LT3750 - Capacitor Charger Controller
Document overview
- Manufacturer or author: Linear Technology Corporation
- PDF pages: 16
Technical content
■ Emergency Warning Beacons ■ Professional Photoflash Systems ■ Security/Inventory Control Systems ■ High Voltage Power Supply ■ Electric Fences ■ Detonators Capacitor Charger Controller ■ Charges Any Size Capacitor ■ Easily Adjustable Output Voltage ■ Drives High Current NMOS FETs ■ Primary-Side Sense—No Output Voltage Divider Necessary ■ Wide Input Range: 3V to 24V ■ Drives Gate to VCC – 2V ■ Available in 10-Lead MS Package FEATURES DESCRIPTIO U APPLICATIO SU TYPICAL APPLICATIO U , 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, 6636021. The LT 3750 is a flyback converter designed to rapidly charge large capacitors to a user-adjustable target volt- age. A patented boundary mode control scheme* mini- mizes transition losses and reduces transformer size. The transformer turns ratio and two external resistors easily adjust the output voltage.* A low 78mV current sense accurately limits peak switch current and also helps to maximize efficiency. With a wide input voltage range, the LT3750 can operate from a variety of power sources. A typical application can charge a 100µF capacitor to 300V in less than 300ms. The CHARGE pin gives full control of the LT3750 to the user. The DONE pin indicates when the capacitor has reached its programmed value and the part has stopped charging. VCC DONE CHARGE RVOUT RDCM GATE SOURCE VTRANS 60.4k 1:10 VOUT 300V VTRANS VCC 12V 100µF 43k 12mΩ
3750 TA01a
2.49k 100pF OFF ON 10µF 10µF 56µF ×2 + 300V, 6A Capacitor Charger TIME (SECONDS) VOUT (V) 100 150 200 250 300 0.1 0.2 0.3 0.4
3750 TA03c
0.5 VTRANS = 18V VTRANS = 6V VTRANS = 12V 6A Charge Time
PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum VCC ● 2.8 3 V Minimum VTRANS ● 2.5 3 V VCC Quiescent Current Not Switching, CHARGE = 5V 1.6 2.5 mA Not Switching, CHARGE = 0V 1 µA VTRANS Quiescent Current Not Switching, CHARGE = 5V 140 250 µA Not Switching, CHARGE = 0V 1 µA CHARGE Pin Current CHARGE = 24V 24 µA CHARGE = 5V 19 µA CHARGE = 0V 1 µA CHARGE Pin Enable Voltage ● 0.87 1.1 V CHARGE Pin Disable Voltage ● 0.2 0.6 V Minimum CHARGE Pin Low Time High →Low→High 20 µs VOUT Comparator Trip Voltage Measured RBG Pin ● 1.215 1.24 1.265 V VOUT Comparator Overdrive 1 µs Pulse Width, Measured on RBG Pin 30 mV RBG Pin Bias Current RBG = 1.2V 70 500 nA DCM Comparator Trip Voltage Measured as V DRAIN – VTRANS, RDCM = 43k (Note 3) ● 53 6 8 0 m V Current Limit Comparator Trip Voltage ● 68 78 88 mV DONE Output Signal High 100k Ω to 5V 4.9 5 V DONE Output Signal Low 100k Ω to 5V 0.1 0.2 V DONE Pin Leakage Current DONE = 2.5V 0.2 µA NMOS Minimum On Time 0.6 µs GATE Rise Time 50 ns GATE High Voltage C GATE = 1nF, VCC = 5V 3 3.8 4.5 V CGATE = 1nF, VCC = 24V 22 22.6 23.5 V GATE Turn Off Propagation Delay C GATE = 1nF 100 ns 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/ Current into RV Operating Temperature Range (Note 2) .. – 40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. ABSOLUTE AXI U RATI GSW WW U PACKAGE/ORDER I FOR ATIOUU W (Note 1) LT3750EMS ORDER PART NUMBER MS PART MARKING LTBQD TJMAX = 125°C, θJA = 120°C/ W V TRANS DONE CHARGE VCC GND RBG RV OUT RDCM GATE SOURCE TOP VIEW MS PACKAGE 10-LEAD PLASTIC MSOP The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VCC = VTRANS = 5V unless otherwise specified.
ELECTRICAL CHARACTERISTICS
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 LT3750E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Refer to Block Diagram for V DRAIN definition.
TYPICAL PERFOR A CE CHARACTERISTICS UW VCC Pin Current TEMPERATURE (°C) –50 –25 1.3 VCC PIN CURRENT (mA) 1.5 1.8 0 50 75
3750 G01
1.4 1.7 1.6 25 100 125 VCC = 24V VCC = 12V VCC = 3V TEMPERATURE (°C) –50 –25
100 VTRANS PIN CURRENT (µA)
3750 G02
VTRANS = 24V VTRANS = 12V VTRANS = 3V VCHARGE (V) CHARGE PIN CURRENT (µA)
3750 G03
40 –50°C 25°C 125°C VTRANS Pin Current CHARGE Pin Current CHARGE Pin Enable/Disable Voltage DONE Output Signal Low GATE High Voltage TEMPERATURE (°C) –50 0.6 0.7 0.9 25 75
3750 G04
0.5 0.4 –25 0 50 100 125 0.3 0.2 0.8 CHARGE PIN VOLTAGE (V) CHARGE PIN ENABLE CHARGE PIN DISABLE TEMPERATURE (°C) –50 DONE PIN VOLTAGE (mV)100 120 140 160 –25 0 25 50
3750 G05
VDONE = 5V RDONE = 100k TEMPERATURE (°C) –50 –25 GATE PIN VOLTAGE (V) 0 50 75
3750 G06
VCC = 24V VCC = 12V VCC = 5V DCM Comparator Trip Voltage VOUT Comparator Trip Voltage Current Limit Comparator Trip Voltage TEMPERATURE (°C) –50 –25 DCM COMPARATOR TRIP VOLTAGE (mV) 0 50 75
3750 G07
RDCM = 43k TEMPERATURE (°C) –50 –25 1.220VOUT COMPARATOR TRIP VOLTAGE (V) 1.228 1.240 0 50 75
3750 G08
1.224 1.236 1.232 25 100 125 TEMPERATURE (°C) –50 –25 CURRENT LIMIT COMPARATOR TRIP VOLTAGE (mV) 0 50 75
3750 G09
VTRANS (Pin 1): Transformer Supply Pin. Powers the primary coil of the transformer as well as internal circuitry that performs boundary mode detection. Bypass at the pin with a 1µF to 10µF capacitor. Bypass the primary winding of the transformer with a large capacitor. DONE (Pin 2): Open Collector Indication Pin. When target output voltage is reached, an NPN transistor turns on. Requires a pull-up resistor or current source. Any fault conditions such as thermal shutdown or undervoltage lockout will also turn on the NPN. CHARGE (Pin 3): Charge Pin. Initiates a new charge cycle when brought high or discontinues charging and puts part into shutdown when low. To properly enable the device, a step input with a minimum ramp rate of 1V/µs is required. Drive to 1.1V or higher to enable the device; drive below 0.2V to disable the device. V CC (Pin 4): Input Supply Pin. Bypass locally with a ceramic capacitor. A 1µF to 10µF ceramic capacitor should be sufficient for most applications. GND (Pin 5): Ground Pin. Connect directly to local ground plane. SOURCE (Pin 6): Source Pin. Senses NMOS drain current. Connect NMOS source terminal and current sense resistor to this pin. The current limit is 78mV/R SENSE. GATE (Pin 7): Gate Pin. Connect NMOS gate terminal to this pin. Internal gate driver will drive voltage to within V CC – 2V during each switching cycle. RDCM (Pin 8): Discontinuous Mode Sense Pin. Senses when current in transformer has decayed to zero and ini- tiates a new charge cycle if output voltage target has not been reached. Place a resistor between this pin and the drain of the NMOS. A good choice is a 43k, 5% resistor. RV OUT (Pin 9): Output Voltage VI Converter Pin. Develops a current proportional to output capacitor voltage. Con- nect a resistor between this pin and the drain of the NMOS. RBG (Pin 10): Output Voltage Sense Pin. Senses the voltage across the RBG resistor, which is proportional to the current flowing into the R VOUT pin. When voltage equals 1.24V, charging is disabled and DONE pin goes low. Connect a resistor (2.5k or less is recommended) from this pin to GND. A 2.49k, 1% resistor is a good choice.
160°C + – 2.8V DONE VTRANS VTRANS VDRAIN CHARGE RDONE RBG VCC 2.5V VTRANS VCC UVLO VTRANS UVLO VOUT COMPARATOR DCM COMPARATOR CURRENT LIMIT COMPARATOR 36mV VTRANS TSD Q ENABLE R Q S 1.24V ONE SHOT RBGGND ONE SHOT QR 78mV RSENSE 3750 BD S RDCM 7GATE VCC SOURCE RDCM RVOUT COUTVOUT D1T1 1:N RVOUT
- Start-up, 2. Primary-side charging, 3. Secondary en-
ergy transfer, 4. Discontinuous mode sensing. is reached or a fault condition resets it. on forcing VTRANS – VDS(ON) across the primary winding.
3750 F01a
3750 F01b
3750 F01c
Figure 1. Equivalent Circuits
3750 F02
Figure 2. Idealized Charging Waveforms
a rate (VTRANS – VDS(ON))/LPRI. The input voltage is mir- rored on the secondary winding –N • (VTRANS – VDS(ON)) which reverse biases the diode and prevents current flow in the secondary winding. Thus, energy is stored in the core of the transformer. 3. Secondary Energy Transfer When current limit is reached, the current limit compara- tor resets the NMOS on-latch and the device enters the third phase of operation, secondary energy transfer. The energy stored in the transformer core forward biases the diode and current flows into the output capacitor. During this time, the output voltage (neglecting the diode drop) is reflected back to the primary coil. If the target output voltage is reached, the V OUT comparator resets the master latch and the DONE pin goes low. Otherwise, the device enters the next phase of operation. 4. Discontinuous Mode Detection Once all the current is transferred to the output capacitor, OUT + VDIODE)/N will appear across the primary winding. A transformer with no energy cannot support a DC voltage, so, the voltage across the primary will decay to zero. In other words, the drain of the NMOS will ring down from V TRANS + (VOUT + V DIODE)/N to VTRANS. When the drain voltage falls to VTRANS + 36mV, the DCM comparator sets the NMOS on-latch and a new charge cycle begins. Steps 2-4 continue until the target output voltage is reached.
of the transformer, and the output. otherwise, the LT3750 may overcharge the output. particular transformer characteristics. ing the switching period to decrease with output voltage. Typical switching frequency is between 100kHz to 300kHz.
3750 F03
Figure 3. Typical Switching Period vs VOUT Table 1. Recommended Transformers
mentioned specifications to guarantee proper operation. and reverse bias leakage current should be considered. with adequate reverse recovery time. detect discontinuous mode after the first switching cycle. common in flyback regulators. Table 3. Recommended Output Capacitor Vendors Table 2. Recommended Output Diodes
Table 4 lists recommended NMOS transistors. current limit. The current limit is nominally 78mV/RSENSE. Use at least 1% tolerance resistors for R VOUT and R BG. 2.5k for typical applications. the diode forward voltage drop divided by N. Table 4. Recommended NMOS Transisitors
Figure 4. Recommended Board Layout
- Minimize the area of the high voltage end of the second-
- Provide sufficient spacing for all high voltage nodes
- Keep the electrical path formed by C1, the primary of T1
3750 F04
- +
300V, 3A Capacitor Charger VCC DONE CHARGE RVOUT RDCM GATE SOURCE VTRANS 60.4k 1:10 VOUT 300V VTRANS VCC 12V 100µF 43k 25mΩ
3750 TA02a
4, 5 6, 7 2.49k 33pF OFF ON 10µF 10µF 56µF C1: 25V X5R OR X7R CERAMIC CAPACITOR C2: 25V X5R OR X7R CERAMIC CAPACITOR C3: 25V SANYO OS-CON 25SVP56M C4: 330V RUBYCON PHOTOFLASH CAPACITOR D1: DIODES INC. MURS160 M1: PHILIPS PHT6NQ10T T1: TDK DCT15EFD-U44S003 FLYBACK TRANSFORMER VOUT (V) EFFICIENCY (%) 100 50 100 150 200
3750 TA02b
VTRANS = 18V VTRANS = 6VVTRANS = 12V TIME (SECONDS) VOUT (V) 100 150 200 250 300 0.2 0.4 0.6 0.8
3750 TA02c
1.0 VTRANS = 18V VTRANS = 6V VTRANS = 12V 3A Charging Efficiency 3A Charge Time NMOS DRAIN CURRENT 1A/DIV NMOS DRAIN VOLTAGE 20V/DIV 5µs/DIV
3750 TA02d
Typical Switching Waveforms
300V, 6A Capacitor Charger 6A Charging Efficiency 6A Charge Time VCC DONE CHARGE RVOUT RDCM GATE SOURCE VTRANS 60.4k 1:10 VOUT 300V VTRANS VCC 12V 100µF 43k 12mΩ
3750 TA03a
2.49k 100pF OFF ON 10µF 10µF 56µF C1: 25V X5R OR X7R CERAMIC CAPACITOR C2: 25V X5R OR X7R CERAMIC CAPACITOR C3: 25V SANYO OS-CON 25SVP56M C4: 330V RUBYCON PHOTOFLASH CAPACITOR D1: DIODES INC. MURS160 M1: PHILIPS PHT6NQ10T T1: TDK DCT20EFD-U32S003 FLYBACK TRANSFORMER 3, 4, 5, 6 7, 8, 9, 10 VOUT (V) EFFICIENCY (%) 100 50 100 150 200
3750 TA03b
VTRANS = 18V VTRANS = 6V VTRANS = 12V TIME (SECONDS) VOUT (V) 100 150 200 250 300 0.1 0.2 0.3 0.4 0.5 VTRANS = 18V VTRANS = 6V VTRANS = 12V NMOS DRAIN CURRENT 2A/DIV NMOS DRAIN VOLTAGE 20V/DIV 5µs/DIV
3750 TA03d
Typical Switching Waveforms
300V, 9A Capacitor Charger 9A Charging Efficiency 9A Charge Time VCC DONE CHARGE RVOUT RDCM GATE SOURCE VTRANS 60.4k 1:10 VOUT 300V VTRANS VCC 12V 100µF 43k 8mΩ
3750 TA04a
2.49k 100pF OFF ON 10µF C1: 25V X5R OR X7R CERAMIC CAPACITOR C2: 25V X5R OR X7R CERAMIC CAPACITOR C3: 25V SANYO OS-CON 25SVP56M C4: 330V RUBYCON PHOTOFLASH CAPACITOR D1: DIODES INC. MURS160 M1: PHILIPS PHM2INQ15T T1: TDK DCT20EFD-U32S003 FLYBACK TRANSFORMER 10µF 56µF 3, 4, 5, 6 7, 8, 9, 10 VOUT (V) EFFICIENCY (%) 100 50 100 150 200
3750 TA04b
VTRANS = 18V VTRANS = 6V VTRANS = 12V TIME (SECONDS) VOUT (V) 100 150 200 250 300 0.05 0.10 0.15 0.20
3750 TA04c
0.300.25 VTRANS = 18V VTRANS = 6V VTRANS = 12V NMOS DRAIN CURRENT 4A/DIV NMOS DRAIN VOLTAGE 20V/DIV 5µs/DIV
3750 TA04d
Typical Switching Waveforms
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. UPACKAGE DESCRIPTIO 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) MSOP (MS) 0603 0.53 ± 0.152 (.021 ± .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 0.127 ± 0.076 (.005 ± .003) 0.86 (.034) REF 0.50 (.0197) BSC 12 3 45 4.90 ± 0.152 (.193 ± .006) 0.497 ± 0.076 (.0196 ± .003) REF8910 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.889 ± 0.127 (.035 ± .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 ± 0.038 (.0120 ± .0015) TYP 0.50 (.0197) BSC
© LINEAR TECHNOLOGY CORPORATION 2005 LT 0106 REV A • PRINTED IN THE USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com TYPICAL APPLICATIO U 300V, 9A, 2.5mF Capacitor Charger VCC DONE CHARGE RVOUT RDCM GATE SOURCE VTRANS 60.4k 1:10 VOUT 300V VTRANS VCC 12V 2.5mF 43k 8mΩ
3750 TA05a
2.49k 100pF OFF ON 10µF C1, C2: 25V X5R OR X7R CERAMIC CAPACITOR C3: 25V SANYO OS-CON 25SVP56M C4: CORNELL DUBILIER 7P252V360N082 D1: DIODES INC. MURS160 M1: PHILIPS PHM21NQ15T T1: MIDCOM 32052 FLYBACK TRANSFORMER 10µF 56µF 4, 5 6, 7 Efficiency Charge Time VOUT (V) EFFICIENCY (%)80 100 50 100 150 200
3750 TA05b
VTRANS = 18V VTRANS = 6V VTRANS = 12V TIME (SECONDS) VOUT (V) 100 150 200 250 300 123456
3750 TA05c
VTRANS = 18V VTRANS = 6V VTRANS = 12V PART NUMBER DESCRIPTION COMMENTS LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Charger with Charges 220 µF to 320V in 3.7 Seconds from 5V, VIN: 2.2V to 16V, Automatic Top-Off I SD < 1µA, 10-Lead MS Package LT3468/LT3468-1 1.4A, 1A, 0.7A, Photoflash Capacitor Charger V IN: 2.5V to 16V, Charge Time: 4.6 Seconds for LT3468 (0V to 320V, 100µF, LT3468-2 V IN = 3.6V), ISD < 1µA, ThinSOT Package LT3484-0/LT3484-1 1.4A, 0.7A, 1A Photoflash Capacitor Charger V IN: 1.8V to 16V, Charge Time: 4.6 Seconds for LT3484-0 LT3484-2 (0V to 320V, 100 µF, VIN = 3.6V), ISD < 1µA, 2mm × 3mm 6-Lead LT3485-0/LT3485-1 1.4A, 0.7A, 1A, 2A Photoflash Capacitor Charger V IN: 1.8V to 10V, Charge Time: 3.7 Seconds for LT3485-0 LT3485-2/LT3485-3 with Output Voltage Monitor and Integrated IGBT (0V to 320V, 100 µF, VIN = 3.6V), ISD < 1µA, 3mm × 3mm 10-Lead DFN Driver RELATED PARTS