LT3485-0/LT3485-1/ LT3485-2/LT3485-3 Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive U DESCRIPTIO FEATURES The LT®3485 family of photoflash chargers are highly integrated ICs containing complete charger and IGBT drive functions. The patented control technique of the LT3485-x allows it to use extremely small transformers. Output voltage detection requires no external circuitry. The turns ratio of the transformer controls the final charge voltage. While charging, the output voltage on the capacitor may be monitored by a microcontroller from the monitor pin. Each device contains an on-chip high voltage NPN power switch, which can withstand negative voltages on the switch pin without an external Schottky diode. The device features a VBAT pin, which allows the use of two AA cells to charge the capacitor. The internal circuitry operates from the VIN pin. The LT3485-0 has a primary current limit of 1.4A, whereas the LT3485-3, LT3485-2, and LT3485-1 have current limits of 2A, 1A and 0.7A respectively. These different current limits result in tightly controlled input currents. Integrated IGBT Driver Voltage Output Monitor Uses Small Transformers: 5.8mm × 5.8mm × 3mm Operates from Two AA Batteries, Single Cell Li-Ion or Any Supply from 1.8V up to 10V No Output Voltage Divider Needed No External Schottky Diode Required Charges Any Size Photoflash Capacitor Available in 10-Lead (3mm × 3mm) DFN ■ ■ ■ ■ ■ ■ ■ ■ Fast Charge Time VERSION INPUT CURRENT (mA) CHARGE TIME (sec) LT3485-3 750 2.5 LT3485-0 500 3.7 LT3485-2 350 5.5 LT3485-1 225 4.0* VIN = VBAT = 3.6V 100µF capacitor, 320V. *50µF capacitor U APPLICATIO S ■ The CHARGE pin gives full control of the part to the user. Driving CHARGE low puts the part in shutdown. The DONE pin indicates when the part has completed charging. The LT3485 series of parts are housed in a leadless (3mm × 3mm) DFN package. Digital Camera and Cell Phone Flash Charger , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6636021. U TYPICAL APPLICATIO LT3485-0 Photoflash Charger Uses High Efficiency 3mm Tall Transformers DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VBAT 2 AA OR 1 TO 2 Li-Ion • 4 4.7µF 2 • 1M 5 150µF PHOTOFLASH CAPACITOR SW VBAT LT3485-0 Charging Waveform 320V 1:10.2 1 DONE TRIGGER T 1 CHARGE GND 2 LT3485-0 VCC 5V VIN 0.22µF VMONT IGBTPWR IGBTIN A 2.2µF 600V FLASHLAMP VOUT 50V/DIV 3 TO MICRO C IGBT IGBTOUT AVERAGE INPUT CURRENT 0.5A/DIV VIN = 3.6V COUT = 100µF 1s/DIV 3485 TA02 3485 TA01 34850123fb 1 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN Voltage .............................................................. 10V VBAT Voltage ............................................................ 10V SW Voltage ................................................... –1V to 50V SW Pin Negative Current ...................................... –0.5A CHARGE Voltage ...................................................... 10V IGBTIN Voltage ........................................................ 10V IGBTOUT Voltage ..................................................... 10V DONE Voltage .......................................................... 10V IGBTPWR Voltage .................................................... 10V VMONT Voltage ......................................................... 10V Current into DONE Pin ............................... 0.2mA/–1mA Maximum Junction Temperature .......................... 125°C Operating Temperature Range (Note 2) ... –40°C to 85°C Storage Temperature Range .................. –65°C to 125°C TOP VIEW 10 VMONT CHARGE 1 VBAT 2 VIN 3 SW 4 7 IGBTIN SW 5 6 IGBTOUT 9 DONE 11 8 IGBTPWR DD PACKAGE 10-LEAD (3mm ´ 3mm) PLASTIC DFN TJMAX = 125°C θJA = 43°C/W EXPOSED PAD (11) IS GND, MUST BE SOLDERED TO PCB ORDER PART NUMBER DD PART MARKING LT3485EDD-0 LT3485EDD-1 LT3485EDD-2 LT3485EDD-3 LBRH LBVN LBVP LBTK Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted. PARAMETER Quiescent Current CONDITIONS Not Switching VCHARGE = 0V MIN TYP 5 0 MAX 8 1 10 31 1.7 1.2 0.85 0.55 310 210 170 100 31.5 1.8 1.3 0.95 0.65 400 300 225 175 32 A A A A mV mV mV mV V 10 200 45 400 120 mV mV 65 0 100 0.1 µA µA VIN Voltage Range ● 2.5 VBAT Voltage Range ● 1.7 Switch Current Limit VOUT Comparator Trip Voltage LT3485-3 LT3485-0 LT3485-2 LT3485-1 LT3485-3, ISW = 1.5A LT3485-0, ISW = 1A LT3485-2, ISW = 700mA LT3485-1, ISW = 400mA Measured as VSW – VIN VOUT Comparator Overdrive DCM Comparator Trip Voltage 300ns Pulse Width Measured as VSW – VIN CHARGE Pin Current VCHARGE = 3V VCHARGE = 0V Switch VCESAT 1.6 1.1 0.75 0.45 ● ● 10 UNITS mA µA V V 34850123fb 2 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted. PARAMETER Switch Leakage Current CONDITIONS VIN = VSW = 5V, in Shutdown TYP 0.01 100kΩ from VIN to DONE DONE Output Signal Low 33µA into DONE Pin DONE Leakage Current VDONE = 3V, DONE NPN Off 3 ● IGBT Input Voltage High COUT = 4000pF, IGBTPWR = 5V, 10%→90% COUT = 4000pF, IGBTPWR = 5V, 90%→10% SW – VBAT = 20V SW – VBAT = 30V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. V 140 200 mV 20 100 nA 1.5 V ● IGBT Input Voltage Low 0.3 610 920 V µs 20 DONE Output Signal High UNITS µA V 0.3 High→Low→High Monitor Output Current MAX 1 1 ● CHARGE Input Voltage Low IGBT Output Rise Time IGBT Output Fall Time VOUT Monitor Accuracy ● ● CHARGE Input Voltage High Minimum Charge Pin Low Time MIN 450 340 625 940 200 640 960 V ns ns mV mV µA Note 2: The LTC3485E-X is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. 34850123fb 3 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3485-0 curves use the circuit of Figure 8, LT3485-1 curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted. LT3485-1 Charging Waveform LT3485-0 Charging Waveform VOUT 50V/DIV LT3485-2 Charging Waveform VOUT 50V/DIV VOUT 50V/DIV AVERAGE INPUT CURRENT 1A/DIV VIN = 3.6V COUT = 50µF 3485 G01 0.5s/DIV AVERAGE INPUT CURRENT 0.5A/DIV VIN = 3.6V COUT = 50µF LT3485-3 Charging Waveform 3485 G02 0.5s/DIV AVERAGE INPUT CURRENT 0.5A/DIV V = 3.6V IN COUT = 50µF LT3485-0 Input Current Charge Time 6 600 COUT = 50µF LT3485-1 CHARGE TIME (SECONDS) 5 AVERAGE INPUT CURRENT 1A/DIV V = 3.6V IN COUT = 50µF 4 3 2 1 3485 G04 0.5s/DIV 500 LT3485-2 INPUT CURRENT (mA) VOUT 50V/DIV 400 300 200 2.5V 3.6V 4.2V 100 LT3485-0 0 3485 G03 0.5s/DIV 2 3 4 LT3485-3 5 VIN (V) 7 6 0 8 0 50 100 150 200 VOUT (V) 250 1635 G05 LT3485-1 Input Current 3485 G06 LT3485-2 Input Current 250 300 LT3485-3 Input Current 400 900 800 150 100 50 2.5V 3.6V 4.2V 0 0 50 100 150 200 VOUT (V) 250 300 3485 G07 700 300 INPUT CURRENT (mA) INPUT CURRENT (mA) INPUT CURRENT (mA) 200 200 100 2.5V 3.6V 4.2V 0 0 50 100 150 200 VOUT (V) 250 300 3485 G08 600 500 400 300 200 2.5V 3.6V 4.2V 100 0 0 50 100 150 200 VOUT (V) 250 300 3485 G09 34850123fb 4 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3485-0 curves use the circuit of Figure 8, LT3485-1 curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted. LT3485-1 Efficiency LT3485-2 Efficiency 90 80 80 80 70 60 50 40 70 60 50 2.5V 3.6V 4.2V 40 50 100 150 200 VOUT (V) 250 EFFICIENCY (%) 90 EFFICIENCY (%) EFFICIENCY (%) LT3485-0 Efficiency 90 300 100 150 200 VOUT (V) 250 LT3485-0 Output Voltage 321 321 70 320 320 100 150 200 VOUT (V) 250 319 318 2.5V 3.6V 4.2V 50 VOUT (V) 80 VOUT (V) 322 40 150 200 VOUT (V) 250 300 317 300 2 3 4 5 VIN (V) 6 7 319 318 –40°C 25°C 85°C 3485 G13 317 8 –40°C 25°C 85°C 2 3 4 5 VIN (V) 6 7 3485 G14 LT3485-2 Output Voltage 8 3485 G15 LT3485 Switch Current Limits LT3485-3 Output Voltage 328 322 2000 321 1600 VOUT (V) –40°C 25°C 85°C 326 325 CURRENT LIMIT (mA) LT3485-3 327 319 318 323 317 2 3 4 5 VIN (V) 6 7 8 3485 G16 LT3485-0 1200 320 324 322 100 LT3485-1 Output Voltage 322 50 50 3485 G12 90 60 2.5V 3.6V 4.2V 3485 G11 LT3485-3 Efficiency EFFICIENCY (%) 40 300 3485 G10 VOUT (V) 60 50 2.5V 3.6V 4.2V 50 70 3 4 5 VIN (V) 6 7 800 LT3485-1 400 –40°C 25°C 85°C 2 LT3485-2 8 3485 G17 0 –40 –20 40 20 0 60 TEMPERATURE (°C) 80 100 3485 G18 34850123fb 5 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3485-0 curves use the circuit of Figure 8, LT3485-1 curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted. LT3485-1 Switching Waveform LT3485-0 Switching Waveform VSW 10V/DIV VSW 10V/DIV IPRI 1A/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 100V 1µs/DIV 3485 G19 VSW 10V/DIV IPRI 2A/DIV VIN = 3.6V VOUT = 100V 1µs/DIV VSW 10V/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 100V LT3485-3 Switching Waveform LT3485-2 Switching Waveform 3485 G20 1µs/DIV VIN = 3.6V VOUT = 100V 3485 G21 1µs/DIV LT3485-1 Switching Waveform LT3485-0 Switching Waveform VSW 10V/DIV VSW 10V/DIV IPRI 1A/DIV IPRI 1A/DIV 3485 G22 VIN = 3.6V VOUT = 300V LT3485-2 Switching Waveform 3485 G23 1µs/DIV VIN = 3.6V VOUT = 300V 3485 G24 1µs/DIV LT3485-0/LT3485-1/LT3485-2/ LT3485-3 Switch Breakdown Voltage LT3485-3 Switching Waveform VSW 10V/DIV VSW 10V/DIV IPRI 2A/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 300V 1µs/DIV 3485 G25 VIN = 3.6V VOUT = 300V 1µs/DIV 3485 G26 SWITCH CURRENT (mA) 10 SW PIN IS RESISTIVE UNTIL BREAKDOWN 9 VOLTAGE DUE TO INTEGRATED RESISTORS. THIS DOES NOT INCREASE 8 QUIESCENT CURRENT OF PART 7 T = 25°C 6 5 4 T = –40°C T = 85°C 3 2 1 VIN = VCHARGE = 5V 0 0 10 20 30 40 50 60 70 80 90 100 SWITCH VOLTAGE (V) 3485 G27 34850123fb 6 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U U U PI FU CTIO S CHARGE (Pin 1): Charge Pin. A low (<0.3V) to high (>1V) transition on this pin puts the part into power delivery mode. Once the target voltage is reached, the part will stop charging the output. Toggle this pin to start charging again. Bringing the pin low (<0.3V) will terminate the power delivery and put the part in shutdown. VBAT (Pin 2): Battery Supply Pin. Must be locally bypassed with a good quality ceramic capacitor. Battery supply must be 1.7V or higher. VIN (Pin 3): Input Supply Pin. Must be locally bypassed with a good quality ceramic capacitor. Input supply must be 2.5V or higher. SW (Pins 4, 5): Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. Tie one side of the primary of the transformer to this pin. The target output voltage is set by the turns ratio of the transformer. Choose Turns Ratio N by the following equation: N= IGBTOUT (Pin 6): Output Drive for IGBT Gate. Connect this pin to the gate of the IGBT. IGBTIN (Pin 7): Logic Input Pin for IGBT Drive. When this pin is driven higher than 1.5V, the IGBT output pin goes high. When the pin is below 0.3V, the output is low. IGBTPWR (Pin 8): Input Supply Pin. Must be locally bypassed with a good quality ceramic capacitor. Input supply must be 0.1V higher than the turn-on voltage for the IGBT. DONE (Pin 9): Open NPN Collector Indication Pin. When target output voltage is reached, NPN turns on. This pin needs a pull-up resistor or current source. VMONT (Pin 10): Supplies a voltage proportional to the output voltage where 1V is the end of charge voltage. Only valid while the part is charging. Exposed Pad (Pin 11): Ground. Tie directly to local ground plane. VOUT + 2 31.5 where VOUT is the desired output voltage. 34850123fb 7 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 W FU CTIO AL BLOCK DIAGRA U PRIMARY C1 U TO VIN C2 DONE 10 3 2 R2 60k Q3 SAMPLE AND HOLD CHARGE VOUT SECONDARY SW 4, 5 VMONT 9 D1 T1 TO BATTERY Q Q S R CHIP POWER Q2 ENABLE R3 4k R1 2.5k R4 120k DCM COMPARATOR ONESHOT COUT PHOTOFLASH CAPACITOR + A3 – + – 1 ONESHOT 8 IGBT DRIVER POWER 45mV + A2 TO VIN IGBTIN VOUT COMPARATOR – 1.25V REFERENCE DRIVER 7 R IGBT DRIVER S Q Q1 20Ω + 20k ONESHOT RSENSE A1 – +– GND 11 20mV 6 3485 F01 TO GATE OF IGBT LT3485-3: RSENSE = 0.010Ω LT3485-0: RSENSE = 0.015Ω LT3485-2: RSENSE = 0.022Ω LT3485-1: RSENSE = 0.030Ω Figure 1 34850123fb 8 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U OPERATIO The LT3485-0/LT3485-1/LT3485-2/LT3485-3 are designed to charge photoflash capacitors quickly and efficiently. The operation of the part can be best understood by referring to Figure 1. When the CHARGE pin is first driven high, a one shot sets both SR latches in the correct state. The power NPN device, Q1, turns on and current begins ramping up in the primary of transformer T1. Comparator A1 monitors the switch current and when the peak current reaches 2A (LT3485-3), 1.4A (LT3485-0), 1A (LT3485-2) or 0.7A (LT3485-1), Q1 is turned off. Since T1 is utilized as a flyback transformer, the flyback pulse on the SW pin will cause the output of A3 to be high. The voltage on the SW pin needs to be at least 45mV higher than VBAT for this to happen. During this phase, current is delivered to the photoflash capacitor via the secondary and diode D1. As the secondary current decreases to zero, the SW pin voltage will begin to collapse. When the SW pin voltage drops to 45mV above VBAT or lower, the output of A3 (DCM Comparator) will go low. This fires a one shot which turns Q1 back on. This cycle will continue to deliver power to the output. Output voltage detection is accomplished via R2, R1, Q2, and comparator A2 (VOUT Comparator). Resistors R1 and R2 are sized so that when the SW voltage is 31.5V above VBAT, the output of A2 goes high which resets the master latch. This disables Q1 and halts power delivery. NPN transistor Q3 is turned on pulling the DONE pin low, indicating that the part has finished charging. Power delivery can only be restarted by toggling the CHARGE pin. The CHARGE pin gives full control of the part to the user. The charging can be halted at any time by bringing the CHARGE pin low. Only when the final output voltage is reached will the DONE pin go low. Figure 2 shows these various modes in action. When CHARGE is first brought high, charging commences. When CHARGE is brought low during charging, the part goes into shutdown and VOUT no longer rises. When CHARGE is brought high again, charging resumes. When the target VOUT voltage is reached, the DONE pin goes low and charging stops. Finally the CHARGE pin is brought low again so the part enters shutdown and the DONE pin goes high. Both VBAT and VIN have undervoltage lockout (UVLO). When one of these pins goes below its UVLO voltage, the DONE pin goes low. With an insufficient bypass capacitor on VBAT or VIN, the ripple on the pin is likely to activate UVLO and terminate the charge. The applications circuits in the data sheet suggest values adequate for most applications. The LT3485 VMONT pin functions as an output to a microcontroller to communicate the progress of the charge. The VMONT pin starts to function at about 0.2V, which corresponds to 64V with a turns ratio of 10.2. When the VMONT pin is at 1V, the DONE pin goes low and the charging terminates. The pin’s output is only valid when the part is charging. The LT3485 also integrates an IGBT drive. The IGBTPWR pin supplies the power. The IGBT output goes high when IGBTIN goes high and conversely goes low when IGBTIN goes low. While IGBTIN is low, the IGBT drive draws no quiescent current from IGBTPWR. VOUT 100V/DIV VDONE 5V/DIV VCHARGE 5V/DIV LT3485-2 VIN = 3.6V COUT = 50µF 1s/DIV 3485 F02 Figure 2. Halting the Charging Cycle with the CHARGE Pin 34850123fb 9 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W U U APPLICATIO S I FOR ATIO Choosing the Right Device (LT3485-0/LT3485-1/LT3485-2/LT3485-3) The only difference between the four versions of the LT3485 is the peak current level. For the fastest possible charge time, use the LT3485-3. The LT3485-1 has the lowest peak current capability, and is designed for applications that need a more limited drain on the batteries. Due to the lower peak current, the LT3485-1 can use a physically smaller transformer. The LT3485-0 and LT3485-2 have a current limit in between that of the LT3485-3 and the LT3485-1. Transformer Design The flyback transformer is a key element for any LT3485-0/LT3485-1/LT3485-2/LT3485-3 design. It must be designed carefully and checked that it does not cause excessive current or voltage on any pin of the part. The main parameters that need to be designed are shown in Table 1. The first transformer parameter that needs to be set is the turns ratio N. The LT3485-0/LT3485-1/LT3485-2/LT34853 accomplish output voltage detection by monitoring the flyback waveform on the SW pin. When the SW voltage reaches 31.5V higher than the VBAT voltage, the part will halt power delivery. Thus, the choice of N sets the target output voltage as it changes the amplitude of the reflected voltage from the output to the SW pin. Choose N according to the following equation: N= VOUT + 2 31.5 where VOUT is the desired output voltage. The number 2 in the numerator is used to include the effect of the voltage drop across the output diode(s). Thus for a 320V output, N should be 322/31.5 or 10.2. For a 300V output, choose N equal to 302/31.5 or 9.6. The next parameter that needs to be set is the primary inductance, LPRI. Choose LPRI according to the following formula: LPRI ≥ VOUT • 200 • 10 −9 N • IPK where VOUT is the desired output voltage. N is the transformer turns ratio. IPK is 1.4 (LT3485-0), 0.7 (LT3485-1), 1 (LT3485-2) and 2 (LT3485-3). LPRI needs to be equal or larger than this value to ensure that the LT3485-0/LT3485-1/LT3485-2/LT3485-3 has adequate time to respond to the flyback waveform. All other parameters need to meet or exceed the recommended limits as shown in Table 1. A particularly important parameter is the leakage inductance, LLEAK. When the power switch of the LT3485-0/LT3485-1/LT3485-2/ LT3485-3 turns off, the leakage inductance on the primary of the transformer causes a voltage spike to occur on the SW pin. The height of this spike must not exceed 40V, even though the absolute maximum rating of the SW Pin is 50V. The 50V absolute maximum rating is a DC blocking voltage specification, which assumes that the current in the power NPN is zero. Figure 3 shows the SW voltage waveform for the circuit of Figure 8 (LT3485-0). Table 1. Recommended Transformer Parameters PARAMETER LPRI LLEAK N VISO ISAT RPRI RSEC NAME Primary Inductance Primary Leakage Inductance Secondary: Primary Turns Ratio Secondary to Primary Isolation Voltage Primary Saturation Current Primary Winding Resistance Secondary Winding Resistance TYPICAL RANGE LT3485-0 >5 100 to 300 8 to 12 >500 >1.6 <300 <40 TYPICAL RANGE LT3485-1 >10 200 to 500 8 to 12 >500 >0.8 <500 <80 TYPICAL RANGE LT3485-2 >7 200 to 500 8 to 12 >500 >1.0 <400 <60 TYPICAL RANGE LT3485-3 >3.5 100 to 300 8 to 12 >500 >2 <200 <30 UNITS µH nH V A mΩ Ω 34850123fb 10 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U W U U APPLICATIO S I FOR ATIO Note that the absolute maximum rating of the SW pin is not exceeded. Make sure to check the SW voltage waveform with VOUT near the target output voltage, as this is the worst case condition for SW voltage. Figure 4 shows the various limits on the SW voltage during switch turn off. Capacitor Selection It is important not to minimize the leakage inductance to a very low level. Although this would result in a very low leakage spike on the SW pin, the parasitic capacitance of the transformer would become large. This will adversely affect the charge time of the photoflash circuit. Output Diode Selection Linear Technology has worked with several leading magnetic component manufacturers to produce pre-designed flyback transformers for use with the LT3485-0/LT34851/LT3485-2/LT3485-3. Table 2 shows the details of several of these transformers. For the input bypass capacitors, high quality X5R or X7R types should be used. Make sure the voltage capability of the part is adequate. The rectifying diode(s) should be low capacitance type with sufficient reverse voltage and forward current ratings. The peak reverse voltage that the diode(s) will see is approximately: VPK − R = VOUT + (N • VIN ) “B” IPRI 1A/DIV 2 “A” MUST BE LESS THAN 40V VSW VSW 10A/DIV MUST BE LESS THAN 50V 0V VIN = 5V VOUT = 320V 100ns/DIV 3485 F03 3485 F04 Figure 4. New Transformer Design Check (Not to Scale) Figure 3. LT3485 SW Voltage Waveform Table 2. Pre-Designed Transformers – Typical Specifications Unless Otherwise Noted TRANSFORMER NAME SBL-5.6-1 SBL-5.6S-1 SIZE (W × L × H) mm 5.6 × 8.5 × 4.0 5.6 × 8.5 × 3.0 LPRI (µH) 10 24 LPRI-LEAKAGE FOR USE WITH LT3485-0/LT3485-2 LT3485-1 (nH) 200 Max 400 Max N 10.2 10.2 RPRI (mΩ) 103 305 RSEC (Ω) 26 55 LT3485-0 LT3485-1 LT3485-2 LT3485-3 LT3485-0/LT3485-1 LT3485-1 LT3485-3 LDT565630T-001 LDT565630T-002 LDT565630T-003 LDT565630T-041 T-15-089 T-15-083 T-17-109A 5.8 × 5.8 × 3.0 5.8 × 5.8 × 3.0 5.8 × 5.8 × 3.0 5.8 × 5.8 × 3.0 6.4 × 7.7 × 4.0 8.0 × 8.9 × 2.0 6.5 × 7.9 × 4.0 6 14.5 10.5 4.7 12 20 5.9 200 Max 500 Max 550 Max 150 Max 400 Max 500 Max 300 Max 10.4 10.2 10.2 10.4 10.2 10.2 10.2 100 Max 240 Max 210 Max 90 Max 211 Max 675 Max 78 Max 10 Max 16.5 Max 14 Max 6.4 Max 27 Max 35 Max 18.61 Max VENDOR Kijima Musen Hong Kong Office 852-2489-8266 (ph) [email protected] (email) TDK Chicago Sales Office (847) 803-6100 (ph) www.components.tdk.com Tokyo Coil Engineering Japan Office 0426-56-6262 (ph) www.tokyo-coil.co.jp 34850123fb 11 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U U W U APPLICATIO S I FOR ATIO The peak current of the diode is simply: IGBT Drive 2 IPK-SEC = (LT3485-3) N 1.4 IPK-SEC = (LT3485-0) N 1 IPK-SEC = (LT3485-2) N 0.7 IPK-SEC = (LT3485-1) N For the circuit of Figure 8 with VBAT of 5V, VPK-R is 371V and IPK-SEC is 137mA. The GSD2004S dual silicon diode is recommended for most LT3485-0/LT3485-1/LT34852/LT3485-3 applications. Another option is to use the BAV23S dual silicon diodes. Table 3 shows the various diodes and relevant specifications. Use the appropriate number of diodes to achieve the necessary reverse breakdown voltage. The IGBT is a high current switch for the 100A+ current through the photoflash lamp. To create a redeye effect or to adjust the light output, the lamp current needs to be stopped, or quenched, with an IGBT before discharging the photoflash capacitor fully. The IGBT device also controls the 4kV trigger pulse required to ionize the xenon gas in the photoflash lamp. Figure 5 is a schematic of a fully functional photoflash application with the LT3485 serving as the IGBT drive. An IGBT drive charges the gate capacitance to start the flash. The IGBT drive does not need to pull-up the gate fast because of the inherently slow nature of the IGBT. A rise time of 2µs is sufficient to charge the gate of the IGBT and create a trigger pulse. With slower rise times, the trigger circuitry will not have a fast enough edge to create the required 4kV pulse. The fall time of the IGBT drive is critical to the safe operation of the IGBT. The IGBT gate is a network of resistors and capacitors, as shown in Figure 6. When the gate terminal is pulled low, Table 3. Recommended Output Diodes MAX REVERSE VOLTAGE (V) 2x300 MAX FORWARD CONTINUOUS CURRENT (mA) 225 CAPACITANCE (pF) 5 BAV23S (Dual Diode) 2x250 225 5 MMBD3004S (Dual Diode) 2x350 225 5 PART GSD2004S (Dual Diode) VBAT 2 AA OR 1 TO 2 Li-Ion 320V 1:10.2 1 • 4 4.7µF 2 • 1M 5 150µF PHOTOFLASH CAPACITOR SW VBAT DONE GND 2 LT3485-0 VIN 0.22µF VMONT IGBTPWR IGBTIN A 2.2µF 600V TRIGGER T 1 CHARGE VCC 5V VENDOR Vishay (402) 563-6866 www.vishay.com Philips Semiconductor (800) 234-7381 www.philips.com Diodes Inc (816) 251-8800 www.diodes.com FLASHLAMP 3 TO MICRO C IGBT IGBTOUT 3485 F05 Figure 5. Complete Xenon Circuit 34850123fb 12 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U U W U APPLICATIO S I FOR ATIO rise time is 270ns. The drive pulls high to IGBTPWR. The typical 90% to 10% fall time is 180ns. The drive pulls down to 300mV. The IGBT driver pulls a peak of 150mA when driving an IGBT and 2mA of quiescent current. In the low state, the IGBT’s quiescent current is less than 0.1µA. GATE 3485 F06 EMITTER Figure 6. IGBT Gate the capacitance closest to the terminal goes low but the capacitance further from the terminal remains high. This causes a small portion of the device to handle the full 100A of current, which quickly destroys the device. The pull down circuitry needs to pull down slower than the internal RC time constant in the gate of the IGBT. This is easily accomplished with a resistor in series with the IGBT drive, which is integrated into the LT3485. The LT3485’s integrated drive circuit is independent of the charging function. The IGBT section draws its power from the IGBTPWR pin. The rise and fall times are measured using a 4000pF output capacitor. The typical 10% to 90% Table 4 is a list of recommended IGBT devices for strobe applications. These three devices are all packaged in 8-lead TSSOP packages. VOUT Monitor The voltage output monitor is a new feature to monitor the progress of capacitor charging with a microcontroller. The monitor uses the flyback waveform to output a voltage proportional to the output of the flyback converter. The output monitor voltage range for the pin is 0V to 1V. The 1V output corresponds with the charge cycle terminating and the DONE pin going low. The voltage output monitor is only functional when the circuit is charging (DONE and CHARGE are high.) Table 4. Recommended IGBTs PART CY25BAH-8F CY25BAJ-8F GT8G133 DRIVE VOLTAGE (V) 2.5 4 BREAKDOWN VOLTAGE (V) 400 400 COLLECTOR CURRENT (PULSED) (A) 150 150 4 400 150 VENDOR Renesas (408) 382-7500 www.renesas.com Toshiba Semiconductor (949) 623-2900 www.semicon.toshiba.co.jp/eng/ 34850123fb 13 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U U W U APPLICATIO S I FOR ATIO Board Layout The high voltage operation of the LT3485-0/LT3485-1/ LT3485-2/LT3485-3 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 7 shows the recommended component placement. Keep the area for the high voltage end of the secondary as small as possible. Also note the larger than minimum spacing for all high voltage nodes in order to meet breakdown voltage requirements for the circuit board. It is imperative to keep the electrical path formed by C1, the primary of T1, and the LT3485-0/LT3485-1/ LT3485-2/LT3485-3 as short as possible. If this path is haphazardly made long, it will effectively increase the leakage inductance of T1, which may result in an overvoltage condition on the SW pin. VMONT CHARGE R1 DONE C2 10 2 9 C3 8 IGBTPWR 4 7 IGBTIN 5 6 3 + COUT PHOTOFLASH CAPACITOR VIN 1 11 IGBTOUT • T1 SECONDARY 3485 F07 PRIMARY • C1 D1 (DUAL DIODE) VBAT Figure 7. Suggested Layout: Keep Electrical Path Formed by C1, Transformer Primary and LT3485-0/LT3485-1/LT3485-2/LT3485-3 Short 34850123fb 14 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U TYPICAL APPLICATIO S VBAT 1.8V TO 8V T1 1:10.2 D1 320V C1 4.7µF R1 100k COUT PHOTOFLASH CAPACITOR SW VBAT DONE DONE GND CHARGE CHARGE LT3485-0 VIN 2.5V TO 8V VIN C2 0.22µF VMONT IGBTPWR TO MICRO IGBTOUT TO GATE OF IGBT IGBTIN 3485 F08 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 8. LT3485-0 Photoflash Charger Uses High Efficiency 4mm Tall Transformer VBAT 1.8V TO 8V T1 1:10.2 DONE 320V C1 4.7µF R1 100k CHARGE D1 COUT PHOTOFLASH CAPACITOR SW VBAT DONE GND CHARGE LT3485-1 VIN 2.5V TO 8V C2 0.22µF VIN IGBTPWR IGBTIN VMONT TO MICRO IGBTOUT TO GATE OF IGBT 3485 F09 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6S-1, LPRI = 24µH, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 9. LT3485-1 Photoflash Charger Uses High Efficiency 3mm Tall Transformer 34850123fb 15 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U TYPICAL APPLICATIO S VBAT 1.8V TO 8V T1 1:10.2 D1 320V C1 4.7µF R1 100k COUT PHOTOFLASH CAPACITOR SW VBAT DONE DONE GND CHARGE CHARGE LT3485-2 VIN 2.5V TO 8V VIN C2 0.22µF VMONT IGBTPWR TO MICRO IGBTOUT TO GATE OF IGBT IGBTIN 3485 F10 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 10. LT3485-2 Photoflash Charger Uses High Efficiency 4mm Tall Transformer VBAT 1.8V TO 8V T1 1:10.2 DONE 320V C1 4.7µF R1 100k CHARGE D1 COUT PHOTOFLASH CAPACITOR SW VBAT DONE GND CHARGE LT3485-3 VIN 2.5V TO 8V VIN C2 0.22µF VMONT IGBTPWR TO MICRO IGBTOUT IGBTIN TO GATE OF IGBT 3485 F11 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: TDK LDT565630T-041, LPRI = 4.7µH, N = 10.4 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 11. LT3485-3 Photoflash Charger Uses High Efficiency 3mm Tall Transformer 34850123fb 16 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U TYPICAL APPLICATIO S T1 1:10.2 VBAT 1.8V TO 8V D1 320V C1 4.7µF COUT PHOTOFLASH CAPACITOR SW VBAT DONE DONE GND CHARGE CHARGE LT3485-0 VIN 2.5V TO 8V VIN C2 0.22µF VMONT IGBTPWR TO MICRO IGBTOUT TO GATE OF IGBT IGBTIN 3485 F12 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: TDK LDT565630T-001, LPRI = 6µH, N = 10.4 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 12. LT3485-0 Photoflash Circuit Uses Tiny 3mm Tall Transformer 6 COUT = 50µF CHARGE TIME (SECONDS) 5 LT3485-1 4 LT3485-2 3 2 1 LT3485-0 0 2 3 LT3485-3 4 5 VIN (V) 6 7 8 3485 F13 Figure 13. Charge Time with TDK Transformers (Figures 11, 12, 13, 14 and 15) 34850123fb 17 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U TYPICAL APPLICATIO S VBAT 1.8V TO 8V T1 1:10.2 D1 320V C1 4.7µF COUT PHOTOFLASH CAPACITOR SW VBAT DONE DONE GND CHARGE CHARGE LT3485-1 VIN 2.5V TO 8V VIN C2 0.22µF VMONT IGBTPWR TO MICRO IGBTOUT TO GATE OF IGBT IGBTIN 3485 F14 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: TDK LDT565630T-002, LPRI = 14.5µH, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 14. LT3485-1 Photoflash Circuit Uses Tiny 3mm Tall Transformer VBAT 1.8V TO 8V T1 1:10.2 CHARGE 320V C1 4.7µF COUT PHOTOFLASH CAPACITOR SW VBAT DONE D1 DONE GND CHARGE LT3485-2 VIN 2.5V TO 8V VIN C2 0.22µF IGBTPWR IGBTIN VMONT TO MICRO IGBTOUT TO GATE OF IGBT 3485 F15 C1: 4.7µF, X5R OR X7R, 10V C2: 0.22µF, X5R or X7R, 10V T1: TDK LDT565630T-003, LPRI = 10µH, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 15. LT3485-2 Photoflash Circuit Uses Tiny 3mm Tall Transformer 34850123fb 18 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 6 3.00 ±0.10 (4 SIDES) 0.38 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1005 5 0.200 REF 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 34850123fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LT3485-0/LT3485-1/ LT3485-2/LT3485-3 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3407 Dual 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40µA, ISD <1µA, MS10E LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Chargers with Automatic Top-Off Charges 220µF to 320V in 3.7 seconds from 5V, VIN: 2.2V to 16V, IQ = 90µA, ISD < 1µA, MS10 LTC3425 5A ISW, 8MHz, Multi-Phase Synchronous Step-Up DC/DC Converter 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MIN) = 5.25V, IQ = 12µA, ISD < 1µA, QFN-32 LTC3440 600mA/1A (IOUT), Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V to 5.5V, IQ = 25µA, ISD < 1µA, MS-10 DFN-12 LT3468/LT3468-1/ LT3468-2 Photoflash Capacitors in ThinSOT™ Charges 110µF to 320V in 4.6 Seconds from 3.6V, VIN: 2.5V to 16V, IQ = 5mA, ISD < 1µA, ThinSOT LT3472 Dual ±34V, 1.2MHz Boost (350mA)/Inverting (400mA) DC/DC Converter for CCD Bias Integrated Schottkys, VIN: 2.2V to 16V, VOUT(MAX) = ±34V, IQ = 2.5mA, ISD < 1µA, DFN LT3463/LT3463A Dual Boost (250mA)/Inverting (250mA/400mA) DC/DC Converter for CCD Bias Integrated Schottkys, VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40µA, ISD < 1µA, DFN LT3484-0/LT3484-1/ LT3484-2 Photoflash Capacitor Chargers Charges 110µF to 320V in 4.6 Seconds from 3.6V, VIN: 2.5V to 16V, VBAT: 1.8V to 16V, IQ = 5mA, ISD < 1µA, 2mm × 3mm DFN ThinSOT is a trademark of Linear Technology Corporation. 34850123fb 20 Linear Technology Corporation LT 0406 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005