LINER LT3485-2 Photoflash capacitor chargers with output voltage monitor and integrated igbt drive Datasheet

LT3485-0/LT3485-1/
LT3485-2/LT3485-3
Photoflash Capacitor
Chargers with Output Voltage
Monitor and Integrated IGBT Drive
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DESCRIPTIO
FEATURES
The LT®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.
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
■
■
■
■
■
■
■
■
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*
VIN = VBAT = 3.6V
100µF capacitor, 320V. *50µF capacitor
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APPLICATIO S
■
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.
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.
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TYPICAL APPLICATIO
LT3485-0 Photoflash Charger Uses High Efficiency 3mm Tall Transformers
DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
VBAT
2 AA OR
1 TO 2 Li-Ion
•
4
4.7µF
2
•
1M
5
150µF
PHOTOFLASH
CAPACITOR
SW
VBAT
LT3485-0 Charging Waveform
320V
1:10.2
1
DONE
TRIGGER T
1
CHARGE
GND
2
LT3485-0
VCC
5V
VIN
0.22µF
VMONT
IGBTPWR
IGBTIN
A
2.2µF
600V
FLASHLAMP
VOUT
50V/DIV
3
TO
MICRO
C
IGBT
IGBTOUT
AVERAGE
INPUT CURRENT
0.5A/DIV
VIN = 3.6V
COUT = 100µF
1s/DIV
3485 TA02
3485 TA01
34850123fb
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
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 .......................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
TOP VIEW
10 VMONT
CHARGE
1
VBAT
2
VIN
3
SW
4
7 IGBTIN
SW
5
6 IGBTOUT
9 DONE
11
8 IGBTPWR
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
ORDER PART NUMBER
DD PART MARKING
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 TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
PARAMETER
Quiescent Current
CONDITIONS
Not Switching
VCHARGE = 0V
MIN
TYP
5
0
MAX
8
1
10
31
1.7
1.2
0.85
0.55
310
210
170
100
31.5
1.8
1.3
0.95
0.65
400
300
225
175
32
A
A
A
A
mV
mV
mV
mV
V
10
200
45
400
120
mV
mV
65
0
100
0.1
µA
µA
VIN Voltage Range
●
2.5
VBAT Voltage Range
●
1.7
Switch Current Limit
VOUT Comparator Trip Voltage
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
VOUT Comparator Overdrive
DCM Comparator Trip Voltage
300ns Pulse Width
Measured as VSW – VIN
CHARGE Pin Current
VCHARGE = 3V
VCHARGE = 0V
Switch VCESAT
1.6
1.1
0.75
0.45
●
●
10
UNITS
mA
µA
V
V
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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 TA = 25°C. VIN = VBAT = VCHARGE = 3V, unless otherwise noted.
PARAMETER
Switch Leakage Current
CONDITIONS
VIN = VSW = 5V, in Shutdown
TYP
0.01
100kΩ from VIN to DONE
DONE Output Signal Low
33µA into DONE Pin
DONE Leakage Current
VDONE = 3V, DONE NPN Off
3
●
IGBT Input Voltage High
COUT = 4000pF, IGBTPWR = 5V, 10%→90%
COUT = 4000pF, IGBTPWR = 5V, 90%→10%
SW – VBAT = 20V
SW – VBAT = 30V
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.
V
140
200
mV
20
100
nA
1.5
V
●
IGBT Input Voltage Low
0.3
610
920
V
µs
20
DONE Output Signal High
UNITS
µA
V
0.3
High→Low→High
Monitor Output Current
MAX
1
1
●
CHARGE Input Voltage Low
IGBT Output Rise Time
IGBT Output Fall Time
VOUT Monitor Accuracy
●
●
CHARGE Input Voltage High
Minimum Charge Pin Low Time
MIN
450
340
625
940
200
640
960
V
ns
ns
mV
mV
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.
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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
LT3485-0 Charging Waveform
VOUT
50V/DIV
LT3485-2 Charging Waveform
VOUT
50V/DIV
VOUT
50V/DIV
AVERAGE
INPUT
CURRENT
1A/DIV VIN = 3.6V
COUT = 50µF
3485 G01
0.5s/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV VIN = 3.6V
COUT = 50µF
LT3485-3 Charging Waveform
3485 G02
0.5s/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV V = 3.6V
IN
COUT = 50µF
LT3485-0 Input Current
Charge Time
6
600
COUT = 50µF
LT3485-1
CHARGE TIME (SECONDS)
5
AVERAGE
INPUT
CURRENT
1A/DIV V = 3.6V
IN
COUT = 50µF
4
3
2
1
3485 G04
0.5s/DIV
500
LT3485-2
INPUT CURRENT (mA)
VOUT
50V/DIV
400
300
200
2.5V
3.6V
4.2V
100
LT3485-0
0
3485 G03
0.5s/DIV
2
3
4
LT3485-3
5
VIN (V)
7
6
0
8
0
50
100
150 200
VOUT (V)
250
1635 G05
LT3485-1 Input Current
3485 G06
LT3485-2 Input Current
250
300
LT3485-3 Input Current
400
900
800
150
100
50
2.5V
3.6V
4.2V
0
0
50
100
150 200
VOUT (V)
250
300
3485 G07
700
300
INPUT CURRENT (mA)
INPUT CURRENT (mA)
INPUT CURRENT (mA)
200
200
100
2.5V
3.6V
4.2V
0
0
50
100
150 200
VOUT (V)
250
300
3485 G08
600
500
400
300
200
2.5V
3.6V
4.2V
100
0
0
50
100
150 200
VOUT (V)
250
300
3485 G09
34850123fb
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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 Efficiency
LT3485-2 Efficiency
90
80
80
80
70
60
50
40
70
60
50
2.5V
3.6V
4.2V
40
50
100
150
200
VOUT (V)
250
EFFICIENCY (%)
90
EFFICIENCY (%)
EFFICIENCY (%)
LT3485-0 Efficiency
90
300
100
150
200
VOUT (V)
250
LT3485-0 Output Voltage
321
321
70
320
320
100
150
200
VOUT (V)
250
319
318
2.5V
3.6V
4.2V
50
VOUT (V)
80
VOUT (V)
322
40
150
200
VOUT (V)
250
300
317
300
2
3
4
5
VIN (V)
6
7
319
318
–40°C
25°C
85°C
3485 G13
317
8
–40°C
25°C
85°C
2
3
4
5
VIN (V)
6
7
3485 G14
LT3485-2 Output Voltage
8
3485 G15
LT3485 Switch Current Limits
LT3485-3 Output Voltage
328
322
2000
321
1600
VOUT (V)
–40°C
25°C
85°C
326
325
CURRENT LIMIT (mA)
LT3485-3
327
319
318
323
317
2
3
4
5
VIN (V)
6
7
8
3485 G16
LT3485-0
1200
320
324
322
100
LT3485-1 Output Voltage
322
50
50
3485 G12
90
60
2.5V
3.6V
4.2V
3485 G11
LT3485-3 Efficiency
EFFICIENCY (%)
40
300
3485 G10
VOUT (V)
60
50
2.5V
3.6V
4.2V
50
70
3
4
5
VIN (V)
6
7
800
LT3485-1
400
–40°C
25°C
85°C
2
LT3485-2
8
3485 G17
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
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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
VSW
10V/DIV
VSW
10V/DIV
IPRI
1A/DIV
IPRI
1A/DIV
VIN = 3.6V
VOUT = 100V
1µs/DIV
3485 G19
VSW
10V/DIV
IPRI
2A/DIV
VIN = 3.6V
VOUT = 100V
1µs/DIV
VSW
10V/DIV
IPRI
1A/DIV
VIN = 3.6V
VOUT = 100V
LT3485-3 Switching Waveform
LT3485-2 Switching Waveform
3485 G20
1µs/DIV
VIN = 3.6V
VOUT = 100V
3485 G21
1µs/DIV
LT3485-1 Switching Waveform
LT3485-0 Switching Waveform
VSW
10V/DIV
VSW
10V/DIV
IPRI
1A/DIV
IPRI
1A/DIV
3485 G22
VIN = 3.6V
VOUT = 300V
LT3485-2 Switching Waveform
3485 G23
1µs/DIV
VIN = 3.6V
VOUT = 300V
3485 G24
1µs/DIV
LT3485-0/LT3485-1/LT3485-2/
LT3485-3 Switch Breakdown
Voltage
LT3485-3 Switching Waveform
VSW
10V/DIV
VSW
10V/DIV
IPRI
2A/DIV
IPRI
1A/DIV
VIN = 3.6V
VOUT = 300V
1µs/DIV
3485 G25
VIN = 3.6V
VOUT = 300V
1µs/DIV
3485 G26
SWITCH CURRENT (mA)
10
SW PIN IS RESISTIVE UNTIL BREAKDOWN
9 VOLTAGE DUE TO INTEGRATED
RESISTORS. THIS DOES NOT INCREASE
8 QUIESCENT CURRENT OF PART
7
T = 25°C
6
5
4
T = –40°C
T = 85°C
3
2
1
VIN = VCHARGE = 5V
0
0
10 20 30 40 50 60 70 80 90 100
SWITCH VOLTAGE (V)
3485 G27
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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. 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=
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.
VOUT + 2
31.5
where VOUT is the desired output voltage.
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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FU CTIO AL BLOCK DIAGRA
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PRIMARY
C1
U
TO VIN
C2
DONE
10
3
2
R2
60k
Q3
SAMPLE
AND HOLD
CHARGE
VOUT
SECONDARY
SW
4, 5
VMONT
9
D1
T1
TO BATTERY
Q
Q
S
R
CHIP
POWER
Q2
ENABLE
R3
4k
R1
2.5k
R4
120k
DCM
COMPARATOR
ONESHOT
COUT
PHOTOFLASH
CAPACITOR
+
A3
–
+
–
1
ONESHOT
8
IGBT
DRIVER
POWER
45mV
+
A2
TO VIN
IGBTIN
VOUT
COMPARATOR
–
1.25V
REFERENCE
DRIVER
7
R
IGBT
DRIVER
S
Q
Q1
20Ω
+
20k
ONESHOT
RSENSE
A1
– +–
GND
11
20mV
6
3485 F01
TO GATE OF IGBT
LT3485-3: RSENSE = 0.010Ω
LT3485-0: RSENSE = 0.015Ω
LT3485-2: RSENSE = 0.022Ω
LT3485-1: RSENSE = 0.030Ω
Figure 1
34850123fb
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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OPERATIO
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 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 45mV 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
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 = 50µF
1s/DIV
3485 F02
Figure 2. Halting the Charging Cycle with the CHARGE Pin
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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
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
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).
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
µH
nH
V
A
mΩ
Ω
34850123fb
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LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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.
Capacitor 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.
Output Diode Selection
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.
For the input bypass capacitors, high quality X5R or X7R
types should be used. Make sure the voltage capability of
the part is adequate.
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”
IPRI
1A/DIV
2
“A”
MUST BE
LESS THAN 40V
VSW
VSW
10A/DIV
MUST BE
LESS THAN 50V
0V
VIN = 5V
VOUT = 320V
100ns/DIV
3485 F03
3485 F04
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
SBL-5.6-1
SBL-5.6S-1
SIZE
(W × L × H) mm
5.6 × 8.5 × 4.0
5.6 × 8.5 × 3.0
LPRI
(µH)
10
24
LPRI-LEAKAGE
FOR USE WITH
LT3485-0/LT3485-2
LT3485-1
(nH)
200 Max
400 Max
N
10.2
10.2
RPRI
(mΩ)
103
305
RSEC
(Ω)
26
55
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
5.8 × 5.8 × 3.0
5.8 × 5.8 × 3.0
5.8 × 5.8 × 3.0
5.8 × 5.8 × 3.0
6.4 × 7.7 × 4.0
8.0 × 8.9 × 2.0
6.5 × 7.9 × 4.0
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)
[email protected] (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
34850123fb
11
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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The peak current of the diode is simply:
IGBT Drive
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
BAV23S dual silicon diodes. Table 3 shows the various
diodes and relevant specifications. Use the appropriate
number of diodes to achieve the necessary reverse breakdown voltage.
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 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
(V)
2x300
MAX FORWARD CONTINUOUS CURRENT
(mA)
225
CAPACITANCE
(pF)
5
BAV23S
(Dual Diode)
2x250
225
5
MMBD3004S
(Dual Diode)
2x350
225
5
PART
GSD2004S
(Dual Diode)
VBAT
2 AA OR
1 TO 2 Li-Ion
320V
1:10.2
1
•
4
4.7µF
2
•
1M
5
150µF
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
GND
2
LT3485-0
VIN
0.22µF
VMONT
IGBTPWR
IGBTIN
A
2.2µF
600V
TRIGGER T
1
CHARGE
VCC
5V
VENDOR
Vishay
(402) 563-6866
www.vishay.com
Philips Semiconductor
(800) 234-7381
www.philips.com
Diodes Inc
(816) 251-8800
www.diodes.com
FLASHLAMP
3
TO
MICRO
C
IGBT
IGBTOUT
3485 F05
Figure 5. Complete Xenon Circuit
34850123fb
12
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
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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 0.1µA.
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 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.)
Table 4. Recommended IGBTs
PART
CY25BAH-8F
CY25BAJ-8F
GT8G133
DRIVE
VOLTAGE
(V)
2.5
4
BREAKDOWN
VOLTAGE
(V)
400
400
COLLECTOR
CURRENT
(PULSED) (A)
150
150
4
400
150
VENDOR
Renesas
(408) 382-7500
www.renesas.com
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
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
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.
VMONT
CHARGE
R1
DONE
C2
10
2
9
C3
8
IGBTPWR
4
7
IGBTIN
5
6
3
+
COUT
PHOTOFLASH
CAPACITOR
VIN
1
11
IGBTOUT
•
T1
SECONDARY
3485 F07
PRIMARY
•
C1
D1
(DUAL DIODE)
VBAT
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
VBAT
1.8V TO 8V
T1
1:10.2
D1
320V
C1
4.7µF
R1
100k
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-0
VIN
2.5V TO 8V
VIN
C2
0.22µF
VMONT
IGBTPWR
TO MICRO
IGBTOUT
TO GATE OF IGBT
IGBTIN
3485 F08
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2
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
VBAT
1.8V TO 8V
T1
1:10.2
DONE
320V
C1
4.7µF
R1
100k
CHARGE
D1
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
GND
CHARGE
LT3485-1
VIN
2.5V TO 8V
C2
0.22µF
VIN
IGBTPWR
IGBTIN
VMONT
TO MICRO
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, LPRI = 24µH, N = 10.2
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
VBAT
1.8V TO 8V
T1
1:10.2
D1
320V
C1
4.7µF
R1
100k
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-2
VIN
2.5V TO 8V
VIN
C2
0.22µF
VMONT
IGBTPWR
TO MICRO
IGBTOUT
TO GATE OF IGBT
IGBTIN
3485 F10
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2
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
VBAT
1.8V TO 8V
T1
1:10.2
DONE
320V
C1
4.7µF
R1
100k
CHARGE
D1
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
GND
CHARGE
LT3485-3
VIN
2.5V TO 8V
VIN
C2
0.22µF
VMONT
IGBTPWR
TO MICRO
IGBTOUT
IGBTIN
TO GATE OF IGBT
3485 F11
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-041, LPRI = 4.7µH, N = 10.4
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
VBAT
1.8V TO 8V
D1
320V
C1
4.7µF
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-0
VIN
2.5V TO 8V
VIN
C2
0.22µF
VMONT
IGBTPWR
TO MICRO
IGBTOUT
TO GATE OF IGBT
IGBTIN
3485 F12
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-001, LPRI = 6µH, N = 10.4
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
COUT = 50µF
CHARGE TIME (SECONDS)
5
LT3485-1
4
LT3485-2
3
2
1
LT3485-0
0
2
3
LT3485-3
4
5
VIN (V)
6
7
8
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
VBAT
1.8V TO 8V
T1
1:10.2
D1
320V
C1
4.7µF
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
DONE
GND
CHARGE
CHARGE
LT3485-1
VIN
2.5V TO 8V
VIN
C2
0.22µF
VMONT
IGBTPWR
TO MICRO
IGBTOUT
TO GATE OF IGBT
IGBTIN
3485 F14
C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-002, LPRI = 14.5µH, N = 10.2
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
VBAT
1.8V TO 8V
T1
1:10.2
CHARGE
320V
C1
4.7µF
COUT
PHOTOFLASH
CAPACITOR
SW
VBAT
DONE
D1
DONE
GND
CHARGE
LT3485-2
VIN
2.5V TO 8V
VIN
C2
0.22µF
IGBTPWR
IGBTIN
VMONT
TO MICRO
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, LPRI = 10µH, N = 10.2
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
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
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
10
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1005
5
0.200 REF
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3407
Dual 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC
Converter
96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40µA,
ISD <1µA, MS10E
LT3420/LT3420-1
1.4A/1A, Photoflash Capacitor Chargers with
Automatic Top-Off
Charges 220µF to 320V in 3.7 seconds from 5V,
VIN: 2.2V to 16V, IQ = 90µA, ISD < 1µA, MS10
LTC3425
5A ISW, 8MHz, Multi-Phase Synchronous Step-Up DC/DC
Converter
95% Efficiency, VIN: 0.5V to 4.5V, VOUT(MIN) = 5.25V, IQ = 12µA,
ISD < 1µA, QFN-32
LTC3440
600mA/1A (IOUT), Synchronous Buck-Boost DC/DC
Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V to 5.5V,
IQ = 25µA, ISD < 1µA, MS-10 DFN-12
LT3468/LT3468-1/
LT3468-2
Photoflash Capacitors in ThinSOT™
Charges 110µF to 320V in 4.6 Seconds from 3.6V,
VIN: 2.5V to 16V, IQ = 5mA, ISD < 1µA, ThinSOT
LT3472
Dual ±34V, 1.2MHz Boost (350mA)/Inverting (400mA)
DC/DC Converter for CCD Bias
Integrated Schottkys, VIN: 2.2V to 16V, VOUT(MAX) = ±34V,
IQ = 2.5mA, ISD < 1µA, DFN
LT3463/LT3463A
Dual Boost (250mA)/Inverting (250mA/400mA)
DC/DC Converter for CCD Bias
Integrated Schottkys, VIN: 2.3V to 15V, VOUT(MAX) = ±40V,
IQ = 40µA, ISD < 1µA, DFN
LT3484-0/LT3484-1/
LT3484-2
Photoflash Capacitor Chargers
Charges 110µF to 320V in 4.6 Seconds from 3.6V,
VIN: 2.5V to 16V, VBAT: 1.8V to 16V, IQ = 5mA, ISD < 1µA,
2mm × 3mm DFN
ThinSOT is a trademark of Linear Technology Corporation.
34850123fb
20
Linear Technology Corporation
LT 0406 REV B • PRINTED IN USA
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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