LT1768 LINER [Linear Technology], LT1768 Datasheet
LT1768
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LT1768 Summary of contents
Page 1
... It is designed to provide maximum flexibility with a minimum number of external components. The LT1768 is a current mode PWM controller with a 1.5A MOSFET driver for high power applications. It contains a 350kHz oscillator, 5V reference, and a current sense comparator with a 100mV threshold. It operates from 24V input voltage ...
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... Pin Source Current ..................................... 750 A MIN V Pin Source Current ....................................... 10mA REF Operating Junction Temperature Range LT1768C ................................................ 125 C LT1768I ............................................ – 125 C Storage Temperature Range ................. – 150 C Lead Temperature (Soldering 10 sec)................... 300 C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are –100 A, unless otherwise specified. ...
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... Note 7: The PWM frequency is set by the equation PWMFREQ = 22Hz/ MAX C ( F). T Note 8: For VC voltages less than the switching threshold, GATE switching is disabled. Note 9: An open lamp will be detected if either I the threshold current for at least 1 full PWM cycle. LT1768 = 0V 2.5V –100 A, PROG PWM RMAX MIN TYP MAX 0 ...
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... LT1768 W U TYPICAL PERFOR A CE CHARACTERISTICS V vs Temperature REF 5. –1mA REF 5.08 5.06 5.04 5.02 5.00 4.98 4.96 4.94 4.92 4.90 –50 – 100 125 TEMPERATURE ( C) 1768 G01 Supply Current vs Input Voltage INPUT VOLTAGE (V) 1768 G04 SHDN Pull-Up Current vs Input Voltage SHDN ...
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... DIO Pin Voltage vs Current – 2.0 –1.8 –1.6 –1.4 –1.2 –1.0 – 0.8 – 0.6 – 0.4 – 0.2 0 – 2 – 4 – 6 – 8 –10 –12 –14 –16 –18 –20 0 DIO CURRENT (mA) 1768 G20 LT1768 FAULT Pin Saturation Voltage vs Temperature 0.250 0.225 0.200 0.175 0.150 0.125 0.100 0.75 0. DIO1 I ...
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... LT1768 W U TYPICAL PERFOR A CE CHARACTERISTICS VC Clamp Voltage vs Temperature 3. 500 A VC 3.85 3.80 3.75 3.70 3.65 3.60 3.55 3.50 3.45 3.40 50 –50 – 100 125 TEMPERATURE ( C) 1768 G26 PWM Pin Input Current vs Temperature 1. 2.5V PWM 1.30 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 –50 – 100 125 TEMPERATURE ( C) 1768 G29 Ratio vs R DIO1/2 RMAX MAX Current ...
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... PWM cycle, the gate drive will be latched off. The latch can be cleared by setting the PROG voltage to zero or placing the LT1768 in shutdown mode. SENSE (Pin 4): The SENSE pin is the input to the current sense comparator. The threshold of the comparator is a function of the voltage on the VC pin and the switch duty cycle ...
Page 8
... SHDN (Pin 12): The SHDN pin controls the operation of the LT1768. Pulling the SHDN pin above 1.26V or leaving the pin open will result in normal operation of the LT1768. Pulling the SHDN pin below 1V causes a complete shut- down of the LT1768 which results in a typical quiescent current ...
Page 9
... CCFL applications. BASIC OPERATION Referring to the circuit in Figure 1, CCFL current is con- trolled voltage on the PROG pin of the LT1768. The DC voltage on the PROG pin feeds the LT1768’s Multimode Dimming block and is converted to source current into the VC pin. As the VC pin voltage rises, the LT1768’ ...
Page 10
... Royer class converter which provides the CCFLs with a zero DC, 60kHz sinusoidal waveform whose amplitude is based on the average current in L1. Sinusoidal current from both CCFLs is then returned to the LT1768 through the DIO1/2 pins. A fraction of the CCFL current from the negative half of its sine wave pulls against the internal current source at the VC pin closing the loop ...
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... DC controlled CCFL current profile that can be tailored to each particular display. With linear mode CCFL current control over the most widely used current range, and PWM mode at the low end, the LT1768 enables wide dimming ratios while maximizing CCFL lifetimes. Lamp Feedback Current In a typical application, the DIO1/2 pins are connected to the low voltage side of the lamps ...
Page 12
... R PROG maximum allowable current specified by the lamp manu- facturer. The voltage for the PWM pin should then be set so that the LT1768 normally operates in linear mode. A typical value for V is approximately 2.5V, which limits the PWM PWM region to 50% of the V input voltage range. ...
Page 13
... A typical value for the VC capacitor is 0.033 F. For further information on compensation please refer to the references or consult the factory. Current Sense Comparator The LT1768 is a current mode PWM controller. Under normal operating conditions the GATE is driven high at the W U start of every oscillator cycle. The GATE is driven back low when the current reaches a threshold level proportional to the voltage on the VC pin ...
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... PGND GATE Figure 6. Schottky Gate Clamp Reference The internal reference of the LT1768 is a trimmed bandgap reference. The reference is used to power the majority of the LT1768 internal circuitry. The reference is inactive if the LT1768 is in undervoltage lockout, shutdown mode, or thermal shutdown. The undervoltage lockout is active when V is below 7 ...
Page 15
... Ideally, all components in the high current path should be placed as close as possible and connected with short thick traces. The most critical consideration is that T1’s center tap, the Schottky diode D1, LT1768’s V pin, and a low ESR capacitor (C1) be connected directly ...
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... LT1768 AGND 1768 TA04 PWM Intensity Control V R1 REF 49.9k 0 – >5V PROG 1kHz PWM C1 LT1768 10 F AGND PWM Intensity Control From 3. Logic V R1 PROG 10k R1 49. – >3. – >5V AGND VN2222LL 1kHz PWM 1768 TA05 REF LT1768 1768 TA06 ...
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... U TYPICAL APPLICATIONS 2-Wire Serial interface Intensity Control SCL REF PROG SDA V OUT LTC1663 LT1768 GND AGND 1768 TA08 Pushbutton Intensity Control R1 50k S1 CLK1 SHDN V PROG V CLK2 S2 CC LTC1426 AGND V AGND REF R1 49.9k PWM2 PWM1 LT1768 REF LT1768 1768 TA07 17 ...
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... LT1768 U TYPICAL APPLICATIONS 18 ...
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... TYP 0.008 – 0.012 (0.203 – 0.305) LT1768 0.189 – 0.196* (4.801 – 4.978) 0.009 (0.229 REF 0.150 – 0.157** (3.810 – 3.988) ...
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... SMBus Controlled CCFL Switching Regulator Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 4 Watt Single Lamp CCFL Supply 16 GATE REF C5 13 FAULT FAULT 0.1 F LT1768 12 R5 SHDN SHUTDOWN 124k 11 R MIN R4 10 31.6k R MAX 9 R2 PWM 39. ...