LT3485-0/LT3485-1/
LT3485-2/LT3485-3
1
34850123fb
FEATURES
DESCRIPTIO
U
Photoflash Capacitor
Chargers with Output Voltage
Monitor and Integrated IGBT Drive
TYPICAL APPLICATIO
U
■
Integrated IGBT Driver
■
Voltage Output Monitor
■
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
APPLICATIO S
U
■
Digital Camera and Cell Phone Flash Charger
The LT
®
3485 family of photoflash chargers are highly inte-
grated 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 V
BAT
pin, which allows
the use of two AA cells to charge the capacitor. The internal
circuitry operates from the V
IN
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 respec-
tively. 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 × 3mm) DFN
package.
Fast Charge Time
VERSION INPUT CURRENT (mA) CHARGE TIME (sec)
LT3485-3 750 2.5
LT3485-0 500 3.7
LT3485-2 350 5.5
LT3485-1 225 4.0*
V
IN
= V
BAT
= 3.6V
100µF capacitor, 320V. *50µF capacitor
LT3485-0
IGBTOUT
IGBTIN
V
IN
IGBTPWR
GND
V
MONT
V
BAT
SW
4.7µF
1:10.2
•
•
V
BAT
2 AA OR
1 TO 2 Li-Ion
0.22µF
V
CC
5V
320V
TO
MICRO
1
T
C
A
23
1
2
4
5
3485 TA01
150µF
PHOTOFLASH
CAPACITOR
2.2µF
600V
1M
CHARGE
DONE TRIGGER FLASHLAMP
IGBT
, 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.
LT3485-0 Charging Waveform
LT3485-0 Photoflash Charger Uses High Efficiency 3mm Tall Transformers
DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
V
IN
= 3.6V
C
OUT
= 100µF
V
OUT
50V/DIV
AVERAGE
INPUT CURRENT
0.5A/DIV 1s/DIV
3485 TA02
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
2
34850123fb
V
IN
Voltage .............................................................. 10V
V
BAT
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
V
MONT
Voltage ......................................................... 10V
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
ABSOLUTE AXI U RATI GS
W
WW
U
(Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Quiescent Current Not Switching 5 8 mA
V
CHARGE
= 0V 0 1 µA
V
IN
Voltage Range ●2.5 10 V
V
BAT
Voltage Range ●1.7 10 V
Switch Current Limit LT3485-3 1.6 1.7 1.8 A
LT3485-0 1.1 1.2 1.3 A
LT3485-2 0.75 0.85 0.95 A
LT3485-1 0.45 0.55 0.65 A
Switch V
CESAT
LT3485-3, I
SW
= 1.5A 310 400 mV
LT3485-0, I
SW
= 1A 210 300 mV
LT3485-2, I
SW
= 700mA 170 225 mV
LT3485-1, I
SW
= 400mA 100 175 mV
V
OUT
Comparator Trip Voltage Measured as V
SW
– V
IN
●31 31.5 32 V
V
OUT
Comparator Overdrive 300ns Pulse Width 200 400 mV
DCM Comparator Trip Voltage Measured as V
SW
– V
IN
●10 45 120 mV
CHARGE Pin Current V
CHARGE
= 3V 65 100 µA
V
CHARGE
= 0V 0 0.1 µA
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
PACKAGE/ORDER I FOR ATIO
UUW
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ORDER PART NUMBER
LT3485EDD-0
LT3485EDD-1
LT3485EDD-2
LT3485EDD-3
T
JMAX
= 125°C θ
JA
= 43°C/W
EXPOSED PAD (11) IS GND, MUST BE SOLDERED TO PCB
TOP VIEW
11
DD PACKAGE
10-LEAD (3mm
´
3mm) PLASTIC DFN
10
9
6
7
8
4
5
3
2
1VMONT
DONE
IGBTPWR
IGBTIN
IGBTOUT
CHARGE
VBAT
VIN
SW
SW
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/
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
3
34850123fb
PARAMETER CONDITIONS MIN TYP MAX UNITS
Switch Leakage Current V
IN
= V
SW
= 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 100kΩ from V
IN
to DONE 3 V
DONE Output Signal Low 33µA into DONE Pin 140 200 mV
DONE Leakage Current V
DONE
= 3V, DONE NPN Off 20 100 nA
IGBT Input Voltage High ●1.5 V
IGBT Input Voltage Low ●0.3 V
IGBT Output Rise Time C
OUT
= 4000pF, IGBTPWR = 5V, 10%→90% 450 ns
IGBT Output Fall Time C
OUT
= 4000pF, IGBTPWR = 5V, 90%→10% 340 ns
V
OUT
Monitor Accuracy SW – V
BAT
= 20V 610 625 640 mV
SW – V
BAT
= 30V 920 940 960 mV
Monitor Output Current 200 µA
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
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.
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.
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
4
34850123fb
TYPICAL PERFOR A CE CHARACTERISTICS
UW
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 Input Current LT3485-2 Input Current LT3485-3 Input Current
LT3485-0 Input Current
LT3485-1 Charging Waveform
LT3485-0 Charging Waveform LT3485-2 Charging Waveform
LT3485-3 Charging Waveform Charge Time
VOUT
50V/DIV
0.5s/DIVVIN = 3.6V
COUT = 50µF
3485 G01
AVERAGE
INPUT
CURRENT
1A/DIV
VOUT
50V/DIV
0.5s/DIVVIN = 3.6V
COUT = 50µF
3485 G02
AVERAGE
INPUT
CURRENT
0.5A/DIV
VOUT
50V/DIV
0.5s/DIVVIN = 3.6V
COUT = 50µF
3485 G03
AVERAGE
INPUT
CURRENT
0.5A/DIV
V
OUT
50V/DIV
0.5s/DIVV
IN
= 3.6V
C
OUT
= 50µF
3485 G04
AVERAGE
INPUT
CURRENT
1A/DIV
VIN (V)
2
0
CHARGE TIME (SECONDS)
1
2
3
4
6
3456
1635 G05
78
5
LT3485-1
LT3485-3
LT3485-2
LT3485-0
COUT = 50µF
VOUT (V)
0
INPUT CURRENT (mA)
400
500
600
150 250
3485 G06
300
200
50 100 200 300
100
0
2.5V
3.6V
4.2V
VOUT (V)
050
0
INPUT CURRENT (mA)
100
250
100 200 250
3485 G07
50
200
150
150 300
2.5V
3.6V
4.2V
V
OUT
(V)
0
0
INPUT CURRENT (mA)
100
200
300
400
50 100 150 200
3485 G08
250 300
2.5V
3.6V
4.2V
VOUT (V)
0
0
INPUT CURRENT (mA)
100
300
400
500
200
900
3485 G09
200
100
50 250 300
150
600
700
800
2.5V
3.6V
4.2V
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
5
34850123fb
LT3485-1 Output Voltage
LT3485-0 Output Voltage
LT3485-3 Efficiency
LT3485-0 Efficiency LT3485-1 Efficiency LT3485-2 Efficiency
LT3485-2 Output Voltage LT3485 Switch Current Limits
LT3485-3 Output Voltage
V
OUT
(V)
50
40
EFFICIENCY (%)
50
60
70
80
90
100 150 200 250
3485 G10
300
2.5V
3.6V
4.2V
VOUT (V)
50
40
EFFICIENCY (%)
50
60
70
80
90
100 150 200 250
3485 G11
300
2.5V
3.6V
4.2V
VOUT (V)
50
40
EFFICIENCY (%)
50
60
70
80
90
100 150 200 250
3485 G12
300
2.5V
3.6V
4.2V
VOUT (V)
50
40
EFFICIENCY (%)
50
60
70
80
90
100 150 200 250
3485 G13
300
2.5V
3.6V
4.2V
V
IN
(V)
2
317
V
OUT
(V)
318
319
320
321
322
3456
3485 G14
78
–40°C
25°C
85°C
VIN (V)
2
317
VOUT (V)
318
319
320
321
322
3456
3485 G15
78
–40°C
25°C
85°C
VIN (V)
2
322
VOUT (V)
323
324
325
326
328
327
3456
3485 G16
78
–40°C
25°C
85°C
VIN (V)
2
317
VOUT (V)
318
319
320
321
322
3456
3485 G17
78
–40°C
25°C
85°C
TEMPERATURE (°C)
–40 –20
0
CURRENT LIMIT (mA)
800
2000
040 60
3485 G18
400
1600
1200
20 80 100
LT3485-3
LT3485-0
LT3485-2
LT3485-1
TYPICAL PERFOR A CE CHARACTERISTICS
UW
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/LT3485-1/
LT3485-2/LT3485-3
6
34850123fb
LT3485-1 Switching Waveform
LT3485-2 Switching Waveform LT3485-3 Switching Waveform
LT3485-0 Switching Waveform
LT3485-3 Switching Waveform
LT3485-2 Switching Waveform
LT3485-1 Switching Waveform
LT3485-0/LT3485-1/LT3485-2/
LT3485-3 Switch Breakdown
Voltage
LT3485-0 Switching Waveform
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 100V
3485 G19
IPRI
1A/DIV
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 100V
3485 G20
IPRI
1A/DIV
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 100V
3485 G21
IPRI
1A/DIV
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 300V
3485 G23
IPRI
1A/DIV
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 300V
3485 G24
IPRI
1A/DIV
VSW
10V/DIV
1µs/DIVVIN = 3.6V
VOUT = 300V
3485 G25
IPRI
1A/DIV
V
SW
10V/DIV
1µs/DIV 3485 G26
I
PRI
2A/DIV
V
IN
= 3.6V
V
OUT
= 300V
SWITCH VOLTAGE (V)
0 102030405060708090100
SWITCH CURRENT (mA)
3485 G27
10
9
8
7
6
5
4
3
2
1
0
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 PART
V
IN
= V
CHARGE
= 5V
TYPICAL PERFOR A CE CHARACTERISTICS
UW
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.
V
SW
10V/DIV
1µs/DIV 3485 G22
I
PRI
2A/DIV
V
IN
= 3.6V
V
OUT
= 100V
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
7
34850123fb
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.
V
BAT
(Pin 2): Battery Supply Pin. Must be locally bypassed
with a good quality ceramic capacitor. Battery supply
must be 1.7V or higher.
V
IN
(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:
NVOUT
=+2
31 5.
where V
OUT
is the desired output voltage.
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.
V
MONT
(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.
UU
U
PI FU CTIO S
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
8
34850123fb
TO BATTERY
C1
C2
R1
2.5k
R3
4k
ENABLE
1.25V
REFERENCE
LT3485-3: R
SENSE
= 0.010Ω
LT3485-0: R
SENSE
= 0.015Ω
LT3485-2: R
SENSE
= 0.022Ω
LT3485-1: R
SENSE
= 0.030Ω
SAMPLE
AND HOLD
CHIP
POWER
V
MONT
SW
4, 5
CHARGE
PRIMARY
R4
120k
R2
60k
T1 D1
SECONDARY
V
OUT
C
OUT
PHOTOFLASH
CAPACITOR
3485 F01
–
+
–
+
A2
V
OUT
COMPARATOR
DCM
COMPARATOR
45mV
20mV
DRIVER
IGBT
DRIVER
R
SENSE
GND
Q1
DONE
QQ
Q3
Q2
SR
ONE-
SHOT
ONE-
SHOT
IGBT
DRIVER
POWER
TO GATE OF IGBT
TO V
IN
TO V
IN
IGBTIN
+
–
A3
ONE-
SHOT
–
+
A1
S
RQ
+–
9 10 3 2
11
1
8
7
6
20Ω
20k
FU CTIO AL BLOCK DIAGRA
UU
W
Figure 1
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
9
34850123fb
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
V
OUT
no longer rises. When CHARGE is brought high
again, charging resumes. When the target V
OUT
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 V
MONT
pin functions as an output to a
microcontroller to communicate the progress of the charge.
The V
MONT
pin starts to function at about 0.2V, which
corresponds to 64V with a turns ratio of 10.2. When the
V
MONT
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.
OPERATIO
U
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 45mV higher than V
BAT
for this to happen.
During this phase, current is delivered to the photoflash
capacitor via the secondary and diode D1. As the second-
ary current decreases to zero, the SW pin voltage will begin
to collapse. When the SW pin voltage drops to 45mV above
V
BAT
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 (V
OUT
Comparator). Resistors R1 and
R2 are sized so that when the SW voltage is 31.5V above
V
BAT
, 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
LT3485-2
V
IN
= 3.6V
C
OUT
= 50µF
V
OUT
100V/DIV
V
CHARGE
5V/DIV
V
DONE
5V/DIV
1s/DIV
3485 F02
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
10
34850123fb
APPLICATIO S I FOR ATIO
WUUU
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/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 V
BAT
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:
NV
OUT
=+2
31 5.
where V
OUT
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, L
PRI
. Choose L
PRI
according to the following
formula:
LV
NI
PRI OUT
PK
≥
−
••
•
200 10
9
where V
OUT
is the desired output voltage. N is the trans-
former turns ratio. I
PK
is 1.4 (LT3485-0), 0.7 (LT3485-1),
1 (LT3485-2) and 2 (LT3485-3).
L
PRI
needs to be equal or larger than this value to ensure
that the LT3485-0/LT3485-1/LT3485-2/LT3485-3 has ad-
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-
tant 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 pri-
mary 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).
Table 1. Recommended Transformer Parameters
TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE
PARAMETER NAME LT3485-0 LT3485-1 LT3485-2 LT3485-3 UNITS
L
PRI
Primary Inductance >5 >10 >7 >3.5 µH
L
LEAK
Primary Leakage Inductance 100 to 300 200 to 500 200 to 500 100 to 300 nH
N Secondary: Primary Turns Ratio 8 to 12 8 to 12 8 to 12 8 to 12
V
ISO
Secondary to Primary Isolation Voltage >500 >500 >500 >500 V
I
SAT
Primary Saturation Current >1.6 >0.8 >1.0 >2 A
R
PRI
Primary Winding Resistance <300 <500 <400 <200 mΩ
R
SEC
Secondary Winding Resistance <40 <80 <60 <30 Ω
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
11
34850123fb
Note that the absolute maximum rating of the SW pin is
not ex
ceeded. Make sure to check the SW voltage wave-
form with V
OUT
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 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.
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 rat-
ings. The peak reverse voltage that the diode(s) will see is
approximately:
VVNV
PK R OUT IN−
=+(• )
APPLICATIO S I FOR ATIO
WUUU
Table 2. Pre-Designed Transformers – Typical Specifications Unless Otherwise Noted
TRANSFORMER SIZE L
PRI LPRI-LEAKAGE
R
PRI
R
SEC
FOR USE WITH NAME (W × L × H) mm (µH) (nH) N (mΩ)(Ω) VENDOR
LT3485-0/LT3485-2 SBL-5.6-1 5.6 × 8.5 × 4.0 10 200 Max 10.2 103 26 Kijima Musen
LT3485-1 SBL-5.6S-1 5.6 × 8.5 × 3.0 24 400 Max 10.2 305 55 Hong Kong Office
852-2489-8266 (ph)
kijimahk@netvigator.com (email)
LT3485-0 LDT565630T-001 5.8 × 5.8 × 3.0 6 200 Max 10.4 100 Max 10 Max TDK
LT3485-1 LDT565630T-002 5.8 × 5.8 × 3.0 14.5 500 Max 10.2 240 Max 16.5 Max Chicago Sales Office
LT3485-2 LDT565630T-003 5.8 × 5.8 × 3.0 10.5 550 Max 10.2 210 Max 14 Max (847) 803-6100 (ph)
LT3485-3 LDT565630T-041 5.8 × 5.8 × 3.0 4.7 150 Max 10.4 90 Max 6.4 Max www.components.tdk.com
LT3485-0/LT3485-1 T-15-089 6.4 × 7.7 × 4.0 12 400 Max 10.2 211 Max 27 Max Tokyo Coil Engineering
LT3485-1 T-15-083 8.0 × 8.9 × 2.0 20 500 Max 10.2 675 Max 35 Max Japan Office
LT3485-3 T-17-109A 6.5 × 7.9 × 4.0 5.9 300 Max 10.2 78 Max 18.61 Max 0426-56-6262 (ph)
www.tokyo-coil.co.jp
Figure 4. New Transformer Design Check (Not to Scale)
Figure 3. LT3485 SW Voltage Waveform
IPRI
1A/DIV
VSW
10A/DIV
VIN = 5V
VOUT = 320V
100ns/DIV
3485 F03
2
V
SW
3485 F04
0V
“A”
“B”
MUST BE
LESS THAN 40V
MUST BE
LESS THAN 50V
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
12
34850123fb
APPLICATIO S I FOR ATIO
WUUU
The peak current of the diode is simply:
I=
2
NLT3485-3
I=
1.4
NLT3485-0
PK-SEC
PK-SEC
()
())
()
I=
1
NLT3485-2
I=
0.7
NLT3485-
PK-SEC
PK-SEC 11
()
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
number of diodes to achieve the necessary reverse break-
down voltage.
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,
Table 3. Recommended Output Diodes
MAX REVERSE VOLTAGE MAX FORWARD CONTINUOUS CURRENT CAPACITANCE
PART (V) (mA) (pF) VENDOR
GSD2004S 2x300 225 5 Vishay
(Dual Diode) (402) 563-6866
www.vishay.com
BAV23S 2x250 225 5 Philips Semiconductor
(Dual Diode) (800) 234-7381
www.philips.com
MMBD3004S 2x350 225 5 Diodes Inc
(Dual Diode) (816) 251-8800
www.diodes.com
Figure 5. Complete Xenon Circuit
LT3485-0
IGBTOUT
IGBTIN
VIN
IGBTPWR
GND
VMONT
VBAT SW
4.7µF
1:10.2
•
•
VBAT
2 AA OR
1 TO 2 Li-Ion
0.22µF
VCC
5V
320V
TO
MICRO
1
T
C
A
23
1
2
4
5
3485 F05
150µF
PHOTOFLASH
CAPACITOR
2.2µF
600V
1M
CHARGE
DONE TRIGGER FLASHLAMP
IGBT
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
13
34850123fb
APPLICATIO S I FOR ATIO
WUUU
Table 4. Recommended IGBTs
DRIVE BREAKDOWN COLLECTOR
VOLTAGE VOLTAGE CURRENT
PART (V) (V) (PULSED) (A) VENDOR
CY25BAH-8F 2.5 400 150 Renesas
CY25BAJ-8F 4 400 150 (408) 382-7500
www.renesas.com
GT8G133 4 400 150 Toshiba Semiconductor
(949) 623-2900
www.semicon.toshiba.co.jp/eng/
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%
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 0.1µA.
Table 4 is a list of recommended IGBT devices for strobe
applications. These three devices are all packaged in
8-lead TSSOP packages.
V
OUT
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 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.)
GATE
EMITTER
3485 F06
Figure 6. IGBT Gate
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
14
34850123fb
APPLICATIO S I FOR ATIO
WUUU
Figure 7. Suggested Layout: Keep Electrical Path Formed by C1,
Transformer Primary and LT3485-0/LT3485-1/LT3485-2/LT3485-3 Short
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 com-
ponent 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
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 overvolt-
age condition on the SW pin.
COUT
PHOTOFLASH
CAPACITOR
CHARGE
DONE
IGBTPWR
VBAT
C2 C3
T1
C1
VMONT
IGBTIN
IGBTOUT
D1
(DUAL DIODE)
+
SECONDARY PRIMARY
VIN
•
•
1 10
92
R1
3485 F07
3811
74
56
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
15
34850123fb
Figure 8. LT3485-0 Photoflash Charger Uses High Efficiency 4mm Tall Transformer
Figure 9. LT3485-1 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
TYPICAL APPLICATIO S
U
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F08
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L
PRI
= 10µH, N = 10.2
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
V
MONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-0
GND
V
BAT
SW
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F09
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6S-1, L
PRI
= 24µH, N = 10.2
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
V
MONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-1
GND
V
BAT
SW
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
16
34850123fb
Figure 11. LT3485-3 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
Figure 10. LT3485-2 Photoflash Charger Uses High Efficiency 4mm Tall Transformer
TYPICAL APPLICATIO S
U
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F10
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L
PRI
= 10µH, N = 10.2
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
VMONT TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-2
GND
V
BAT
SW
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F11
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-041, L
PRI
= 4.7µH, N = 10.4
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
V
MONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-3
GND
V
BAT
SW
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
17
34850123fb
TYPICAL APPLICATIO S
U
Figure 12. LT3485-0 Photoflash Circuit Uses Tiny 3mm Tall Transformer
Figure 13. Charge Time with TDK Transformers (Figures 11, 12, 13, 14 and 15)
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F12
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-001, L
PRI
= 6µH, N = 10.4
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
V
MONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-0
GND
V
BAT
SW
VIN (V)
2
0
CHARGE TIME (SECONDS)
1
2
3
4
6
3456
3485 F13
78
5
LT3485-3
LT3485-0
LT3485-1
COUT = 50µF
LT3485-2
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
18
34850123fb
Figure 14. LT3485-1 Photoflash Circuit Uses Tiny 3mm Tall Transformer
Figure 15. LT3485-2 Photoflash Circuit Uses Tiny 3mm Tall Transformer
TYPICAL APPLICATIO S
U
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F14
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-002, L
PRI
= 14.5µH, N = 10.2
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
VMONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-1
GND
V
BAT
SW
C2
0.22µF
V
IN
2.5V TO 8V
DONE
CHARGE
C1
4.7µF
T1
1:10.2
VBAT
1.8V TO 8V 320V
3485 F15
C
OUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-003, L
PRI
= 10µH, N = 10.2
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
CHARGE
V
IN
VMONT
TO MICRO
TO GATE OF IGBT
IGBTOUT
IGBTPWR
IGBTIN
DONE
LT3485-2
GND
V
BAT
SW
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
19
34850123fb
3.00 ±0.10
(4 SIDES)
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
0.38 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
2.38 ±0.10
(2 SIDES)
15
106
PIN 1
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DD10) DFN 1005
0.25 ± 0.05
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65 ±0.05
(2 SIDES)2.15 ±0.05
0.50
BSC
0.675 ±0.05
3.50 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
U
PACKAGE DESCRIPTIO
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
20
34850123fb
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, V
OUT(MIN)
= 0.6V, I
Q
= 40µA,
Converter I
SD
<1µA, MS10E
LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Chargers with Charges 220µF to 320V in 3.7 seconds from 5V,
Automatic Top-Off V
IN
: 2.2V to 16V, I
Q
= 90µA, I
SD
< 1µA, MS10
LTC3425 5A I
SW
, 8MHz, Multi-Phase Synchronous Step-Up DC/DC 95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MIN)
= 5.25V, I
Q
= 12µA,
Converter I
SD
< 1µA, QFN-32
LTC3440 600mA/1A (I
OUT
), Synchronous Buck-Boost DC/DC 95% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
= 2.5V to 5.5V,
Converter I
Q
= 25µA, I
SD
< 1µA, MS-10 DFN-12
LT3468/LT3468-1/ Photoflash Capacitors in ThinSOT™ Charges 110µF to 320V in 4.6 Seconds from 3.6V,
LT3468-2 V
IN
: 2.5V to 16V, I
Q
= 5mA, I
SD
< 1µA, ThinSOT
LT3472 Dual ±34V, 1.2MHz Boost (350mA)/Inverting (400mA) Integrated Schottkys, V
IN
: 2.2V to 16V, V
OUT(MAX)
= ±34V,
DC/DC Converter for CCD Bias I
Q
= 2.5mA, I
SD
< 1µA, DFN
LT3463/LT3463A Dual Boost (250mA)/Inverting (250mA/400mA) Integrated Schottkys, V
IN
: 2.3V to 15V, V
OUT(MAX)
= ±40V,
DC/DC Converter for CCD Bias I
Q
= 40µA, I
SD
< 1µA, DFN
LT3484-0/LT3484-1/ Photoflash Capacitor Chargers Charges 110µF to 320V in 4.6 Seconds from 3.6V,
LT3484-2 V
IN
: 2.5V to 16V, V
BAT
: 1.8V to 16V, I
Q
= 5mA, I
SD
< 1µA,
2mm × 3mm DFN
ThinSOT is a trademark of Linear Technology Corporation.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
LT 0406 REV B • PRINTED IN USA
