LT3468/LT3468-1/LT3468-2 - Photoflash Capacitor Chargers in ThinSOT
Document overview
- Manufacturer or author: Linear Technology Corporation
- PDF pages: 12
Technical content
■ Digital / Film Camera Flash ■ PDA / Cell Phone Flash ■ Emergency Strobe ■ 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 Photoflash Capacitor Chargers in ThinSOT TM 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. 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. DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY LT3468 Photoflash Charger Uses High Efficiency 4mm Tall Transformer LT3468 CHARGE GND VIN SW DONE DONE CHARGE 4.7µF 100k 1:10.2VIN 2.5V TO 8V 320V1
346812 TA01
100µF LT3468 Charging Waveform
3468 G011s/DIV
VIN = 3.6V COUT = 100µF VOUT 50V/DIV AVERAGE INPUT CURRENT 1A/DIV TYPICAL APPLICATIO U , 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.
Operating Temperature Range (Note 2) ...–40 °C to 85°C ORDER PART NUMBER S5 PART MARKINGTJMAX = 125°C θJA = 150°C ON BOARD OVER GROUND PLANE θJC = 90°C/W LTAEC LTAGQ LTBCH LT3468ES5 LT3468ES5-1 LT3468ES5-2 ABSOLUTE AXI U RATI GSW WW U PACKAGE/ORDER I FOR ATIOUU W (Note 1) ELECTRICAL CHARACTERISTICSThe ● 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 MIN TYP MAX UNITS Quiescent Current Not Switching 5 8 mA VCHARGE = 0V 0 1 µA Input Voltage Range ● 2.5 16 V Switch Current Limit LT3468 (Note 3) 1.1 1.2 1.3 A LT3468-2 0.77 0.87 0.97 A LT3468-1 0.45 0.55 0.65 A Switch VCESAT LT3468, ISW = 1A 330 430 mV LT3468-2, ISW = 650mA 210 280 mV LT3468-1, ISW = 400mA 150 200 mV VOUT Comparator Trip Voltage Measured as V SW – VIN ● 31 31.5 32 V VOUT Comparator Overdrive 300ns Pulse Width 200 400 mV DCM Comparator Trip Voltage Measured as V SW – VIN ● 10 36 80 mV CHARGE Pin Current V CHARGE = 3V 15 40 µA VCHARGE = 0V 0 0.1 µA Switch Leakage Current V IN = VSW = 5V, in Shutdown ● 0.01 1 µA CHARGE Input Voltage High ● 1V CHARGE Input Voltage Low ● 0.3 V Minimum Charge Pin Low Time High →Low→High 20 µs DONE Output Signal High 100k Ω from VIN to DONE 3 V DONE Output Signal Low 33 µA into DONE Pin 100 200 mV DONE Leakage Current V DONE = 3V, DONE NPN Off 20 100 nA Consult LTC Marketing for parts specified with wider operating temperature ranges. 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.
5 VIN
4 CHARGE
LT3468-1 Charging Waveform LT3468 Input Current LT3468-1 Input Current LT3468 Charging Waveform LT3468 Charge Time VIN (V) 23456789 CHARGE TIME (s)
3468 G04
COUT = 50µF COUT = 100µF TA = 25°C VIN (V) 23456789 CHARGE TIME (s)
3468 G05
COUT = 20µF COUT = 50µF TA = 25°C VOUT (V) 0 50 100 150 200 250 300 AVERAGE INPUT CURRENT (mA)
3468 G07
VIN = 2.8V VIN = 4.2V VIN = 3.6V TA = 25°C VOUT (V) 0 50 100 150 200 250 300 AVERAGE INPUT CURRENT (mA)
3468 G08
VIN = 2.8V VIN = 4.2V VIN = 3.6V TA = 25°C VIN = 3.6V COUT = 50µF
3468 G01 3468 G02
TYPICAL PERFOR A CE CHARACTERISTICSUW 1s/DIV VIN = 3.6V COUT = 100µF VOUT 50V/DIV 1s/DIV AVERAGE INPUT CURRENT 1A/DIV VOUT 50V/DIV AVERAGE INPUT CURRENT 0.5A/DIV 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. VIN = 3.6V COUT = 100µF VOUT 50V/DIV AVERAGE INPUT CURRENT 0.5A/DIV 1s/DIV
3468 G03
VIN (V) CHARGE TIME (s) 4 6 7
3468 G06
COUT = 100µF COUT = 50µF TA = 25°C VOUT (V) 0 50 100 150 200 250 300 AVERAGE INPUT CURRENT (mA)
3468 G09
VIN = 2.8V VIN = 4.2V VIN = 3.6V TA = 25°C LT3468-2 Charge Time LT3468-2 Charging Waveform LT3468-2 Input Current
LT3468-1 Switch Current Limit LT3468-1 Output VoltageLT3468 Output Voltage LT3468 Switch Current Limit VIN (V) 2345678 VOUT (V)
3468 G13
TA = –40°C TA = 25°C TA = 85°C VIN (V) 2345678 VOUT (V)
3468 G14
TA = –40°C TA = 25°C TA = 85°C TEMPERATURE (°C) –40 –20 0 20 40 60 100 80 ILIM (A)
3468 G16
1.5 1.1 1.2 1.3 1.4 VIN = 3V VOUT = 0V TEMPERATURE (°C) –40 –20 0 20 40 60 100 80 ILIM (A)
3468 G17
0.700 0.500 0.540 0.580 0.620 0.660 VIN = 3V VOUT = 0V TYPICAL PERFOR A CE CHARACTERISTICSUW 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 LT3468-1 Efficiency VOUT (V) 50 100 150 200 250 300 EFFICIENCY (%)
3468 G10
VIN = 2.8V VIN = 4.2V TA = 25°C VIN = 3.6V VOUT (V) 50 100 150 200 250 300 EFFICIENCY (%)
3468 G11
VIN = 2.8V VIN = 4.2V VIN = 3.6V TA = 25°C TEMPERATURE (°C) –40 ILIM (A) 1.00 0.96 0.92 0.88 0.84 0.80 0 40 60
34682 G18
–20 20 80 100 VIN = 3V VOUT = 0V VOUT (V) EFFICIENCY (%) 250
3468 G12
TA = 25°C VIN = 4.2V VIN = 2.8V VIN = 3.6V VIN (V) VOUT (V) 319 318 317 316 315 314 313 312
3468 G15
TA = 25°C TA = 85°C TA = –40 °C LT3468-2 Switch Current Limit LT3468-2 Output Voltage LT3468-2 Efficiency
LT3468-1 Switching Waveform VIN = 3.6V VOUT = 100V
3468 G191µs/DIV
VIN = 3.6V VOUT = 300V
3468 G231µs/DIV
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. TYPICAL PERFOR A CE CHARACTERISTICS UW VSW 10V/DIV IPRI 1A/DIV 1µs/DIV 3468 G21 VIN = 3.6V VOUT = 100V VSW 10V/DIV IPRI 1A/DIV 1µs/DIV 3468 G24 VIN = 3.6V VOUT = 300V SWITCH VOLTAGE (V) 0 1 02 03 04 05 06 07 08 09 0 1 0 0 SWITCH CURRENT (mA)
3468 G25
T = –40°C T = 25°C T = 85°C SW PIN IS RESISTIVE UNTIL BREAKDOWN VOLTAGE DUE TO INTEGRATED RESISTORS. THIS DOES NOT INCREASE QUIESCENT CURRENT OF PARTVIN = VCHARGE = 5V LT3468 Switching Waveform
3468 G201µs/DIV
VIN = 3.6V VOUT = 300V LT3468-1 Switching Waveform VIN = 3.6V VOUT = 100V
3468 G221µs/DIV
LT3468-2 Switching Waveform LT3468-2 Switching Waveform
SW (Pin 1): Switch Pin. This is the collector of the internal NPN Power switch. Minimize the metal trace area con- nected 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. 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. 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. V IN (Pin 5): Input Supply Pin. Must be locally bypassed with a good quality ceramic capacitor. Input supply must be 2.5V or higher. UUUPI FU CTIO S BLOCK DIAGRA W VIN SW +DONE CHARGE 60k ENABLE COUT PHOTOFLASH CAPACITOR 36mV 20mV TO BATTERY VOUT LT3468: RSENSE = 0.015Ω LT3468-2: RSENSE = 0.022Ω LT3468-1: RSENSE = 0.03Ω 3486 BD GND 4 2 ONE- SHOT ONE- SHOT DRIVER PRIMARY SECONDARY MASTER LATCH RSENSE DCM COMPARATOR VOUT COMPARATOR 2.5k SRQ 1.25V REFERENCE Q1QQ SR CHIP ENABLE Figure 1
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. to respond to the flyback waveform. voltage during switch turn off. effect the charge time of the photoflash circuit. Figure 4. New Transformer Design Check (Not to Scale).Figure 3. LT3468 SW Voltage Waveform
3468 G18100ns/DIV
Table 1. Recommended Transformer Parameters
3420 F07
Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted. achieve the necessary reverse breakdown voltage. The diode D2 in Figure 6 is needed to clamp the SW node. Table 3. Recommended Output Diodes
will not get advertised performance with careless layout. Figure 5 shows the recommended component placement. down voltage requirements for the circuit board. Figure 5. Suggested Layout: Keep Electrical Path Formed by C1,
3468 F05
Table 4. Recommended Clamp Diodes should be 600mV or less at 500mA of forward current. shows various recommended clamping diodes.
3468 F06
3468 F07
Figure 6. LT3468 Photoflash Charger Uses Figure 7. LT3468-1 Photoflash Charger Uses
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3468 F08
Figure 8. LT3468-2 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
5 PLCS (NOTE 3)
2.90 BSC
0.95 BSC
1.90 BSC
1.00 MAX
- DIMENSIONS ARE IN MILLIMETERS
- DIMENSIONS ARE INCLUSIVE OF PLATING
- DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
- MOLD FLASH SHALL NOT EXCEED 0.254mm
- JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
1.22 REF
Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003 LT/TP 0105 1K REV A • PRINTED IN USA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3407 Dual 600mA (I OUT), 1.5MHz, Synchronous Step-Down DC/DC 96% Efficiency, V IN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 40µA, Converter I SD: <1µA, MS10E LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Chargers with Charges 220 µF to 320V in 3.7 seconds from 5V, Automatic Top-Off V IN: 2.2V to 16V, IQ: 90µA, ISD: <1µA, MS10 LTC3425 5A I SW, 8MHz, Multi-Phase Synchronous Step-Up DC/DC 95% Efficiency, V IN: 0.5V to 4.5V, VOUT(MIN): 5.25V, IQ: 12µA, Converter I SD: <1µA, QFN-32 LTC3440/LTC3441 600mA/1A (I OUT), Synchronous Buck-Boost DC/DC Converter 95% Efficiency, V IN: 2.5V to 5.5V, VOUT(MIN): 2.5V to 5.5V, IQ: 25µA, ISD: <1µA, MS-10, DFN-12 TYPICAL APPLICATIO SU LT3468 Photoflash Circuit uses Tiny 3mm Tall Transformer LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer LT3468 CHARGE GND VIN SW DONE DONE CHARGE 4.7µF 100k 1:10.4 COUT PHOTOFLASH CAPACITOR VIN 2.5V TO 8V 320V 5, 6 7, 8 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
3468 TA03
4.7µF 100k 1:10.2 COUT PHOTOFLASH CAPACITOR VIN 2.5V TO 8V 320V 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
3468 TA04
VIN (V) 23456789 CHARGE TIME (s)
3468 TA05
COUT = 50µF COUT = 100µF VIN (V) 23456789 CHARGE TIME (s)
3468 TA06
COUT = 20µF COUT = 50µF