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LT3485-0/LT3485-1/ LT3485-2/LT3485-3 Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive
FEATURES

DESCRIPTIO
Integrated IGBT Driver Voltage Output Monitor Uses Small Transformers: 5.8mm x 5.8mm x 3mm Operates from Two AA Batteries, Single Cell Li-Ion or Any Supply from 1.8V up to 16V No Output Voltage Divider Needed No External Schottky Diode Required Charges Any Size Photoflash Capacitor Available in 10-Lead (3mm x 3mm) DFN
VERSION LT3485-3 LT3485-0 LT3485-2 LT3485-1 INPUT CURRENT (mA) 750 500 350 225 CHARGE TIME (sec) 2.5 3.7 5.5 4.0*
Fast Charge Time
VIN = VBAT = 3.6V 100F capacitor, 320V. *50F capacitor
The LT(R)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. 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 x 3mm) DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6636021.
APPLICATIO S
Digital Camera and Cell Phone Flash Charger
TYPICAL APPLICATIO
VBAT 2 AA OR 1 TO 2 Li-Ion 1:10.2 1 4.7F 2 VBAT DONE CHARGE GND LT3485-0 VCC 5V 0.22F VIN IGBTPWR IGBTIN IGBTOUT VMONT SW
LT3485-0 Photoflash Charger Uses High Efficiency 3mm Tall Transformers
DANGER HIGH VOLTAGE - OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
320V 4 1M 150F PHOTOFLASH CAPACITOR 2.2F 600V TRIGGER T 1 2 TO MICRO 3 C
AVERAGE INPUT CURRENT 0.5A/DIV
* *
5
A
VOUT 50V/DIV
FLASHLAMP
IGBT
3485 TA01
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LT3485-0 Charging Waveform
VIN = 3.6V COUT = 100F 1s/DIV
3485 TA02
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34850123f
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW CHARGE VBAT VIN SW SW 1 2 3 4 5 11 10 VMONT 9 DONE 8 IGBTPWR 7 IGBTIN 6 IGBTOUT
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 .......................... 125C Operating Temperature Range (Note 2) ... -40C to 85C Storage Temperature Range .................. -65C to 125C
DD PACKAGE 10-LEAD (3mm 3mm) PLASTIC DFN
TJMAX = 125C JA = 43C/W EXPOSED PAD (11) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER LT3485EDD-0 LT3485EDD-1 LT3485EDD-2 LT3485EDD-3
DD PART MARKING 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
PARAMETER Quiescent Current VIN Voltage Range VBAT Voltage Range Switch Current Limit
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
CONDITIONS Not Switching VCHARGE = 0V

MIN
TYP 5 0
2.5 1.7 1.6 1.1 0.75 0.45 1.7 1.2 0.85 0.55 310 210 170 100 31.5 200 45 65 0
MAX 8 1 10 10 1.8 1.3 0.95 0.65 400 300 225 175 32 400 120 100 0.1
UNITS mA A V V A A A A mV mV mV mV V mV mV A A
Switch VCESAT
VOUT Comparator Trip Voltage VOUT Comparator Overdrive DCM Comparator Trip Voltage CHARGE Pin Current
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 300ns Pulse Width Measured as VSW - VIN VCHARGE = 3V VCHARGE = 0V

31 10
34850123f
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
PARAMETER Switch Leakage Current CHARGE Input Voltage High CHARGE Input Voltage Low Minimum Charge Pin Low Time DONE Output Signal High DONE Output Signal Low DONE Leakage Current IGBT Input Voltage High IGBT Input Voltage Low IGBT Output Rise Time IGBT Output Fall Time VOUT Monitor Accuracy Monitor Output Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. COUT = 4000pF, IGBTPWR = 5V, 10%90% COUT = 4000pF, IGBTPWR = 5V, 90%10% SW - VBAT = 20V SW - VBAT = 30V HighLowHigh 100k from VIN to DONE 33A into DONE Pin VDONE = 3V, DONE NPN Off

ELECTRICAL CHARACTERISTICS
CONDITIONS VIN = VSW = 5V, in Shutdown
MIN

TYP 0.01
MAX 1 0.3
UNITS A V V s V
1 20 3 140 20 1.5 0.3 200 130 610 920 270 180 625 940 200 320 230 640 960 200 100
mV nA V V ns ns mV mV A
Note 2: The LTC3485E-X is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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. LT3485-0 Charging Waveform LT3485-1 Charging Waveform LT3485-2 Charging Waveform
TYPICAL PERFOR A CE CHARACTERISTICS
VOUT 50V/DIV
AVERAGE INPUT CURRENT 1A/DIV VIN = 3.6V COUT = 50F
0.5s/DIV
LT3485-3 Charging Waveform
CHARGE TIME (SECONDS)
VOUT 50V/DIV
4 3 2 1
INPUT CURRENT (mA)
AVERAGE INPUT CURRENT 1A/DIV V = 3.6V IN COUT = 50F
0.5s/DIV
LT3485-1 Input Current
250
400
200
INPUT CURRENT (mA)
INPUT CURRENT (mA)
INPUT CURRENT (mA)
150
100
50
0 0 50 100 150 200 VOUT (V) 250 300
3485 G07
4
UW
2.5V 3.6V 4.2V
VOUT 50V/DIV
VOUT 50V/DIV
3485 G01
AVERAGE INPUT CURRENT 0.5A/DIV VIN = 3.6V COUT = 50F
0.5s/DIV
3485 G02
AVERAGE INPUT CURRENT 0.5A/DIV V = 3.6V IN COUT = 50F
0.5s/DIV
3485 G03
Charge Time
6
LT3485-0 Input Current
COUT = 50F
600 500
LT3485-1
5
LT3485-2
400 300 200 100 2.5V 3.6V 4.2V 0 50 100 150 200 VOUT (V) 250 300
3485 G06
3485 G04
LT3485-0
0 2 3 4
LT3485-3
5 VIN (V) 6
7
8
1635 G05
0
LT3485-2 Input Current
900 800
300
LT3485-3 Input Current
700 600 500 400 300 200 100 0 0 50 100 150 200 VOUT (V) 250 300
3485 G09
200
100 2.5V 3.6V 4.2V 0 0 50 100 150 200 VOUT (V) 250 300
3485 G08
2.5V 3.6V 4.2V
34850123f
LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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. LT3485-0 Efficiency
90 90
TYPICAL PERFOR A CE CHARACTERISTICS
LT3485-1 Efficiency
80
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
50
100
150 200 VOUT (V)
250
LT3485-3 Efficiency
90 322
80 EFFICIENCY (%)
VOUT (V)
60
319
VOUT (V)
70
50
40
50
100
150 200 VOUT (V)
250
LT3485-2 Output Voltage
328 327 326 VOUT (V) 325 324 323 322 318 -40C 25C 85C 322
CURRENT LIMIT (mA)
VOUT (V)
2
3
4
5 VIN (V)
6
UW
2.5V 3.6V 4.2V 300
3485 G10
LT3485-2 Efficiency
90
80
80
70
70
60
60
50
2.5V 3.6V 4.2V 50 100 150 200 VOUT (V) 250 300
3485 G11
50
2.5V 3.6V 4.2V 50 100 150 200 VOUT (V) 250 300
3485 G12
40
40
LT3485-0 Output Voltage
322
LT3485-1 Output Voltage
321
321
320
320
319
2.5V 3.6V 4.2V 300
3485 G13
318
-40C 25C 85C 2 3 4 5 VIN (V) 6 7 8
3485 G14
318
-40C 25C 85C 2 3 4 5 VIN (V) 6 7 8
3485 G15
317
317
LT3485-3 Output Voltage
2000
LT3485 Switch Current Limits
LT3485-3
321
1600 LT3485-0 LT3485-2 800 LT3485-1 400
320
1200
319
-40C 25C 85C 2 3 4 5 VIN (V) 6 7 8
3485 G17
317 7 8
3485 G16
0 -40
-20
40 20 0 60 TEMPERATURE (C)
80
100
3485 G18
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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. LT3485-0 Switching Waveform LT3485-1 Switching Waveform LT3485-2 Switching Waveform
TYPICAL PERFOR A CE CHARACTERISTICS
VSW 10V/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 100V 1s/DIV
3485 G19
LT3485-3 Switching Waveform
VSW 10V/DIV IPRI 2A/DIV VIN = 3.6V VOUT = 100V 1s/DIV
3485 G22
LT3485-2 Switching Waveform
SWITCH CURRENT (mA)
VSW 10V/DIV
IPRI 1A/DIV VIN = 3.6V VOUT = 300V 1s/DIV
3485 G25
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VSW 10V/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 100V 1s/DIV
3485 G20
VSW 10V/DIV IPRI 1A/DIV VIN = 3.6V VOUT = 100V 1s/DIV
3485 G21
LT3485-0 Switching Waveform
LT3485-1 Switching Waveform
VSW 10V/DIV
VSW 10V/DIV
IPRI 1A/DIV VIN = 3.6V VOUT = 300V 1s/DIV
3485 G23
IPRI 1A/DIV VIN = 3.6V VOUT = 300V 1s/DIV
3485 G24
LT3485-3 Switching Waveform
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LT3485-0/LT3485-1/LT3485-2/ LT3485-3 Switch Breakdown Voltage
SW PIN IS RESISTIVE UNTIL BREAKDOWN 9 VOLTAGE DUE TO INTEGRATED RESISTORS. THIS DOES NOT INCREASE 8 QUIESCENT CURRENT OF PART 7 6 5 4 3 2 1 0 0 VIN = VCHARGE = 5V 10 20 30 40 50 60 70 80 90 100 SWITCH VOLTAGE (V)
3485 G27
VSW 10V/DIV IPRI 2A/DIV VIN = 3.6V VOUT = 300V 1s/DIV
3485 G26
T = 25C
T = -40C
T = 85C
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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= VOUT + 2 31.5
where VOUT is the desired output voltage.
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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.
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
FU CTIO AL BLOCK DIAGRA
TO BATTERY TO VIN C2 DONE 9 Q3 SAMPLE AND HOLD 10 VMONT 3 C1
CHIP POWER Q2 R3 4k R4 120k ONESHOT DCM COMPARATOR A3
Q S CHARGE ONESHOT
Q R
ENABLE
1
A2 TO VIN 8 IGBT DRIVER POWER VOUT COMPARATOR
IGBTON
7 IGBT DRIVER 20
20k
6
3485 F01
TO GATE OF IGBT
LT3485-3: RSENSE = 0.010 LT3485-0: RSENSE = 0.015 LT3485-2: RSENSE = 0.022 LT3485-1: RSENSE = 0.030
8
W
T1 PRIMARY D1 VOUT SECONDARY SW 4, 5 2 R2 60k COUT PHOTOFLASH CAPACITOR
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+ - + -
60mV
R1 2.5k
+ -
1.25V REFERENCE DRIVER R S Q Q1
+
ONESHOT A1 RSENSE GND 11
- +-
20mV
Figure 1
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
OPERATIO U
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 = 50F 1s/DIV
3485 F02
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 60mV 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 60mV 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
Figure 2. Halting the Charging Cycle with the CHARGE Pin
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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
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 H nH V A m
10
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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
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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).
34850123f
LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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. 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. 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.
IPRI 1A/DIV
2
VSW
VSW 10A/DIV
VIN = 5V VOUT = 320V
100ns/DIV
3485 F03
Figure 3. LT3485 SW Voltage Waveform
Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted
FOR USE WITH LT3485-0/LT3485-2 LT3485-1 TRANSFORMER NAME SBL-5.6-1 SBL-5.6S-1 SIZE (W x L x H) mm 5.6 x 8.5 x 4.0 5.6 x 8.5 x 3.0 5.8 x 5.8 x 3.0 5.8 x 5.8 x 3.0 5.8 x 5.8 x 3.0 5.8 x 5.8 x 3.0 6.4 x 7.7 x 4.0 8.0 x 8.9 x 2.0 6.5 x 7.9 x 4.0 LPRI (H) 10 24
LPRI-LEAKAGE
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
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Capacitor Selection For the input bypass capacitors, high quality X5R or X7R types 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 )
"B" "A" MUST BE LESS THAN 50V MUST BE LESS THAN 40V 0V
3485 F04
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Figure 4. New Transformer Design Check (Not to Scale)
(nH) 200 Max 400 Max
N 10.2 10.2
RPRI (m) 103 305
RSEC () 26 55
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) kijimahk@netvigator.com (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
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
APPLICATIO S I FOR ATIO
The peak current of the diode is simply:
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 VIN = BAV23S dual silicon5V diodes. Table 3 shows the various VOUT = 320V diodes and relevant specifications. Use the appropriate number of diodes to achieve the necessary reverse breakdown voltage.
Table 3. Recommended Output Diodes
PART GSD2004S (Dual Diode) BAV23S (Dual Diode) MMBD3004S (Dual Diode) MAX REVERSE VOLTAGE (V) 2x300
MAX FORWARD CONTINUOUS CURRENT (mA) 225
2x250
2x350
VBAT 2 AA OR 1 TO 2 Li-Ion
4.7F 2 VBAT DONE CHARGE GND LT3485-0 SW
VCC 5V 0.22F
VIN IGBTPWR IGBTIN
VMONT
IGBTOUT
3485 F05
Figure 5. Complete Xenon Circuit
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IGBT Drive 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 2s 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,
CAPACITANCE (pF) 5 225 5 225 5 VENDOR Vishay (402) 563-6866 www.vishay.com Philips Semiconductor (800) 234-7381 www.philips.com Diodes Inc (816) 251-8800 www.diodes.com
1:10.2 1 320V 4 1M 150F PHOTOFLASH CAPACITOR 2.2F 600V TRIGGER T 1 2 TO MICRO 3 C A
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FLASHLAMP
IGBT
LT3485-0/LT3485-1/ LT3485-2/LT3485-3
APPLICATIO S I FOR ATIO
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. Recommended IGBTs
DRIVE VOLTAGE (V) 2.5 4 4 BREAKDOWN VOLTAGE (V) 400 400 400
PART CY25BAH-8F CY25BAJ-8F GT8G133
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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 0.1A. 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.)
COLLECTOR CURRENT (PULSED) (A) 150 150 150 VENDOR Renesas (408) 382-7500 www.renesas.com Toshiba Semiconductor (949) 623-2900 www.semicon.toshiba.co.jp/eng/
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
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
D1 (DUAL DIODE)
Figure 7. Suggested Layout: Keep Electrical Path Formed by C1, Transformer Primary and LT3485-0/LT3485-1/LT3485-2/LT3485-3 Short
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+
COUT PHOTOFLASH CAPACITOR
VIN
SECONDARY
T1
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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.
CHARGE VMONT R1 DONE 1 C2 2 3 4 5 11 10 9 8 7 6
3485 F07
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C3 IGBTPWR IGBTIN IGBTOUT
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PRIMARY C1
VBAT
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
TYPICAL APPLICATIO S
VBAT 1.8V TO 8V T1 1:10.2 C1 4.7F COUT PHOTOFLASH CAPACITOR D1 320V
VIN 2.5V TO 8V
Figure 8. LT3485-0 Photoflash Charger Uses High Efficiency 4mm Tall Transformer
VIN 2.5V TO 8V
Figure 9. LT3485-1 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
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R1 100k DONE CHARGE
VBAT DONE CHARGE LT3485-0 VIN
SW
GND
C2 0.22F
VMONT IGBTOUT
IGBTPWR
IGBTIN
TO MICRO TO GATE OF IGBT
3485 F08
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10H, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
VBAT 1.8V TO 8V
T1 1:10.2 C1 4.7F
D1 320V
R1 100k DONE CHARGE
VBAT DONE CHARGE LT3485-1 VIN
SW
COUT PHOTOFLASH CAPACITOR
GND
C2 0.22F
VMONT IGBTOUT
IGBTPWR
IGBTIN
TO MICRO TO GATE OF IGBT
3485 F09
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6S-1, LPRI = 24H, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
TYPICAL APPLICATIO S
VBAT 1.8V TO 8V T1 1:10.2 C1 4.7F COUT PHOTOFLASH CAPACITOR D1 320V
VIN 2.5V TO 8V
Figure 10. LT3485-2 Photoflash Charger Uses High Efficiency 4mm Tall Transformer
VIN 2.5V TO 8V
Figure 11. LT3485-3 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
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R1 100k DONE CHARGE
VBAT DONE CHARGE LT3485-2 VIN
SW GND
C2 0.22F
VMONT IGBTOUT
IGBTPWR
IGBTIN
TO MICRO TO GATE OF IGBT
3485 F10
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10H, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
VBAT 1.8V TO 8V
T1 1:10.2 C1 4.7F
D1 320V
R1 100k DONE CHARGE
VBAT DONE CHARGE LT3485-3 VIN
SW
COUT PHOTOFLASH CAPACITOR
GND
C2 0.22F
VMONT IGBTOUT
IGBTPWR
IGBTIN
TO MICRO TO GATE OF IGBT
3485 F11
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: TDK LDT565630T-041, LPRI = 4.7H, N = 10.4 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
TYPICAL APPLICATIO S
VBAT 1.8V TO 8V T1 1:10.2 C1 4.7F COUT PHOTOFLASH CAPACITOR D1 320V
VIN 2.5V TO 8V
Figure 12. LT3485-0 Photoflash Circuit Uses Tiny 3mm Tall Transformer
CHARGE TIME (SECONDS)
Figure 13. Charge Time with TDK Transformers (Figures 11, 12, 13, 14 and 15)
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VBAT DONE CHARGE DONE CHARGE LT3485-0 VIN C2 0.22F
SW
GND
VMONT IGBTOUT
IGBTPWR
IGBTIN
TO MICRO TO GATE OF IGBT
3485 F12
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: TDK LDT565630T-001, LPRI = 6H, N = 10.4 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
6 5 LT3485-1 4 LT3485-2 3 2 1 LT3485-0 0 2 3 4 LT3485-3 5 VIN (V) 6
COUT = 50F
7
8
3485 F13
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
TYPICAL APPLICATIO S
VBAT 1.8V TO 8V T1 1:10.2 C1 4.7F COUT PHOTOFLASH CAPACITOR D1 320V
VIN 2.5V TO 8V
Figure 14. LT3485-1 Photoflash Circuit Uses Tiny 3mm Tall Transformer
VIN 2.5V TO 8V
Figure 15. LT3485-2 Photoflash Circuit Uses Tiny 3mm Tall Transformer
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VBAT DONE CHARGE DONE CHARGE LT3485-1 VIN C2 0.22F
SW
GND
VMONT TO MICRO IGBTOUT TO GATE OF IGBT
3485 F14
IGBTPWR
IGBTIN
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: TDK LDT565630T-002, LPRI = 14.5H, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
VBAT 1.8V TO 8V
T1 1:10.2 C1 4.7F
D1 320V
VBAT DONE CHARGE DONE CHARGE LT3485-2 VIN C2 0.22F
SW
COUT PHOTOFLASH CAPACITOR
GND
VMONT TO MICRO IGBTOUT TO GATE OF IGBT
3485 F15
IGBTPWR
IGBTIN
C1: 4.7F, X5R OR X7R, 10V C2: 0.22F, X5R or X7R, 10V T1: TDK LDT565630T-003, LPRI = 10H, N = 10.2 D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
PACKAGE DESCRIPTIO
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 10 0.38 0.10
PIN 1 TOP MARK (SEE NOTE 6) 5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES) 1
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
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.
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DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
0.675 0.05 3.00 0.10 (4 SIDES) 1.65 0.10 (2 SIDES)
(DD10) DFN 1103
0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD
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LT3485-0/LT3485-1/ LT3485-2/LT3485-3
RELATED PARTS
PART NUMBER LTC3407 LT3420/LT3420-1 LTC3425 LTC3440 LT3468/LT3468-1/ LT3468-2 LT3472 LT3463/LT3463A LT3484-0/LT3484-1/ LT3484-2 DESCRIPTION Dual 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 1.4A/1A, Photoflash Capacitor Chargers with Automatic Top-Off 5A ISW, 8MHz, Multi-Phase Synchronous Step-Up DC/DC Converter 600mA/1A (IOUT), Synchronous Buck-Boost DC/DC Converter Photoflash Capacitors in ThinSOTTM Dual 34V, 1.2MHz Boost (350mA)/Inverting (400mA) DC/DC Converter for CCD Bias Dual Boost (250mA)/Inverting (250mA/400mA) DC/DC Converter for CCD Bias Photoflash Capacitor Chargers COMMENTS 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, MS10E Charges 220F to 320V in 3.7 seconds from 5V, VIN: 2.2V to 16V, IQ = 90A, ISD < 1A, MS10 95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MIN) = 5.25V, IQ = 12A, ISD < 1A, QFN-32 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V to 5.5V, IQ = 25A, ISD < 1A, MS-10 DFN-12 Charges 110F to 320V in 4.6 Seconds from 3.6V, VIN: 2.5V to 16V, IQ = 5mA, ISD < 1A, ThinSOT Integrated Schottkys, VIN: 2.2V to 16V, VOUT(MAX) = 34V, IQ = 2.5mA, ISD < 1A, DFN Integrated Schottkys, VIN: 2.3V to 15V, VOUT(MAX) = 40V, IQ = 40A, ISD < 1A, DFN Charges 110F to 320V in 4.6 Seconds from 3.6V, VIN: 2.5V to 16V, VBAT: 1.8V to 16V, IQ = 5mA, ISD < 1A, 2mm x 3mm DFN
ThinSOT is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
LT/LWI/TP 0805 500 * PRINTED IN USA
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005

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