUTPUT VOLTAGE vs. VL LOAD CURRENT
MAX1610/1611-TOC4
BATT SUPPLY CURRENT vs. BATT VOLTAGE (SHDN = OV)
MAX1610/1611-TOC5
VL OUTPUT VOLTAGE vs. BATT VOLTAGE (SHDN = OV)
NO LOAD ON VL, SHDN = OV
MAX1610/1611-TOC6
3.70 SHDN = GND 3.65 3.60 VL VOLTAGE (V) 3.55 3.50 3.45 3.40 BATT = 5V 3.35 3.30 0 200 400 600 800 BATT = 12V
10 SHDN = OV 8 BATT CURRENT (A)
5.0 4.5 4.0 VL (V)
6
3.5 3.0
4
2 0 1000 0 4 8 12 16 20 24 28
2.5 2.0 0 4 8 12 16 20 24 28 BATT (V) BATT (V)
VL LOAD CURRENT (A)
VL OUTPUT VOLTAGE vs. BATT VOLTAGE (SHDN = VL)
MAX1610/1611-TOC7
5.0 4.5 4.0 VL (V) 3.5 3.0 2.5 2.0 0 NO LOAD ON VL, SHDN = VL 4 8 12 16 20 24
28
BATT (V)
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
______________________________________________________________Pin Description
PIN MAX1610 1 -- 2 -- 3 -- 4 5 6 7 8 9 10 11 12 13 14 15 16 MAX1611 -- 1 -- 2 -- 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NAME UP SDA DN SCL SHDN SMBSUS SYNC SS CC CSAV MINDAC REF OTP CS VL GND BST LX BATT FUNCTION 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. System Management Bus Serial Data Input and Open-Drain Output 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. System Management Bus Serial Clock Input 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. Soft-Start Pin. A 4A 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. 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. Input to the Voltage-to-Current Converter, which averages the voltage on CSAV using the capacitor on CC. The voltage at MINDAC sets the DAC's minimum-scale output voltage. Tying MINDAC to VL enables the internal 280Hz current-chopping mode. 2.0V Reference Output. Bypass with 0.1F to GND. Open-Tube Protection Comparator. As long as OTP exceeds the reference voltage, the N-channel BATT-to-LX switch is forced off. Low-Side Current-Sense Input. The current-mode regulator terminates the switch cycle when the voltage at CS exceeds REF - CC. 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 0.1F to GND. System Ground Power Input to the High-Side Gate Driver, which switches the internal N-channel MOSFET on and off. Ground Connection for the Internal High-Side Gate Driver; source-connection point for the internal N-channel MOSFET 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.
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
t1 t2 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
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
RW BIT CLOCKED INTO SLAVE ACKNOWLEDGED BIT CLOCK INTO MASTER MOST SIGNIFICANT BIT CLOCKED
SCL
***
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
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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 (150k) and R6 (51k) 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.
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
VIN + C9 16 BATT VL 12 C2 D3 C6 10 L1 C7 D2 6 C3 CC OTP 10 C5 R4 4 9 R5 C8 R6 8 MINDAC SYNC REF CS CSAV GND 11 7 13 R1 R3 Q1 D1 C1 Q2 1 2 R2 34 5 CCFL 6 T1
5 SS C4
MAX1610 MAX1611*
BST LX
R7 14 15
* DIGITAL INTERFACE NOT SHOWN
Figure 4. Typical Floating-Lamp Application Circuit
Table 1. Necessary CCFL Specifications
SPECIFICATION CCFL Minimum Strike Voltage ("Kick-Off Voltage") UNITS VRMS SYMBOL VS DESCRIPTION Although CCFLs typically operate at 550VRMS, a higher voltage is required initially to light up the tube. 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. The maximum root-mean-square AC current through a CCFL is almost always 5mARMS. No DC current is allowed through any CCFL. 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
CCFL Typical Operating Voltage ("Lamp Voltage")
VRMS
VL
CCFL Maximum Operating Current ("Lamp Current") CCFL Maximum Frequency ("Lamp Frequency") DC Power Source Minimum Input Voltage
mARMS
IL
kHz
fL
V
VMIN
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
Table 2. Typical Application Circuit Component Values a) Resistors
SYMBOL R1 R2 R3 R4 R5 R6 R7 VALUE (Note) 510 51k 8.2k 150k 51k 20 TOLERANCE 1% 10% 5% 5% 5% 5% 10% POWER RATING 1/8W 1/8W 1/16W 1/16W 1/16W 1/16W 1/16W
b) Capacitors
SYMBOL C1 C2 C3, C5 C4, C6, C7, C8 C9 VALUE 0.1F (Note 1) (pF) 27nF 0.1F 10F TOLERANCE 20% 10% 20% -20% -50% WORKING VOLTAGE 25V 3kV 25V 25V 35V Ceramic, larger values acceptable Tantalum, low ESR NOTES F 0.001 @ 1kHz High voltage
c) Other Components
SYMBOL Q1, Q2 D1, D3 D2 L1 T1 DESCRIPTION 1A NPN switching transistor, VCEO 50V 50mA silicon diode, VBR 40V 1A Schottky diode, VBR 30V 100H, 1A inductor 6W Royer oscillator transformer, turns ratio 67:1, secondary (pins 10 and 6) : primary (pins 1 and 3), primary magnetizing inductance (LP) of 44H 20% GENERIC PART 2N2222A 1N4148 1N5818 SURFACE-MOUNT PART FMMT619, SOT23 CMPD4448, SOT23 EC10QS04 CDR125-101 CTX110605 MANUFACTURER Zetex Central Nihon Sumida Coiltronics
Note: Component values depend on lamp characteristics. See Table 3 to select values.
Table 3. Selecting Circuit Values for Figure 4
VL (VRMS) 250 250 300 300 450 500 550 600 IL (mARMS) 3 5 3 5 5 5 5 5 C2 22pF 43pF 18pF 36pF 20pF 18pF 18pF 15pF R1 1.21 0.715 1.18 0.681 0.732 0.715 0.665 0.698 VCT (VMAX) 3.63V 3.61V 4.30V 4.14V 6.55V 7.17V 7.29V 8.41V fROY (kHz) MIN 50.3 43.3 52.1 45.6 51.1 52.1 52.5 53.6 TYP 58.6 49.7 61.0 52.8 59.7 61.0 61.8 63.1 MAX 71.8 60.3 75.1 64.7 73.3 75.1 76.7 78.1
Note: fROY = Royer oscillator damped resonant oscillation frequency. T1 primary magnetizing inductance (LP) = 44H 20%. VCT = average voltage from the T1 center tap to the emitters of Q1 and Q2 (ignoring Q1, Q2 VCE,SAT). C1 = 0.1F 20%; C2 = 10% tolerance; R1 = 1% tolerance. 10 ______________________________________________________________________________________
Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
FIGURE 4 CIRCUIT, C2 = 15pF, IR1 = 462mA, CCFL VL = 500VRMS 3V 6V T1 CENTER-TAP VOLTAGE BATT = 10V, IBATT = 0.20A, MINDAC = 0.5V, D/A VALUE = 11111 0V 1A C1 CURRENT -1A FIGURE 4 CIRCUIT, C2 = 15pF, R1 = 545, CCFL VL = 500VRMS, BATT = 15V, MINDAC = 0.5V, D/A VALUE = 10000 SS VOLTAGE 0V 6V T1 CENTER-TAP VOLTAGE 0V
5s/div
10ms/div
Figure 5. Royer Oscillator Typical Operating Waveforms for Circuit of Figure 4
REF / 8 = 250mV FULL-SCALE
Figure 6. Start-Up Waveforms for Circuit of Figure 4
CSAV REGULATION VOLTAGE
MID-SCALE
MIN-SCALE = MINDAC / 8
OmV 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 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
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Digitally Controlled CCFL Backlight Power Supplies
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
MAX1610/MAX1611
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 = 85 2C3
where BW is the bandwidth of the CSAV regulation loop in kHz, and C3 is the capacitance from CC to GND in nF.
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.
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 4A 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
Block Diagram of the Analog Section
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 SECONDARY VOLTAGE (PIN 10-PIN 6)
T1 PRIMARY CENTER-TAP VOLTAGE (PIN 2)
VCT 2
NVCT 2
-NVCT 2 2
2
NOTE: VCT = AVERAGE VOLTAGE FROM THE T1 CENTER TO THE EMITTERS OF Q1 AND Q2 (IGNORING Q1, Q2 VCE, SAT). = 2fROY.
Figure 8. Transformer Primary/Secondary Voltage Relationship
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
BATT BST DMOS POWER SWITCH LX CS CSAV VL LEVEL SHIFTER 4.5V REG GND
CC
GM /8
REF
MINDAC
(NOTE)
+ 2.0V -
5-BIT DAC
SYNC
OSC
/5
R
S 4A
Q
SS
OTP 5 UP (SDA) DN (SCL) SHDN (SMBSUS) ( ) ARE FOR MAX1611 NOTE: CIRCUITRY TO DETECT MINDAC = VL NOT SHOWN. SEE CHOPPING THE LAMP CURRENT SECTION. DIGITAL INTERFACE
Figure 9. Functional Diagram
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
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 SDA REGSEL SLAVE PULLS SDA LOW STDBY-0 D4-0 D3-0 D2-0 D1-0 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 SDA SLAVE PULLS SDA LOW STDBY-1 D4-1 D3-1 D2-1 D1-1 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 10A 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
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(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 500A 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 (SMBusTM) 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
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Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
CONTROL LOGIC
OTPOK
8 SCL 8-BIT SHIFT REGISTER SDA IN DATA LE
7
LE 7-BIT LATCH-0 7-BIT LATCH-1
LE
7
7 CLR S
VL
SMBSUS
S
A B MULTIPLEXER Y = A WHEN S IS LOW Y 7 D_ SHDNB STDBY
Q
OTPOK REF PRE R OTP OTP COMPARATOR
5
5-BIT DAC
SS CIRCUITRY
BIAS GENERATORS
Figure 12. MAX1611 Serial-Interface Circuitry Block Diagram
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15
Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
Table 4. MAX1611 Configuration Byte with REGSEL = 0
BIT 7 NAME REGSEL POR STATE* -- DESCRIPTION Register Select. A zero in this bit writes the remaining seven bits into the 7-bit latch-0 (Figure 13). 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. 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.
6
SHDNB-0
0
5
STDBY-0
0
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 7 NAME REGSEL POR STATE* -- DESCRIPTION Register Select. A one in this bit writes the remaining seven bits into the 7-bit latch-1 (Figure 13). 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. 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.
6
SHDNB-1
1
5
STDBY-1
1
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
MOST SIGNIFICANT ADDRESS BIT START CONDITION LEAST SIGNIFICANT SLAVE ADDRESS BIT ACKNOWLEDGE MOST SIGNIFICANT R/W BIT DATA BIT
SCL
SDA SLAVE PULLS SDA LOW
OTPOK
DA4
DA3
DA2
DA1
DA0
MAX1611 DRIVES SDA
Figure 13. MAX1611 Serial-Interface Read Example
Table 6. MAX1611 Status Bits
BIT NAME POR STATE* 1 -- -- FUNCTION 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. Unused. These bits always return a logic one.
7 6 5 4 3 2 1 0
OTPOK -- -- 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.
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 0.1F. Also, insert a 330 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
_______ 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
______________________________________________________________________________________
Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
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. tance in the Royer resonant tank. Table 8 lists suppliers for the high-voltage ballast capacitor, C2.
__________ 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 0.68 10% to set a peak current limit of about 735mA. Use a 107 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 = 0.1F, C2 = 15pF, MID-SCALE SETTING, D/A VALUE = 10000 15V
T1 CENTER-TAP VOLTAGE
0V 500s/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 inducVIN 16 + C9 BATT VL 12 D3 C6 T1 R7 BST LX 6 C3 14 15 C7 D2 CC OTP 10 C5 R4 4 9 R5 C8 R6 8 MINDAC SYNC REF CS CSAV GND 11 7 13 R3 D1 L1
Figure 14. Chopped Waveforms
C2 CCFL 10 6
5 SS C4
MAX1610 MAX1611
1
2
34
5
R2 C1 Q1 Q2
D40 R1 R40
D41
Figure 15. Directly Regulating the CCFL Current
18 ______________________________________________________________________________________
Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
Table 7. Capacitor C1 Supplier Information
PART SMD7.3104 SUPPLIER WIMA LOCATION Elmsford, NY Germany Hong Kong CHEV0025J104 PACCOM Electronics NOVACAP Redmond, WA PHONE 914-347-2474 (0621) 8785-0 5-70-11-51 206-883-9200 FAX 914-347-7230 (0621) 8710457158 58-06-84-74 206-881-6959 NOTES/CONTACT Dissipation factor (tan ) at 1kHz and 20C 0.008. Dissipation factor (tan ) at 1kHz 0.002. Dissipation factor (tan ) at 1kHz and 20C 0.0015.
4040N104M250
Valencia, CA
805-295-5920
805-295-5928
Table 8. Capacitor C2 Supplier Information
PART SUPPLIER LOCATION Olean, NY 1808HA330KATMA AVX/Kyocera Vancouver, WA Germany Hong Kong Smyrna, GA GHM1040SL330J3K 302C1812A330K 302R29N330K Murata Metuchen Capacitors, Inc. Johanson Dielectrics Germany Taiwan Old Bridge, NJ Sylmar, CA PHONE 716-372-6611 206-696-2840 08131 9004-0 852-363-3303 404-436-1300 49-911-66870 886-2-562-4218 908-679-3366 818-364-9800 FAX 716-372-6316 206-695-5836 08131 9004-44 852-765-8185 404-436-3030 49-911-6687193 886-2-536-6721 908-679-3222 818-364-6100
___________________Chip Information
TRANSISTOR COUNT : 5457
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19
Digitally Controlled CCFL Backlight Power Supplies MAX1610/MAX1611
________________________________________________________Package Information
DIM 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 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
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
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 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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