Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - power management - special purpose 90 µA MSOP 10

LT3420/LT3420-1

3420fb

, LTC and LT are registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners. *Protected by U.S. Patents

including 6518733.

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

■

Digital Camera Flash Unit

■

Film Camera Flash Unit

■

High Voltage Power Supplies

■

Charges 220µF to 320V in 3.7 Seconds

from 5V (LT3420)

■

Charges 100µF to 320V in 3.5 Seconds

from 5V (LT3420-1)

■

Charges Any Size Photoflash Capacitor

■

Supports Operation from Two AA Cells or Any

Supply from 1.8V to 16V

■

Controlled Peak Switch Current: 1.4A (LT3420)

1.0A (LT3420-1)

■

Controlled Input Current: 840mA (LT3420)

450mA (LT3420-1)

■

Uses Standard Transformers

■

Efficient Flyback Operation (>75% Typical)

■

Adjustable Output

■

Automatic Refresh

■

Charge Complete Indicator

■

No High Voltage Zener Diode Required

■

No Output Voltage Divider Required

■

Small 10-Lead MSOP Package

■

Small 10-Lead (3mm × 3mm) DFN Package

Photoflash Capacitor

Chargers with Automatic Refresh

The LT

3420/LT3420-1 charge high voltage photoflash

capacitors quickly and efficiently. Designed for use in both

digital and film cameras, these devices use a flyback

topology to achieve efficiencies up to four times better

than competing flash modules. A unique adaptive off-time

control algorithm* maintains current-limited continuous

mode transformer operation throughout the entire charge

cycle, eliminating the high inrush current often found in

modules.

The LT3420/LT3420-1 output voltage sensing scheme*

monitors the flyback voltage to indirectly regulate the

output voltage, eliminating an output resistor divider or

discrete zener diode. This feature allows the capacitor to

be held at a fully charged state without excessive power

consumption. Automatic refresh (which can be defeated)

allows the capacitor to remain charged while consuming

an average input current of about 2mA, at a user-defined

refresh rate. A logic high on the CHARGE pin initiates

charging, while the DONE pin signals that the capacitor is

fully charged.

The LT3420/LT3420-1 are available in 10-Lead MSOP and

(3mm × 3mm) DFN packages.

Figure 1. High Charge Rate LT3420 Photoflash Circuit

BAT

1.8V TO 6V

INPUT CURRENT

≈350mA

3420 F01

CHARGE

DONE

SEC

REF

LT3420

BAT

GND

4.7µF

0.1µF

4.7µF

2.5V TO 10V

CHARGE

DONE

51.1k

1:12

320V

3,4

5,6

C1, C2: 4.7µF, X5R or X7R, 10V

C3: RUBYCON 220µF PHOTOFLASH CAPACITOR

T1: TDK SRW10EPC-U01H003 FLYBACK TRANSFORMER

D1: VISHAY GSD2004S SOT-23

DUAL DIODE. DIODES CONNECTED IN SERIES

220µF

330V

PHOTOFLASH

CAPACITOR

10 5

632

DANGER HIGH VOLTAGE

OPERATION BY HIGH VOLTAGE

TRAINED PERSONNEL ONLY

Figure 2. Small Size LT3420-1 Photoflash Circuit

3420 F02

CHARGE

DONE

SEC

REF

LT3420-1

BAT

GND

4.7µF

0.1µF

4.7µF

BAT

1.8V TO 6V

INPUT CURRENT

≈450mA

2.5V TO 6V

CHARGE

DONE

60.4k

1:10

(3mm TALL)

320V

C1, C2: 4.7µF, X5R or X7R, 6.3V

C3: RUBYCON 100µF PHOTOFLASH CAPACITOR

T1: KIJIMA MUSEN SBL-5.6S-2

D1: VISHAY GSD2004S SOT-23

DUAL DIODE. DIODES CONNECTED IN SERIES

100µF

330V

PHOTOFLASH

CAPACITOR

10 5

632

Summary of content (20 pages)

PAGE 1
LT3420/LT3420-1 Photoflash Capacitor Chargers with Automatic Refresh DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Charges 220µF to 320V in 3.7 Seconds from 5V (LT3420) Charges 100µF to 320V in 3.5 Seconds from 5V (LT3420-1) Charges Any Size Photoflash Capacitor Supports Operation from Two AA Cells or Any Supply from 1.8V to 16V Controlled Peak Switch Current: 1.4A (LT3420) 1.
PAGE 2
LT3420/LT3420-1 W W U W ABSOLUTE AXI U RATI GS (Note 1) VCC Voltage .............................................................. 16V VBAT Voltage ............................................................ 16V SW Voltage (Note 2) LT3420 ................................................................ 38V LT3420-1 ............................................................ 50V SEC Current ...................................................... ±200mA RFB Current ....................................
PAGE 3
LT3420/LT3420-1 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VBAT = 3.3V, VCHARGE = VCC unless otherwise noted. (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS Primary Side Current Limit LT3420 (Note 5) LT3420-1 (Note 5) 1.20 0.75 1.4 0.9 1.60 1.
PAGE 4
LT3420/LT3420-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Graphs apply to both the LT3420 and LT3420-1 unless otherwise noted. Output Voltage in Refresh Mode, LT3420-1 335 330 330 325 325 320 320 315 310 Charge Time, LT3420-1 10 315 310 305 305 FIGURE 2 CIRCUIT VCC = 3.3V VBAT = 3.3V 300 295 –50 –25 0 25 50 75 100 FIGURE 2 CIRCUIT VCC = VIN VBAT = VIN TA = 25°C 300 295 2.5 125 3.0 TEMPERATURE (°C) 3.5 4.0 4.5 5.0 5.5 6 COUT = 100µF 4 COUT = 40µF 2 0 6.
PAGE 5
LT3420/LT3420-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Graphs apply to both the LT3420 and LT3420-1 unless otherwise noted. Efficiency for Figure 2 Circuit, LT3420-1 AVERAGE INPUT CURRENT (mA) TA = 25°C 80 EFFICIENCY (%) Input Current, LT3420 1000 VIN = 5V VIN = 3.3V 70 60 50 VCC = VBAT = VIN 40 50 100 150 250 200 VOUT (V) 300 900 FIGURE 1 CIRCUIT VCC = VBAT = 3.
PAGE 6
LT3420/LT3420-1 U U U PI FU CTIO S RREF (Pin 1): Reference Resistor Pin. Place a resistor (R2) from the RREF pin to GND. 2k is recommended. VBAT (Pin 2): Battery Voltage Input. This pin should be connected to the power supply or battery, which supplies power to transformer T1. Must be locally bypassed. RFB (Pin 3): Feedback Resistor Pin. Place a resistor (R1) from the SW pin to the RFB pin. Set R1 according to the following formula: R2 R1 = [(1.
PAGE 7
LT3420/LT3420-1 W BLOCK DIAGRA S T1 1:12 VBAT VOUT D1 C1 SECONDARY PRIMARY R1 R2 DONE RFB VBAT 8 2 SW RREF 3 1 6 C4 PHOTOFLASH CAPACITOR D3 CT 10 REFRESH TIMER Q5 R Q3 S + Q1 Q DRIVER C3 + ENABLE Q + 1V REFERENCE – 4 A2 ONESHOT GND 0.25Ω +– 7 SEC POWER DELIVERY BLOCK CHIP ENABLE VCC 5 10mV + VCC 9 +– Q4 R A3 CHARGE 0.014Ω 20mV – S MASTER LATCH A1 – Q ONESHOT Q2 BLOCK ENABLE LT3420 C2 3420 F03 Figure 3.
PAGE 8
LT3420/LT3420-1 U OPERATIO Overview The following text focuses on the operation of the LT3420. The operation of the LT3420-1 is nearly identical with the differences discussed at the end of this section. The LT3420 uses an adaptive on-time/off-time control scheme to provide excellent efficiency and precise control of switching currents. Please refer to Figure 3 for the following overview of the part’s operation.
PAGE 9
LT3420/LT3420-1 U OPERATIO ISW 1A/DIV ISW 1A/DIV ISEC 200mA/DIV ISEC 200mA/DIV VSW 20V/DIV VSW 20V/DIV 2µs/DIV 3420 F06a Figure 6a. Switching Waveforms with VOUT = 100V, VCC = VBAT = 3.3V of Q1 so that the peak current of Q1 is 1.4A and the minimum secondary current is 40mA (typical values). The previously described charging cycle must be halted when the output voltage reaches the desired value. The LT3420 monitors the output voltage via the flyback pulse on the SW pin.
PAGE 10
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION Transformer Primary Inductance Choosing the Right Transformer A flyback transformer needs to store substantial amounts of energy in the core during each switching cycle. The transformer, therefore, will generally require an air gap. The use of an air gap in the core makes the energy storage ability, or inductance, much more stable with temperature and variations in the core material.
PAGE 11
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO must be taken into account for the dynamic blocking voltage capabilities of the LT3420/LT3420-1. The dynamic blocking voltage capability of both parts is 38V. Table 1 summarizes the various breakdown voltages of the SW pin for both parts. Table 1.
PAGE 12
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO efficiency of the circuit. In addition, the effective capacitance on the primary is largely dominated by the actual secondary capacitance. This is simply a result of any secondary capacitance being multiplied by N2 when reflected to the primary. Since N is generally 10 or higher, a small capacitance of 10pF on the secondary is 100 times larger, or 1.0nF, on the primary.
PAGE 13
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO CAPACITOR SELECTION The VBAT and VCC decoupling capacitors should be multilayer ceramic type with X5R or X7R dielectric. This insures adequate decoupling across wide ambient temperature ranges. A good quality ceramic capacitor is also recommended for the timing capacitor on the CT pin. Avoid Y5V or Z5U dielectrics. Selectively Disabling the LT3420/LT3420-1 The LT3420/LT3420-1 can be disabled at any time, even during the charge phase.
PAGE 14
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO risk of drawing too much current from the battery. The input current to the LT3420/LT3420-1 circuit can be adjusted by driving the CHARGE pin with a PWM (pulse width modulation) signal. The microprocessor can adjust the duty cycle of the PWM signal to achieve the desired level of input current. Many schemes exist to achieve this function.
PAGE 15
LT3420/LT3420-1 U W U U APPLICATIO S I FOR ATIO BOARD LAYOUT The high voltage operation of the LT3420/LT3420-1 demands careful attention to board layout. You will not get advertised performance with careless layout. Figures 11 and 12 show the recommended component placement. Keep the area for the high voltage end of the secondary as small as possible. Note the larger than minimum spacing for all high voltage nodes. This is necessary to meet the breakdown specifications for the circuit board.
PAGE 16
LT3420/LT3420-1 U TYPICAL APPLICATIO S Professional Charger uses Multiple LT3420 Circuits in Parallel to Charge Large Photoflash Capacitors Quickly D1 VBAT 1.8V TO 6V 5, 6 C1 4.7µF 2 VBAT VCC 2.5V TO 10V CHARGE R1 52.3k 3 RFB + T1 1:12 3, 4 DANGER HIGH VOLTAGE OPERATION BY HIGH VOLTAGE TRAINED PERSONEL ONLY 320V 8 1 650µF* 350V PHOTOFLASH CAPACITOR 6 SW 4 VCC SEC 7 C2 MASTER 4.7µF LT3420 CHARGER 9 CHARGE 1 8 RREF DONE GND CT R2 2k 10 5 C3 0.1µF D2 VBAT C4 4.
PAGE 17
LT3420/LT3420-1 U TYPICAL APPLICATIO S LT3420 Photoflash Charging Circuit Uses Small Transformer DANGER HIGH VOLTAGE OPERATION BY HIGH VOLTAGE TRAINED PERSONEL ONLY VBAT 1.8V TO 5V C1 4.7µF T1* 1:12 2 4 VCC 2.5V TO 10V C2 4.7µF 9 CHARGE DONE 8 RFB VCC D1 5 R1 47.5k 3 2 VBAT 300V 3 1 6 SW 7 SEC LT3420 CHARGE DONE CT RREF 10 5 C4 220µF 330V PHOTOFLASH CAPACITOR + 1 GND C3 0.1µF R2 2k C1: 4.7µF, X5R or X7R, 6.3V C2: 4.
PAGE 18
LT3420/LT3420-1 U PACKAGE DESCRIPTIO MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.
PAGE 19
LT3420/LT3420-1 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) R = 0.115 TYP 6 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 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 1103 5 0.200 REF 1 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.00 – 0.05 2.38 ±0.
PAGE 20
LT3420/LT3420-1 U TYPICAL APPLICATIO LT3420-1 Photoflash Circuit Uses Tiny (3mm Tall) Transformer T1 1:10.2 VBAT 1.8V TO 6V C1 4.7µF VCC 2.5V TO 6V CHARGE DONE 8 1 2 3 RFB VCC C2 4.7µF 9 Charge Time 10 VOUT CHARGED FROM 50V TO 320V 8 6 SW C3 100µF 7 330V PHOTOFLASH CAPACITOR SEC LT3420-1 CHARGE 8 320V D1 60.4k VBAT 4 4 DONE CT RREF 10 5 + TIME (s) DANGER HIGH VOLTAGE OPERATION BY HIGH VOLTAGE TRAINED PERSONEL ONLY 5 COUT = 100µF 4 1 COUT = 40µF GND 0.