LT3468/LT3468-1/LT3468-2 Photoflash Capacitor Chargers in ThinSOT TM U FEATURES DESCRIPTIO ■ The LT®3468/LT3468-1/LT3468-2 are highly integrated ICs designed to charge photoflash capacitors in digital and film cameras. A patented control technique* allows for the use of extremely small transformers. Each device contains an on-chip high voltage NPN power switch. Output voltage detection* is completely contained within the device, eliminating the need for any discrete zener diodes or resistors. The output voltage can be adjusted by simply changing the turns ratio of the transformer. The LT3468 has a primary current limit of 1.4A, the LT3468-2 has a 1A limit, and the LT3468-1 has a 0.7A limit. These different current limit levels result in well controlled input currents of 500mA for the LT3468, 375mA for the LT3468-2 and 225mA for the LT3468-1. Aside from the differing current limit, the three devices are otherwise equivalent. ■ ■ ■ ■ ■ ■ ■ ■ Highly Integrated IC Reduces Solution Size Uses Small Transformers: 5.8mm × 5.8mm × 3mm Fast Photoflash Charge Times: 4.6s for LT3468 (0V to 320V, 100µF, VIN = 3.6V) 5.7s for LT3468-2 (0V to 320V, 100µF, VIN = 3.6V) 5.5s for LT3468-1 (0V to 320V, 50µF, VIN = 3.6V) Controlled Input Current: 500mA (LT3468) 375mA (LT3468-2) 225mA (LT3468-1) Supports Operation from Single Li-Ion Cell, or Any Supply from 2.5V up to 16V Adjustable Output Voltage No Output Voltage Divider Needed Charges Any Size Photoflash Capacitor Low Profile (<1mm) SOT-23 Package U APPLICATIO S ■ ■ Digital / Film Camera Flash PDA / Cell Phone Flash Emergency Strobe , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. *Protected by U.S. Patents, including 6518733. U ■ 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 LT3468 series of parts are available in tiny low profile (1mm) SOT-23 packages. TYPICAL APPLICATIO LT3468 Photoflash Charger Uses High Efficiency 4mm Tall Transformer LT3468 Charging Waveform DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VIN = 3.6V COUT = 100µF 1:10.2 VIN 2.5V TO 8V 1 4 2 5 320V 4.7µF + 100µF 100k SW VIN AVERAGE INPUT CURRENT 1A/DIV LT3468 DONE CHARGE DONE VOUT 50V/DIV GND 1s/DIV 3468 G01 CHARGE 346812 TA01 346812fa 1 LT3468/LT3468-1/LT3468-2 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER VIN Voltage .............................................................. 16V SW Voltage ................................................ –0.4V to 50V CHARGE Voltage ...................................................... 10V DONE Voltage .......................................................... 10V Current into DONE Pin .......................................... ±1mA Maximum Junction Temperature .......................... 125°C Operating Temperature Range (Note 2) ...–40°C to 85°C Storage Temperature Range ..................–65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C TOP VIEW SW 1 LT3468ES5 LT3468ES5-1 LT3468ES5-2 5 VIN GND 2 DONE 3 4 CHARGE S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC TSOT-23 TJMAX = 125°C θJA = 150°C ON BOARD OVER GROUND PLANE θJC = 90°C/W LTAEC LTAGQ LTBCH 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 = 3V, VCHARGE = VIN unless otherwise noted. (Note 2) Specifications are for the LT3468, LT3468-1 and LT3468-2 unless otherwise noted. PARAMETER CONDITIONS Quiescent Current Not Switching VCHARGE = 0V MIN ● Input Voltage Range Switch Current Limit LT3468 (Note 3) LT3468-2 LT3468-1 Switch VCESAT LT3468, ISW = 1A LT3468-2, ISW = 650mA LT3468-1, ISW = 400mA VOUT Comparator Trip Voltage Measured as VSW – VIN VOUT Comparator Overdrive 300ns Pulse Width DCM Comparator Trip Voltage Measured as VSW – VIN CHARGE Pin Current VCHARGE = 3V VCHARGE = 0V Switch Leakage Current VIN = VSW = 5V, in Shutdown MAX 5 0 8 1 mA µA 16 V 1.2 0.87 0.55 1.3 0.97 0.65 A A A 330 210 150 430 280 200 mV mV mV 31.5 32 V 200 400 mV 36 80 mV 15 0 40 0.1 µA µA 0.01 1 µA 2.5 1.1 0.77 0.45 ● 31 ● 10 ● ● CHARGE Input Voltage High TYP 1 V ● CHARGE Input Voltage Low UNITS 0.3 V Minimum Charge Pin Low Time High→Low→High 20 µs DONE Output Signal High 100kΩ from VIN to DONE 3 V DONE Output Signal Low 33µA into DONE Pin 100 200 mV DONE Leakage Current VDONE = 3V, DONE NPN Off 20 100 nA Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT3468E/LT3468E-1/LT3468E-2 are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process. Note 3: Specifications are for static test. Current limit in actual application will be slightly higher. 346812fa 2 LT3468/LT3468-1/LT3468-2 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3468 curves use the circuit of Figure 6, LT3468-1 curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted. LT3468 Charging Waveform LT3468-1 Charging Waveform VIN = 3.6V COUT = 100µF VIN = 3.6V COUT = 50µF LT3468-2 Charging Waveform VIN = 3.6V COUT = 100µF VOUT 50V/DIV VOUT 50V/DIV VOUT 50V/DIV AVERAGE INPUT CURRENT 1A/DIV AVERAGE INPUT CURRENT 0.5A/DIV 1s/DIV 3468 G01 10 TA = 25°C LT3468-2 Charge Time TA = 25°C 9 8 8 8 7 7 7 5 COUT = 100µF 4 3 2 CHARGE TIME (s) 9 6 6 5 COUT = 50µF 4 3 2 COUT = 50µF 1 0 3 4 5 6 VIN (V) 7 8 9 3 4 5 6 VIN (V) 7 8 VIN = 2.8V VIN = 4.2V VIN = 3.6V 200 0 100 150 200 VOUT (V) 250 300 3468 G07 3 6 5 VIN (V) 4 7 LT3468-2 Input Current TA = 25°C 300 VIN = 2.8V 200 VIN = 4.2V VIN = 3.6V 100 9 8 3468 G06 600 0 50 COUT = 50µF 2 9 AVERAGE INPUT CURRENT (mA) AVERAGE INPUT CURRENT (mA) AVERAGE INPUT CURRENT (mA) TA = 25°C 0 3 LT3468-1 Input Current 400 600 COUT = 100µF 4 3468 G05 LT3468 Input Current 400 5 0 2 3468 G04 800 6 1 0 2 TA = 25°C 2 COUT = 20µF 1 3468 G03 1s/DIV 10 9 CHARGE TIME (s) CHARGE TIME (s) 3468 G02 LT3468-1 Charge Time LT3468 Charge Time 10 1s/DIV AVERAGE INPUT CURRENT 0.5A/DIV TA = 25°C 450 VIN = 2.8V 300 VIN = 4.2V VIN = 3.6V 150 0 0 50 100 150 200 VOUT (V) 250 300 3468 G08 0 50 100 150 200 VOUT (V) 250 300 3468 G09 346812fa 3 LT3468/LT3468-1/LT3468-2 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3468 curves use the circuit of Figure 6, LT3468-1 curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted. LT3468 Efficiency 90 90 TA = 25°C 90 TA = 25°C 80 80 EFFICIENCY (%) VIN = 2.8V VIN = 3.6V 60 50 VIN = 2.8V 70 EFFICIENCY (%) 80 70 VIN = 3.6V 60 50 40 100 150 200 VOUT (V) 250 300 LT3468 Output Voltage 60 100 150 200 VOUT (V) 250 TA = –40°C 319 323 318 TA = 25°C TA = 25°C 321 TA = 85°C TA = 85°C 316 315 320 TA = –40°C 314 319 319 318 313 318 3 4 5 VIN (V) 6 7 8 312 2 3 4 5 VIN (V) 6 3468 G13 8 2 0.700 4 5 VIN (V) 6 ILIM (A) 7 8 LT3468-2 Switch Current Limit 1.00 VIN = 3V VOUT = 0V VIN = 3V VOUT = 0V 0.660 0.96 0.620 0.92 ILIM (A) VIN = 3V VOUT = 0V 1.3 3 3468 G15 LT3468-1 Switch Current Limit 1.4 ILIM (A) 7 3468 G14 LT3468 Switch Current Limit 1.5 300 317 VOUT (V) VOUT (V) 320 2 250 LT3468-2 Output Voltage 324 TA = –40°C TA = 85°C 200 150 VOUT (V) 3468 G12 322 TA = 25°C 100 50 300 LT3468-1 Output Voltage 322 VOUT (V) VIN = 3.6V 3468 G11 324 321 VIN = 2.8V 70 40 50 3468 G10 323 VIN = 4.2V 50 40 50 TA = 25°C VIN = 4.2V VIN = 4.2V EFFICIENCY (%) LT3468-2 Efficiency LT3468-1 Efficiency 0.580 0.88 0.540 0.84 1.2 1.1 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 3468 G16 0.500 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 3468 G17 0.80 –40 –20 40 20 0 60 TEMPERATURE (°C) 80 100 34682 G18 346812fa 4 LT3468/LT3468-1/LT3468-2 U W TYPICAL PERFOR A CE CHARACTERISTICS LT3468 curves use the circuit of Figure 6, LT3468-1 curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted. LT3468 Switching Waveform LT3468-2 Switching Waveform LT3468-1 Switching Waveform VIN = 3.6V VOUT = 100V VIN = 3.6V VOUT = 100V VIN = 3.6V VOUT = 100V VSW 10V/DIV IPRI 1A/DIV 1µs/DIV VSW 10V/DIV VSW 10V/DIV IPRI 1A/DIV IPRI 1A/DIV 1µs/DIV 3468 G19 VIN = 3.6V VOUT = 300V VIN = 3.6V VOUT = 300V VIN = 3.6V VOUT = 300V VSW 10V/DIV IPRI 1A/DIV VSW 10V/DIV VSW 10V/DIV IPRI 1A/DIV IPRI 1A/DIV 1µs/DIV 1µs/DIV 3468 G20 3468 G21 LT3468-2 Switching Waveform LT3468-1 Switching Waveform LT3468 Switching Waveform 3468 G24 3468 G23 LT3468/LT3468-1/LT3468-2 Switch Breakdown Voltage 10 SWITCH CURRENT (mA) 1µs/DIV 1µs/DIV 3468 G22 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) 3468 G25 346812fa 5 LT3468/LT3468-1/LT3468-2 U U U PI FU CTIO S SW (Pin 1): 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= VOUT + 2 31.5 Where: VOUT is the desired output voltage. You must tie a Schottky diode from GND to SW, with the anode at GND for proper operation of the circuit. Please refer to the applications section for further information. DONE (Pin 3): Open NPN Collector Indication Pin. When target output voltage is reached, NPN turns on. This pin needs a pull-up resistor or current source. CHARGE (Pin 4): Charge Pin. This pin must be brought high (>1V) to enable the part. A low (<0.3V) to high (>1V) transition on this pin puts the part into power delivery mode. Once the target output voltage is reached, the part will stop charging the output. Toggle this pin to start charging again. Ground to shut down. You may bring this pin low during a charge cycle to halt charging at any time. VIN (Pin 5): Input Supply Pin. Must be locally bypassed with a good quality ceramic capacitor. Input supply must be 2.5V or higher. GND (Pin 2): Ground. Tie directly to local ground plane. W BLOCK DIAGRA D1 T1 TO BATTERY VOUT PRIMARY C1 SECONDARY D2 3 DONE 5 VIN + SW 1 R2 60k Q3 COUT PHOTOFLASH CAPACITOR DCM COMPARATOR + ONESHOT A3 – + – 36mV Q2 Q1 ENABLE MASTER LATCH Q S R1 2.5k Q R DRIVER R S Q1 Q + A2 – + 1.25V REFERENCE A1 VOUT COMPARATOR CHARGE 4 20mV – ONESHOT RSENSE +– 2 GND CHIP ENABLE LT3468: RSENSE = 0.015Ω LT3468-2: RSENSE = 0.022Ω LT3468-1: RSENSE = 0.03Ω 3486 BD Figure 1 346812fa 6 LT3468/LT3468-1/LT3468-2 U OPERATIO The LT3468/LT3468-1/LT3468-2 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 1.4A (LT3468), 1A(LT3468-2) or 0.7A (LT3468-1), 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 36mV higher than VIN 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 36mV above VIN 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 VIN, 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. LT3468-2 VIN = 3.6V VOUT COUT = 50µF 100V/DIV VDONE 5V/DIV VCHARGE 5V/DIV 1s/DIV 3468 F02 Figure 2. Halting the Charging Cycle with the CHARGE Pin U W U U APPLICATIO S I FOR ATIO Choosing The Right Device (LT3468/LT3468-1/ LT3468-2) The only difference between the three versions of the LT3468 is the peak current level. For the fastest possible charge time, use the LT3468. The LT3468-1 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 LT3468-1 can use a physically smaller transformer. The LT3468-2 has a current limit in between that of the LT3468 and the LT3468-1. Transformer Design The flyback transformer is a key element for any LT3468/ LT3468-1/LT3468-2 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 LT3468/LT3468-1/LT3468-2 accomplish output voltage detection by monitoring the flyback waveform on the SW pin. When the SW voltage reaches 31.5V higher than the VIN 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 346812fa 7 LT3468/LT3468-1/LT3468-2 U W U U APPLICATIO S I FOR ATIO 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: VOUT • 200 • 10 −9 N • IPK Where: V OUT is the desired output voltage. N is the transformer turns ratio. IPK is 1.4 (LT3468), 0.7 (LT3468-1), and 1.0 (LT3468-2). LPRI ≥ LPRI needs to be equal or larger than this value to ensure that the LT3468/LT3468-1/LT3468-2 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 LT3468/LT3468-1/LT3468-2 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 6(LT3468). 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. 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 effect the charge time of the photoflash circuit. Linear Technology has worked with several leading magnetic component manufacturers to produce pre-designed flyback transformers for use with the LT3468/LT3468-1/ LT3468-2. Table 2 shows the details of several of these transformers. Table 1. Recommended Transformer Parameters TYPICAL RANGE LT3468 PARAMETER NAME LPRI Primary Inductance LLEAK Primary Leakage Inductance N Secondary: Primary Turns Ratio VISO ISAT TYPICAL RANGE LT3468-1 TYPICAL RANGE LT3468-2 UNITS >5 >10 >7 µH 100 to 300 200 to 500 200 to 500 nH 8 to 12 8 to 12 8 to 12 Secondary to Primary Isolation Voltage >500 >500 >500 V Primary Saturation Current >1.6 >0.8 >1.0 A RPRI Primary Winding Resistance <300 <500 <400 mΩ RSEC Secondary Winding Resistance <40 <80 <60 Ω VIN = 5V VOUT = 320V “B” “A” VSW MUST BE LESS THAN 50V MUST BE LESS THAN 40V VSW 10V/DIV 0V 3420 F07 100ns/DIV 3468 G18 Figure 3. LT3468 SW Voltage Waveform Figure 4. New Transformer Design Check (Not to Scale). 346812fa 8 LT3468/LT3468-1/LT3468-2 U W U U APPLICATIO S I FOR ATIO Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted. FOR USE WITH LT3468/LT3468-2 LT3468-1 LT3468 LT3468-1 LT3468-2 SIZE (W × L × H) mm LPRI (µH) LPRI-LEAKAGE TRANSFORMER NAME (nH) N RPRI (mΩ) RSEC (Ω) SBL-5.6-1 SBL-5.6S-1 5.6 × 8.5 × 4.0 5.6 × 8.5 × 3.0 10 24 200 Max 400 Max 10.2 10.2 103 305 26 55 LDT565630T-001 LDT565630T-002 LDT565630T-003 5.8 × 5.8 × 3.0 5.8 × 5.8 × 3.0 5.8 × 5.8 × 3.0 6 14.5 10.5 200 Max 500 Max 550 Max 10.4 10.2 10.2 100 Max 10 Max 240 Max 16.5 Max 210 Max 14 Max TDK Chicago Sales Office (847) 803-6100 (ph) www.components.tdk.com T-15-089 T-15-083 6.4 × 7.7 × 4.0 8.0 × 8.9 × 2.0 12 20 400 Max 500 Max 10.2 10.2 211 Max 27 Max 675 Max 35 Max Tokyo Coil Engineering Japan Office 0426-56-6262 (ph) www.tokyo-coil.co.jp LT3468/LT3468-1 LT3468-1 Capacitor Selection For the input bypass capacitor, a high quality X5R or X7R type should be used. Make sure the voltage capability of the part is adequate. Output Diode Selection 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 ) 1.4 (LT3468) N IPK −SEC = 1.0 (LT3468-2) N 0.7 (LT3468-1) N For the circuit of Figure 6 with VIN of 5V, VPK-R is 371V and IPK-SEC is 137mA. The GSD2004S dual silicon diode is recommended for most LT3468/LT3468-1/LT3468-2 applications. Another option is to use the BAV23S dual silicon diodes. Diodes Incorporated makes a dual diode named MMBD3004S which also meets all the requirements. Table 3 shows the various diodes and relevant specifications. Use the appropriate number of diodes to achieve the necessary reverse breakdown voltage. IPK −SEC = SW Pin Clamp Diode Selection The peak current of the diode is simply: IPK −SEC = VENDOR Kijima Musen Hong Kong Office 852-2489-8266 (ph) [email protected] (email) The diode D2 in Figure 6 is needed to clamp the SW node. Due to the new control scheme of the LT3468/LT3468-1/ LT3468-2, the SW node may go below ground during a switch cycle. The clamp diode prevents the SW node from going too far below ground. The diode is required for proper operation of the circuit. The recommended diode Table 3. Recommended Output Diodes MAX REVERSE VOLTAGE (V) MAX FORWARD CONTINUOUS CURRENT (mA) CAPACITANCE (pF) GSD2004S (Dual Diode) 2x300 225 5 Vishay (402) 563-6866 www.vishay.com BAV23S (Dual Diode) 2x250 225 5 Philips Semiconductor (800) 234-7381 www.philips.com MMBD3004S 2x350 225 5 Diodes Incorporated (805) 446-4800 www.diodes.com PART VENDOR 346812fa 9 LT3468/LT3468-1/LT3468-2 U U W U APPLICATIO S I FOR ATIO MAX REVERSE VOLTAGE (V) PART ZHCS400 VENDOR 40 B0540W Zetex (631) 360-2222 www.zetex.com 40 MA2Z720 Diodes Inc. (805) 446-4800 www.diodes.com 40 VIN C1 R1 D1 (DUAL DIODE) DONE CHARGE 4 3 • 2 Panasonic (408) 487-9510 www.panasonic.co.jp 5 T1 SECONDARY Table 4. Recommended Clamp Diodes 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 LT3468/LT3468-1/LT3468-2 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. PRIMARY should be a Schottky diode with at least a 500mA peak forward current capability. The diode forward voltage drop should be 600mV or less at 500mA of forward current. Reverse voltage rating should be 40V or higher. Table 4 shows various recommended clamping diodes. • COUT PHOTOFLASH CAPACITOR + 1 D2 Board Layout 3468 F05 The high voltage operation of the LT3468/LT3468-1/ LT3468-2 demands careful attention to board layout. You will not get advertised performance with careless layout. Figure 5 shows the recommended component placement. Figure 5. Suggested Layout: Keep Electrical Path Formed by C1, Transformer Primary and LT3468/LT3468-1/LT3468-2 Short U TYPICAL APPLICATIO S T1 1:10.2 VIN 2.5V TO 8V C1 4.7µF D1 1 4 2 5 320V + R1 100k DONE CHARGE SW VIN COUT PHOTOFLASH CAPACITOR D2 LT3468 DONE T1 1:10.2 VIN 2.5V TO 8V C1 4.7µF R1 100k CHARGE CHARGE 4 5 3 6 320V + DONE GND D1 VIN SW COUT PHOTOFLASH CAPACITOR D2 LT3468-1 GND DONE CHARGE 3468 F06 C1: 4.7µF, X5R OR X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2 D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED Figure 6. LT3468 Photoflash Charger Uses High Efficiency 4mm Tall Transformer C1: 4.7µF, X5R OR X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6S-1, LPRI = 24µH, N = 10.2 D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED 3468 F07 Figure 7. LT3468-1 Photoflash Charger Uses High Efficiency 3mm Tall Transformer 346812fa 10 LT3468/LT3468-1/LT3468-2 U TYPICAL APPLICATIO S T1 1:10.2 VIN 2.5V TO 8V C1 4.7µF D1 5 4 8 1 320V + SW VIN R1 100k COUT PHOTOFLASH CAPACITOR D2 LT3468-2 GND DONE DONE CHARGE CHARGE C1: 4.7µF, X5R OR X7R, 10V T1: TDK LDT565630T-003 LPRI = 10.5µH, N = 10.2 D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED 3468 F08 Figure 8. LT3468-2 Photoflash Charger Uses High Efficiency 3mm Tall Transformer U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 1.90 BSC S5 TSOT-23 0302 346812fa 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. 11 LT3468/LT3468-1/LT3468-2 U TYPICAL APPLICATIO S LT3468 Photoflash Circuit uses Tiny 3mm Tall Transformer T1 1:10.4 C1 4.7µF Charge Time D1 5, 6 4 7, 8 1 9 8 + R1 100k 3 DONE 4 CHARGE 5 1 VIN SW COUT PHOTOFLASH CAPACITOR D2 LT3468 2 GND DONE 10 320V CHARGE TIME (s) VIN 2.5V TO 8V CHARGE 7 6 5 4 COUT = 100µF 3 2 COUT = 50µF 1 C1: 4.7µF, X5R OR X7R, 10V T1: TDK PART# LDT565630T-001, LPRI = 6µH, N = 10.4 D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED 0 2 3 4 5 6 VIN (V) 3468 TA03 7 8 9 3468 TA05 LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer T1 1:10.2 C1 4.7µF Charge Time D1 5 4 8 1 9 + R1 100k DONE CHARGE 3 4 10 320V 5 1 VIN SW 8 COUT PHOTOFLASH CAPACITOR D2 LT3468-1 2 GND DONE CHARGE CHARGE TIME (s) VIN 2.5V TO 8V 7 6 5 4 COUT = 50µF 3 2 C1: 4.7µF, X5R OR X7R, 10V T1: TDK PART# LDT565630T-002, LPRI = 14.5µH, N = 10.2 D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED 1 COUT = 20µF 0 2 3468 TA04 3 4 5 6 VIN (V) 7 8 9 3468 TA06 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/LTC3441 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 346812fa 12 Linear Technology Corporation LT/TP 0105 1K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003