LT3468 Linear Technology, LT3468 Datasheet
LT3468
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LT3468 Summary of contents
Page 1
... 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 while the LT3468-1 has a 0.7A limit. These different current limit levels result in well controlled input currents of 500mA for the LT3468 and 225mA for the LT3468-1 ...
Page 2
... Operating Temperature Range (Note 2) ...– Storage Temperature Range ..................– 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T are for both the LT3468 and LT3468-1 unless otherwise noted. PARAMETER Quiescent Current Input Voltage Range Switch Current Limit ...
Page 3
... W U TYPICAL PERFOR A CE CHARACTERISTICS LT3468-1 curves use the circuit of Figure 2 unless otherwise noted. LT3468 Charging Waveform 100 F OUT V OUT 50V/DIV AVERAGE INPUT CURRENT 1A/DIV 1s/DIV 3468 G01 LT3468-1 Charge Time OUT ...
Page 4
... LT3468/LT3468 TYPICAL PERFOR A CE CHARACTERISTICS LT3468-1 curves use the circuit of Figure 2 unless otherwise noted. LT3468 Output Voltage 324 T = –40 C 323 A 322 321 320 319 318 (V) IN 3468 G09 LT3468-1 Switch Current Limit 0.700 ...
Page 5
... 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. LT3468/LT3468-1 GND (Pin 2): Ground. Tie directly to local ground plane. DONE (Pin 3): Open NPN Collector Indication Pin. When target output voltage is reached, NPN turns on ...
Page 6
... T1. Comparator A1 monitors the switch cur- rent and when the peak current reaches 1.4A (LT3468) or 0.7A (LT3468-1 turned off. Since T1 is utilized as a flyback transformer, the flyback pulse on the SW pin will cause the output high. The voltage on the SW pin needs least 36mV higher than V happen ...
Page 7
... LT3468-1 can use a physically smaller transformer. Transformer Design The flyback transformer is a key element for any LT3468/ LT3468-1 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 ...
Page 8
... NPN is zero. Figure 4 shows the SW voltage waveform for the circuit of Figure 1(LT3468). Note that the absolute maxi- mum rating of the SW pin is not exceeded. Figure 5 shows the SW voltage waveform for the circuit of Figure 2(LT3468- 1). Again, the absolute maximum rating of the SW pin ...
Page 9
... SW Pin Clamp Diode Selection The diode D2 in Figure 1 is needed to clamp the SW node. Due to the new control scheme of the LT3468/LT3468-1, 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 opera- tion of the circuit ...
Page 10
... IN R1 DONE CHARGE 4 5 Figure 6. Suggested Layout: Keep electrical path formed by C1, Transformer Primary and LT3468/LT3468-1 short all high voltage nodes in order to meet breakdown voltage requirements for the circuit board imperative to keep the electrical path formed by C1, the primary of T1, and the LT3468/LT3468-1 as short as possible ...
Page 11
... MIN (NOTE 4) PIN ONE 0.95 BSC 0.90 – 1.30 0.90 – 1.45 0.09 – 0.20 (NOTE 3) ATTENTION: ORIGINAL SOT23-5L PACKAGE. MOST SOT23-5L PRODUCTS CONVERTED TO THIN SOT23 PACKAGE, DRAWING # 05-08-1635 AFTER APPROXIMATELY APRIL 2001 SHIP DATE LT3468/LT3468-1 2.80 – 3.10 (NOTE 4) 0.25 – 0.50 TYP 5 PLCS NOTE 3 0.00 – 0.15 1.90 BSC S5 SOT-23 0502 34681i 11 ...
Page 12
... GND 4 CHARGE CHARGE C1: 4.7 F, X5R OR X7R, 10V T1: TDK PART# LDT565630T-001 10.4 PRI D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer T1 1: ...