LT3485EDD-3 [Linear]
Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive; 闪光灯电容充电器，输出电压监视器和集成IGBT驱动器
| 型号： | LT3485EDD-3 |
| 厂家： | 
Linear |
| 描述： | Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive |
| 文件： | 总20页 (文件大小：332K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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 inte-
grated ICs containing complete charger and IGBT drive
■
Integrated IGBT Driver
■
Voltage Output Monitor
■
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
transformercontrolsthefinalchargevoltage.Whilecharging,
the output voltage on the capacitor may be monitored by a
microcontrollerfromthemonitorpin.Eachdevicecontainsan
on-chiphighvoltageNPNpowerswitch, whichcanwithstand
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
primarycurrentlimitof1.4A,whereastheLT3485-3,LT3485-2,
and LT3485-1 have current limits of 2A, 1A and 0.7A respec-
tively. These different current limits result in tightly controlled
input currents.
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
LT3485-3
LT3485-0
LT3485-2
LT3485-1
INPUT CURRENT (mA)
CHARGE TIME (sec)
750
500
350
225
2.5
3.7
5.5
4.0*
V
= V
= 3.6V
BAT
IN
100µF capacitor, 320V. *50µF capacitor
U
The CHARGE pin gives full control of the part to the user.
DrivingCHARGElowputsthepartinshutdown.TheDONEpin
indicates when the part has completed charging. The LT3485
series of parts are housed in a leadless (3mm × 3mm) DFN
package.
APPLICATIO S
■
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
V
BAT
320V
1:10.2
•
LT3485-0 Charging Waveform
2 AA OR
1
2
4
5
1 TO 2 Li-Ion
4.7µF
1M
•
150µF
PHOTOFLASH
CAPACITOR
A
2.2µF
600V
V
SW
BAT
DONE
V
OUT
50V/DIV
TRIGGER
1
T
FLASHLAMP
CHARGE
GND
3
2
LT3485-0
V
TO
MICRO
CC
C
V
IN
V
MONT
5V
AVERAGE
INPUT CURRENT
0.5A/DIV
IGBTPWR
0.22µF
3485 TA02
V
C
= 3.6V
1s/DIV
IGBT
IGBTIN
IN
OUT
IGBTOUT
= 100µF
3485 TA01
34850123fb
1
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
W W U W
U
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
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
CHARGE
1
2
3
4
5
10
9
V
MONT
V
BAT
DONE
11
V
IN
8
IGBTPWR
IGBTIN
SW
SW
7
6
IGBTOUT
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
V
MONT Voltage ......................................................... 10V
ORDER PART NUMBER
DD PART MARKING
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
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 T = 25°C. V = V
= V
= 3V, unless otherwise noted.
A
IN
BAT
CHARGE
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Quiescent Current
Not Switching
CHARGE
5
0
8
1
mA
µA
V
= 0V
V
V
Voltage Range
●
●
2.5
1.7
10
10
V
V
IN
Voltage Range
BAT
Switch Current Limit
LT3485-3
LT3485-0
LT3485-2
LT3485-1
1.6
1.1
0.75
0.45
1.7
1.2
0.85
0.55
1.8
1.3
0.95
0.65
A
A
A
A
Switch V
LT3485-3, I = 1.5A
310
210
170
100
400
300
225
175
mV
mV
mV
mV
CESAT
SW
LT3485-0, I = 1A
SW
LT3485-2, I = 700mA
SW
LT3485-1, I = 400mA
SW
V
V
Comparator Trip Voltage
Comparator Overdrive
Measured as V – V
●
●
31
10
31.5
200
45
32
V
mV
mV
OUT
OUT
SW
IN
300ns Pulse Width
400
120
DCM Comparator Trip Voltage
CHARGE Pin Current
Measured as V – V
SW
IN
V
V
= 3V
= 0V
65
0
100
0.1
µA
µA
CHARGE
CHARGE
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 T = 25°C. V = V
= V
= 3V, unless otherwise noted.
CHARGE
A
IN
CONDITIONS
= V = 5V, in Shutdown
BAT
PARAMETER
MIN
TYP
MAX
UNITS
Switch Leakage Current
CHARGE Input Voltage High
CHARGE Input Voltage Low
Minimum Charge Pin Low Time
DONE Output Signal High
V
●
●
●
0.01
1
µA
V
IN
SW
1
0.3
V
High→Low→High
20
3
µs
V
100kΩ from V to DONE
IN
DONE Output Signal Low
33µA into DONE Pin
140
20
200
100
mV
DONE Leakage Current
IGBT Input Voltage High
IGBT Input Voltage Low
IGBT Output Rise Time
IGBT Output Fall Time
V
= 3V, DONE NPN Off
nA
V
DONE
●
●
1.5
0.3
V
C
C
= 4000pF, IGBTPWR = 5V, 10%→90%
= 4000pF, IGBTPWR = 5V, 90%→10%
450
340
ns
ns
OUT
OUT
V
Monitor Accuracy
SW – V
SW – V
= 20V
= 30V
610
920
625
940
640
960
mV
mV
OUT
BAT
BAT
Monitor Output Current
200
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.
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.
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
LT3485-2 Charging Waveform
LT3485-0 Charging Waveform
V
V
OUT
50V/DIV
V
OUT
OUT
50V/DIV
50V/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV
AVERAGE
INPUT
CURRENT
1A/DIV
3485 G01
3485 G03
3485 G02
V
C
= 3.6V
0.5s/DIV
V
C
= 3.6V
0.5s/DIV
V
C
= 3.6V
0.5s/DIV
IN
OUT
IN
OUT
IN
OUT
= 50µF
= 50µF
= 50µF
LT3485-0 Input Current
LT3485-3 Charging Waveform
Charge Time
6
600
500
400
300
C
= 50µF
OUT
LT3485-1
5
4
3
2
1
0
LT3485-2
V
OUT
50V/DIV
AVERAGE
INPUT
CURRENT
1A/DIV
200
100
0
3485 G04
2.5V
3.6V
4.2V
V
C
= 3.6V
0.5s/DIV
IN
OUT
= 50µF
LT3485-0
4
LT3485-3
6
2
5
7
8
3
0
150 200 250 300
(V)
50
100
V
(V)
V
OUT
IN
1635 G05
3485 G06
LT3485-1 Input Current
LT3485-2 Input Current
LT3485-3 Input Current
250
200
150
100
50
400
300
200
100
900
800
700
600
500
400
300
200
100
2.5V
3.6V
4.2V
2.5V
3.6V
4.2V
2.5V
3.6V
4.2V
0
0
0
0
50
100 150 200 250 300
(V)
0
50
100 150 200 250 300
(V)
0
50
100 150
200 250 300
V
V
OUT
V
(V)
OUT
OUT
3485 G08
3485 G07
3485 G09
34850123fb
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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.
LT3485-0 Efficiency
LT3485-1 Efficiency
LT3485-2 Efficiency
90
80
70
60
90
80
70
60
90
80
70
60
50
40
50
40
50
40
2.5V
3.6V
4.2V
2.5V
3.6V
4.2V
2.5V
3.6V
4.2V
50
150
V
200
(V)
250
300
100
50
150
V
200
(V)
250
300
50
150
V
OUT
200
(V)
250
300
100
100
OUT
OUT
3485 G12
3485 G10
3485 G11
LT3485-0 Output Voltage
LT3485-3 Efficiency
LT3485-1 Output Voltage
90
80
70
60
322
321
320
319
322
321
320
319
50
40
318
317
318
317
–40°C
25°C
85°C
2.5V
3.6V
4.2V
–40°C
25°C
85°C
50
150
V
200
(V)
250
300
2
4
5
6
7
8
100
3
2
4
5
6
7
8
3
V
(V)
V
(V)
OUT
IN
IN
3485 G13
3485 G14
3485 G15
LT3485-2 Output Voltage
LT3485 Switch Current Limits
LT3485-3 Output Voltage
322
321
320
319
2000
1600
1200
800
400
0
328
327
326
325
324
323
322
LT3485-3
LT3485-0
–40°C
25°C
85°C
LT3485-2
LT3485-1
318
317
–40°C
25°C
85°C
2
4
5
6
7
8
3
2
4
5
6
7
8
–40 –20
0
20
40
60
100
3
80
V
(V)
V
(V)
TEMPERATURE (°C)
IN
IN
3485 G17
3485 G16
3485 G18
34850123fb
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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
LT3485-2 Switching Waveform
V
SW
V
SW
V
SW
10V/DIV
10V/DIV
10V/DIV
I
PRI
I
PRI
I
PRI
1A/DIV
1A/DIV
1A/DIV
3485 G19
3485 G20
3485 G21
V
V
= 3.6V
1µs/DIV
V
V
= 3.6V
1µs/DIV
V
V
= 3.6V
1µs/DIV
IN
OUT
IN
OUT
IN
OUT
= 100V
= 100V
= 100V
LT3485-3 Switching Waveform
LT3485-1 Switching Waveform
LT3485-0 Switching Waveform
V
SW
V
SW
10V/DIV
V
SW
10V/DIV
10V/DIV
I
PRI
I
I
2A/DIV
PRI
PRI
1A/DIV
1A/DIV
3485 G22
V
V
= 3.6V
1µs/DIV
IN
OUT
3485 G23
3485 G24
V
V
= 3.6V
1µs/DIV
V
V
= 3.6V
1µs/DIV
= 100V
IN
OUT
IN
OUT
= 300V
= 300V
LT3485-0/LT3485-1/LT3485-2/
LT3485-3 Switch Breakdown
Voltage
LT3485-2 Switching Waveform
LT3485-3 Switching Waveform
10
9
8
7
6
5
4
3
2
1
0
SW PIN IS RESISTIVE UNTIL BREAKDOWN
VOLTAGE DUE TO INTEGRATED
RESISTORS. THIS DOES NOT INCREASE
QUIESCENT CURRENT OF PART
V
SW
V
SW
10V/DIV
10V/DIV
T = 25°C
I
PRI
I
2A/DIV
PRI
1A/DIV
3485 G26
T = –40°C
T = 85°C
V
V
= 3.6V
1µs/DIV
IN
OUT
3485 G25
V
V
= 3.6V
1µs/DIV
= 300V
IN
OUT
= 300V
V
IN
= V = 5V
CHARGE
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
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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. Oncethetargetvoltageisreached, thepartwillstop
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.
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.
V
BAT (Pin2): BatterySupplyPin. Mustbelocallybypassed
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.
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.
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.
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.
Choose Turns Ratio N by the following equation:
VOUT + 2
N =
31.5
where VOUT is the desired output voltage.
34850123fb
7
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
U
U
W
FU CTIO AL BLOCK DIAGRA
D1
T1
TO BATTERY
C1
V
OUT
PRIMARY
SECONDARY
TO V
IN
C2
SW
4, 5
DONE
V
MONT
9
10
3
2
R2
60k
Q3
CHIP
POWER
SAMPLE
AND HOLD
C
R4
120k
OUT
DCM
COMPARATOR
PHOTOFLASH
CAPACITOR
Q2
+
–
ONE-
SHOT
R3
4k
R1
A3
ENABLE
Q
S
Q
R
2.5k
+
45mV
–
CHARGE
ONE-
1
8
7
+
–
SHOT
A2
IGBT
DRIVER
POWER
1.25V
REFERENCE
TO V
IN
V
OUT
COMPARATOR
DRIVER
S
IGBTIN
R
Q
Q1
IGBT
DRIVER
20Ω
+
+
ONE-
SHOT
R
SENSE
A1
GND
20k
11
–
–
20mV
6
3485 F01
LT3485-3: R
LT3485-0: R
LT3485-2: R
LT3485-1: R
= 0.010Ω
= 0.015Ω
= 0.022Ω
= 0.030Ω
SENSE
SENSE
SENSE
SENSE
TO GATE OF IGBT
Figure 1
34850123fb
8
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
U
OPERATIO
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.
TheLT3485-0/LT3485-1/LT3485-2/LT3485-3aredesigned
tochargephotoflashcapacitorsquicklyandefficiently.The
operation of the part can be best understood by referring
toFigure1.WhentheCHARGEpinisfirstdrivenhigh,aone
shot sets both SR latches in the correct state. The power
NPN device, Q1, turns on and current begins ramping up
intheprimaryoftransformerT1. ComparatorA1monitors
the switch current and when the peak current reaches 2A
(LT3485-3), 1.4A (LT3485-0), 1A (LT3485-2) or 0.7A
(LT3485-1),Q1isturnedoff.SinceT1isutilizedasaflyback
transformer, theflybackpulseontheSWpinwillcausethe
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.
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.
During this phase, current is delivered to the photoflash
capacitor via the secondary and diode D1. As the second-
arycurrentdecreasestozero,theSWpinvoltagewillbegin
tocollapse.WhentheSWpinvoltagedropsto45mVabove
VBAT or lower, the output of A3 (DCM Comparator) will go
low.ThisfiresaoneshotwhichturnsQ1backon.Thiscycle
will continue to deliver power to the output.
The LT3485 VMONT pin functions as an output to a
microcontrollertocommunicatetheprogressofthecharge.
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.
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
deliverycanonlyberestartedbytogglingtheCHARGEpin.
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.
The CHARGE pin gives full control of the part to the user.
The charging can be halted at any time by bringing the
V
OUT
100V/DIV
V
DONE
5V/DIV
V
CHARGE
5V/DIV
3485 F02
LT3485-2
1s/DIV
V
IN
C
OUT
= 3.6V
= 50µF
Figure 2. Halting the Charging Cycle with the CHARGE Pin
34850123fb
9
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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APPLICATIO S I FOR ATIO
Choosing the Right Device
where VOUT is the desired output voltage. The number 2
inthenumeratorisusedtoincludetheeffectofthevoltage
drop across the output diode(s).
(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.
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
LPRI
≥
N •IPK
where VOUT is the desired output voltage. N is the trans-
former turns ratio. IPK is 1.4 (LT3485-0), 0.7 (LT3485-1),
1 (LT3485-2) and 2 (LT3485-3).
Transformer Design
The flyback transformer is a key element for any
LT3485-0/LT3485-1/LT3485-2/LT3485-3design.Itmust
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.
LPRI needs to be equal or larger than this value to ensure
thattheLT3485-0/LT3485-1/LT3485-2/LT3485-3hasad-
equate time to respond to the flyback waveform.
All other parameters need to meet or exceed the recom-
mended limits as shown in Table 1. A particularly impor-
tantparameteristheleakageinductance,LLEAK.Whenthe
power switch of the LT3485-0/LT3485-1/LT3485-2/
LT3485-3 turns off, the leakage inductance on the pri-
mary of the transformer causes a voltage spike to occur
on the SW pin. The height of this spike must not exceed
40V,eventhoughtheabsolutemaximumratingoftheSW
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).
The first transformer parameter that needs to be set is the
turnsratioN.TheLT3485-0/LT3485-1/LT3485-2/LT3485-
3 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 accord-
ing to the following equation:
VOUT + 2
N =
31.5
Table 1. Recommended Transformer Parameters
TYPICAL RANGE
TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE
PARAMETER
NAME
LT3485-0
>5
LT3485-1
>10
LT3485-2
>7
LT3485-3
>3.5
UNITS
µH
L
L
Primary Inductance
PRI
Primary Leakage Inductance
Secondary: Primary Turns Ratio
Secondary to Primary Isolation Voltage
Primary Saturation Current
Primary Winding Resistance
Secondary Winding Resistance
100 to 300
8 to 12
>500
200 to 500
8 to 12
>500
200 to 500
8 to 12
>500
100 to 300
8 to 12
>500
nH
LEAK
N
V
ISO
V
A
I
>1.6
>0.8
>1.0
>2
SAT
R
R
<300
<500
<400
<200
mΩ
Ω
PRI
<40
<80
<60
<30
SEC
34850123fb
10
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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APPLICATIO S I FOR ATIO
Capacitor Selection
Note that the absolute maximum rating of the SW pin is
not exceeded. Make sure to check the SW voltage wave-
formwithVOUT nearthetargetoutputvoltage, asthisisthe
worst case condition for SW voltage. Figure 4 shows the
various limits on the SW voltage during switch turn off.
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
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.
The rectifying diode(s) should be low capacitance type
with sufficient reverse voltage and forward current rat-
ings. The peak reverse voltage that the diode(s) will see is
approximately:
Linear Technology has worked with several leading mag-
netic component manufacturers to produce pre-designed
flyback transformers for use with the LT3485-0/LT3485-
1/LT3485-2/LT3485-3. Table 2 shows the details of sev-
eral of these transformers.
VPK−R = VOUT + (N • V )
IN
“B”
MUST BE
I
PRI
LESS THAN 50V
1A/DIV
2
“A”
MUST BE
LESS THAN 40V
V
SW
0V
V
SW
10A/DIV
3485 F03
3485 F04
V
V
= 5V
100ns/DIV
IN
OUT
= 320V
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
SIZE
L
R
R
SEC
(Ω)
PRI
LPRI-LEAKAGE
PRI
FOR USE WITH
(W × L × H) mm (µH)
(nH)
N
(mΩ)
VENDOR
LT3485-0/LT3485-2
LT3485-1
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
Kijima Musen
Hong Kong Office
852-2489-8266 (ph)
kijimahk@netvigator.com (email)
LT3485-0
LT3485-1
LT3485-2
LT3485-3
LDT565630T-001
LDT565630T-002
LDT565630T-003
LDT565630T-041
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
200 Max
500 Max
550 Max
150 Max
10.4 100 Max 10 Max
10.2 240 Max 16.5 Max
10.2 210 Max 14 Max
10.4 90 Max 6.4 Max
TDK
14.5
10.5
4.7
Chicago Sales Office
(847) 803-6100 (ph)
www.components.tdk.com
LT3485-0/LT3485-1
LT3485-1
LT3485-3
T-15-089
T-15-083
T-17-109A
6.4 × 7.7 × 4.0
8.0 × 8.9 × 2.0
6.5 × 7.9 × 4.0
12
20
5.9
400 Max
500 Max
300 Max
10.2 211 Max 27 Max
10.2 675 Max 35 Max
10.2 78 Max 18.61 Max
Tokyo Coil Engineering
Japan Office
0426-56-6262 (ph)
www.tokyo-coil.co.jp
34850123fb
11
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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APPLICATIO S I FOR ATIO
The peak current of the diode is simply:
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 con-
trols 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 capaci-
tance 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,
2
N
1.4
N
1
N
0.7
N
IPK-SEC
IPK-SEC
IPK-SEC
IPK-SEC
=
=
=
=
LT3485-3
(
)
LT3485-0
(
)
LT3485-2
(
)
LT3485-1
(
)
F
or 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/LT3485-
2/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
numberofdiodestoachievethenecessaryreversebreak-
down voltage.
Table 3. Recommended Output Diodes
MAX REVERSE VOLTAGE MAX FORWARD CONTINUOUS CURRENT
CAPACITANCE
(pF)
PART
(V)
(mA)
VENDOR
GSD2004S
2x300
225
5
5
5
Vishay
(Dual Diode)
(402) 563-6866
www.vishay.com
BAV23S
(Dual Diode)
2x250
2x350
225
225
Philips Semiconductor
(800) 234-7381
www.philips.com
MMBD3004S
(Dual Diode)
Diodes Inc
(816) 251-8800
www.diodes.com
V
BAT
320V
1:10.2
•
2 AA OR
1
2
4
5
1 TO 2 Li-Ion
4.7µF
1M
•
150µF
A
2.2µF
600V
PHOTOFLASH
CAPACITOR
V
SW
BAT
DONE
TRIGGER
1
T
FLASHLAMP
CHARGE
GND
3
2
LT3485-0
V
TO
MICRO
CC
C
V
IN
V
MONT
5V
IGBTPWR
0.22µF
IGBT
IGBTIN
IGBTOUT
3485 F05
Figure 5. Complete Xenon Circuit
34850123fb
12
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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APPLICATIO S I FOR ATIO
GATE
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
whendrivinganIGBTand2mAofquiescentcurrent. Inthe
low state, the IGBT’s quiescent current is less than 0.1µA.
3485 F06
EMITTER
Table 4 is a list of recommended IGBT devices for strobe
applications. These three devices are all packaged in
8-lead TSSOP packages.
Figure 6. IGBT Gate
the capacitance closest to the terminal goes low but the
capacitance further from the terminal remains high. This
causesasmallportionofthedevicetohandlethefull100A
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.
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
voltageproportionaltotheoutputoftheflybackconverter.
The output monitor voltage range for the pin is 0V to 1V.
The 1V output corresponds with the charge cycle termi-
nating and the DONE pin going low. The voltage output
monitor is only functional when the circuit is charging
(DONE and CHARGE are high.)
TheLT3485’sintegrateddrivecircuitisindependentofthe
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)
BREAKDOWN
VOLTAGE
(V)
COLLECTOR
CURRENT
(PULSED) (A)
PART
VENDOR
CY25BAH-8F
CY25BAJ-8F
2.5
4
400
400
150
150
Renesas
(408) 382-7500
www.renesas.com
GT8G133
4
400
150
Toshiba Semiconductor
(949) 623-2900
www.semicon.toshiba.co.jp/eng/
34850123fb
13
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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APPLICATIO S I FOR ATIO
Board Layout
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
leakageinductanceofT1, whichmayresultinanovervolt-
age condition on the SW pin.
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 com-
ponent placement. Keep the area for the high voltage end
ofthesecondaryassmallaspossible. Alsonotethelarger
than minimum spacing for all high voltage nodes in order
V
R1
MONT
CHARGE
DONE
1
2
3
4
5
10
9
C2
C3
V
IN
IGBTPWR
IGBTIN
C
11
8
OUT
PHOTOFLASH
CAPACITOR
+
7
6
IGBTOUT
•
3485 F07
T1
SECONDARY
PRIMARY
•
C1
D1
V
(DUAL DIODE)
BAT
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
T1
1:10.2
D1
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
R1
100k
V
BAT
SW
DONE
DONE
GND
CHARGE
CHARGE
LT3485-0
V
IN
V
IN
V
MONT
2.5V TO 8V
C2
0.22µF
TO MICRO
TO GATE OF IGBT
IGBTPWR
IGBTIN
IGBTOUT
3485 F08
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L = 10µH, N = 10.2
PRI
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
T1
D1
1:10.2
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
R1
100k
V
BAT
SW
DONE
DONE
GND
CHARGE
CHARGE
LT3485-1
V
IN
V
IN
V
MONT
2.5V TO 8V
C2
0.22µF
TO MICRO
IGBTPWR
IGBTIN
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, L = 24µH, N = 10.2
PRI
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
T1
1:10.2
D1
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
R1
100k
V
BAT
SW
DONE
DONE
GND
CHARGE
CHARGE
LT3485-2
V
IN
V
IN
VMONT
2.5V TO 8V
C2
0.22µF
TO MICRO
TO GATE OF IGBT
IGBTPWR
IGBTIN
IGBTOUT
3485 F10
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L = 10µH, N = 10.2
PRI
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
T1
D1
1:10.2
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
R1
100k
V
BAT
SW
DONE
DONE
GND
CHARGE
CHARGE
LT3485-3
V
IN
V
IN
V
MONT
2.5V TO 8V
C2
0.22µF
TO MICRO
IGBTPWR
IGBTIN
IGBTOUT
TO GATE OF IGBT
3485 F11
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-041, L = 4.7µH, N = 10.4
PRI
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
D1
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
V
BAT
SW
DONE
DONE
GND
CHARGE
CHARGE
LT3485-0
V
IN
V
IN
V
MONT
2.5V TO 8V
C2
0.22µF
TO MICRO
TO GATE OF IGBT
IGBTPWR
IGBTIN
IGBTOUT
3485 F12
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-001, L = 6µH, N = 10.4
PRI
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
C
= 50µF
OUT
5
4
3
2
1
0
LT3485-1
LT3485-2
LT3485-0
3
LT3485-3
5
2
4
6
7
8
V
(V)
IN
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
T1
1:10.2
D1
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
V
SW
BAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-1
V
IN
2.5V TO 8V
V
VMONT
IN
C2
0.22µF
TO MICRO
TO GATE OF IGBT
IGBTPWR
IGBTIN
IGBTOUT
3485 F14
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-002, L = 14.5µH, N = 10.2
PRI
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
T1
D1
1:10.2
V
BAT
320V
1.8V TO 8V
C1
4.7µF
C
OUT
PHOTOFLASH
CAPACITOR
V
SW
BAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-2
V
IN
2.5V TO 8V
V
VMONT
IN
C2
0.22µF
TO MICRO
IGBTPWR
IGBTIN
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, L = 10µH, N = 10.2
PRI
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
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
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
0.38 ± 0.10
10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1005
5
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
19
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3407
Dual 600mA (I ), 1.5MHz, Synchronous Step-Down DC/DC 96% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 40µA,
Q
OUT
IN
OUT(MIN)
Converter
I
<1µA, MS10E
SD
LT3420/LT3420-1
LTC3425
1.4A/1A, Photoflash Capacitor Chargers with
Automatic Top-Off
Charges 220µF to 320V in 3.7 seconds from 5V,
V : 2.2V to 16V, I = 90µA, I < 1µA, MS10
IN
Q
SD
5A I , 8MHz, Multi-Phase Synchronous Step-Up DC/DC
95% Efficiency, V : 0.5V to 4.5V, V
= 5.25V, I = 12µA,
SW
IN
OUT(MIN)
Q
Converter
I
< 1µA, QFN-32
SD
LTC3440
600mA/1A (I ), Synchronous Buck-Boost DC/DC
Converter
95% Efficiency, V : 2.5V to 5.5V, V
I = 25µA, I < 1µA, MS-10 DFN-12
Q SD
= 2.5V to 5.5V,
OUT
IN
OUT(MIN)
LT3468/LT3468-1/
LT3468-2
Photoflash Capacitors in ThinSOT™
Charges 110µF to 320V in 4.6 Seconds from 3.6V,
V : 2.5V to 16V, I = 5mA, I < 1µA, ThinSOT
IN
Q
SD
LT3472
Dual ±34V, 1.2MHz Boost (350mA)/Inverting (400mA)
DC/DC Converter for CCD Bias
Integrated Schottkys, V : 2.2V to 16V, V
I = 2.5mA, I < 1µA, DFN
Q SD
= ±34V,
IN
OUT(MAX)
LT3463/LT3463A
Dual Boost (250mA)/Inverting (250mA/400mA)
DC/DC Converter for CCD Bias
Integrated Schottkys, V : 2.3V to 15V, V
IN
= ±40V,
OUT(MAX)
I = 40µA, I < 1µA, DFN
Q
SD
LT3484-0/LT3484-1/
LT3484-2
Photoflash Capacitor Chargers
Charges 110µF to 320V in 4.6 Seconds from 3.6V,
V : 2.5V to 16V, V : 1.8V to 16V, I = 5mA, I < 1µA,
IN
BAT
Q
SD
2mm × 3mm DFN
ThinSOT is a trademark of Linear Technology Corporation.
34850123fb
LT 0406 REV B • PRINTED IN USA
20 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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