LT3751 High Voltage Capacitor Charger Controller with Regulation Description Features n n n n n n n n n n Charges Any Size Capacitor Low Noise Output in Voltage Regulation Mode Stable Operation Under a No-Load Condition Integrated 2A MOSFET Gate Driver with Rail-to-Rail Operation for VCC ≤ 8V Selectable 5.6V or 10.
LT3751 Absolute Maximum Ratings (Note 1) VCC, CHARGE, CLAMP...............................................24V DONE, FAULT.............................................................24V LVGATE (Note 8)........................................................24V VCC – LVGATE..............................................................8V HVGATE.................................................................Note 9 RBG, CSP, CSN............................................................2V FB ...............
LT3751 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VCC = CHARGE = 5V, CLAMP = 0V, unless otherwise noted. Individual 25kΩ resistors tied from 5V VTRANS supply to RVTRANS, RVOUT, RDCM, unless otherwise noted. (Note 2) PARAMETER CONDITIONS VCC Voltage MIN MAX UNITS l 4.75 24 V l 4.75 65 V 5.
LT3751 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VCC = CHARGE = 5V, CLAMP = 0V, unless otherwise noted. Individual 25kΩ resistors tied from 5V VTRANS supply to RVTRANS, RVOUT, RDCM, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS UVLO1 Threshold Measured from Pin to GND UVLO2 Threshold Measured from Pin to GND l 1.195 1.225 1.255 V l 1.195 1.225 1.
LT3751 Typical Performance Characteristics VCC Pin Current 150 IVTRANS CURRENT (µA) PIN CURRENT (mA) CHARGE Pin Current 5 4 3 2 –40°C 25°C 125°C 1 0 4 12 8 16 PIN VOLTAGE (V) 130 125 120 110 10 30 20 40 PIN VOLTAGE (V) 50 1.1 1.1 1.0 0.9 0.8 VCC = 5V VCC = 12V VCC = 24V 20 40 60 80 TEMPERATURE (°C) 0.9 0.8 0.
LT3751 Typical Performance Characteristics Current Comparator Trip Voltage (Charge Mode) VTH = VCSP – VCSN VTH = VCSP – VCSN 12.8 FB = 1.3V 12.6 VTH VOLTAGE (mV) VTH VOLTAGE (mV) 108.5 108.0 107.5 107.0 –40 –20 20 40 60 80 TEMPERATURE (°C) 12.2 12.0 11.8 11.6 VCC = 5V VCC = 12V VCC = 24V 11.2 11.0 –40 –20 100 120 0 20 40 60 80 TEMPERATURE (°C) SOURCED PIN CURRENT (nA) 1.219 –40 –20 60 1.168 60 1.160 1.156 40 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 1.
LT3751 typical performance characteristics 10.8 10.7 10.6 0.64 VCC = 12V CLAMP = 12V 0.62 5.65 DCM TRIP VOLTAGE (V) HVGATE PIN VOLTAGE (V) 10.9 5.70 VCC = 24V CLAMP = 0V HVGATE PIN VOLTAGE (V) 11.0 DCM Trip Voltage (VDRAIN – VTRANS), RVTRANS = RDCM = 25kΩ HVGATE Pin Clamp Voltage HVGATE Pin Clamp Voltage 5.60 5.55 0 20 40 60 80 TEMPERATURE (°C) 100 120 5.50 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 3751 G19 Pin Functions 0.60 0.58 0.56 10.5 10.
LT3751 Pin Functions DONE (Pin 7/ Pin 5): Open Collector Indication Pin. When the target output voltage (charge mode) is reached or the FAULT pin goes low, a transistor turns on. This pin needs a proper pull-up resistor or current source. CHARGE (Pin 8/Pin 6): Charge Pin. Initiates a new charge cycle (charge mode) or enables the part (regulation mode) when driven higher than 1.5V. Bring this pin below 0.3V to discontinue charging and put the part into shutdown.
LT3751 Block Diagram DONE ENABLE GATE DRIVER – 100k DCM COMPARATOR DCM ONE-SHOT S R FAULT Q Q LATCH VTRANS RUVLO1 191k DIFF. AMP COMPARATOR WITH INTERNAL 60V CLAMPS 3.8V + VCC – UVLO1 LVGATE 162mV – +– + 26kHz ONE-SHOT CLOCK MAIN 106mV – +– – TO CHARGE ONE-SHOT + 26kHz ONE-SHOT CLOCK ERROR AMP + – TO VOUT COMPARATOR GND RBG 1.33k DIE TEMP RSENSE 12mΩ 160ºC + 1.22V REFERENCE A1 – + – 55V CSN TIMING AND PEAK CURRENT CONTROL 11mV TO 106mV MODULATION 55V 1.
LT3751 Operation The LT3751 can be used as either a fast, efficient high voltage capacitor charger controller or as a high voltage, low noise voltage regulator. The FB pin voltage determines one of the three primary modes: charge mode, low noise regulation, or no-load operation (see Figure 1). FB PIN VOLTAGE ILPRI IPK VTRANS – VDS(ON) LPRI ILSEC NO-LOAD OPERATION VOUT + VDIODE LSEC IPK N 1.34V REGULATION 1.16V CHARGE MODE VPRI VTRANS – VDS(ON) 0.0V 3751 F01 Figure 1.
LT3751 operation Information section for proper use of LVGATE). With the gate driver output high, the external NMOS turns on, forcing VTRANS – VDS(ON) across the primary winding. Consequently, current in the primary coil rises linearly at a rate (VTRANS – VDS(ON))/LPRI. The input voltage is mirrored 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.
LT3751 Operation At very low output voltages, the boundary-mode switching cycle period increases significantly such that the energy stored in the transformer core is not depleted before the next clock cycle. In this situation, the clock may initiate another switching cycle before the secondary winding current reaches zero and cause the LT3751 to enter continuous-mode conduction.
LT3751 operation CHARGE MODE LIGHT LOAD OPERATION 26kHz ONE-SHOT CLK SWITCH ENABLE 26kHz ONE-SHOT CLK ... ... ... MAXIMUM PEAK CURRENT NO BLANKING SWITCH ENABLE IPRI IPRI ... DUTY CYCLE CONTROL ... t tPER ≈ 38µs NO-LOAD OPERATION HEAVY LOAD OPERATION 26kHz ONE-SHOT CLK 26kHz ONE-SHOT CLK ... FORCED BLANKING ... FORCED BLANKING t SWITCH ENABLE DUTY CYCLE CONTROL 110% VOUT, NOM VOUT ... PEAK CURRENT CONTROL ... ... 105% VOUT, NOM ... IPRI 1/10TH IPK IPRI ...
LT3751 Operation Periodic Refresh Light Load Operation When the LT3751 enters regulation, the internal circuitry deactivates switching when the internal one-shot clock is high. The clock operates at a 1/20th duty cycle with a minimum blank time of 1.5µs. This reset pulse is timed to drastically reduce switching frequency content within the audio spectrum and is active during all loading conditions. Each reset pulse guarantees at least one energy cycle.
LT3751 Applications Information The LT3751 charger controller can be optimized for either capacitor charging only or low noise regulation applications. Several equations are provided to aid in the design process. Large capacitors charged to high voltage can deliver a lethal amount of energy if handled improperly. It is particularly important to observe appropriate safety measures when designing the LT3751 into applications.
LT3751 Applications Information The total propagation delay, td, is the second most dominant factor that affects efficiency and is the summation of gate driver on-off propagation delays and the discharge time associated with the secondary winding capacitance. There are two effective methods to reduce the total propagation delay. First, reduce the total capacitance on the secondary winding, most notably the diode capacitance. Second, reduce the total required NMOS gate charge.
LT3751 applications information Table 1. Recommended Transformers MANUFACTURER PART NUMBER SIZE L × W × H (mm) MAXIMUM IPRI (A) LPRI (µH) TURNS RATIO (PRI:SEC) Coilcraft www.coilcraft.com DA2033-AL DA2034-AL GA3459-BL GA3460-BL HA4060-AL HA3994-AL 17.4 × 24.1 × 10.2 20.6 × 30 × 11.3 32.65 × 26.75 × 14 32.65 × 26.75 × 14 34.29 × 26.75 × 14 34.29 × 28.75 × 14 5 10 20 50 2 5 10 10 5 2.5 300 7.5 1:10 1:10 1:10 1:10 1:3 2:1:3:3* Würth Elektronik/Midcom www.we-online.
LT3751 Applications Information with VTRANS between 100V and 400V (refer to Typical Applications section). Consult applications engineering for applications with VTRANS operating above 400V. RVOUT is required for capacitor charger applications but may be removed for regulator applications. Note that the VOUT comparator can be used as secondary protection for regulator applications. If the VOUT comparator is used for protection, design VOUT,TRIP 15% to 20% higher than the regulation voltage.
LT3751 applications information Table 4. Recommended Output Diodes MANUFACTURER PART NUMBER IF(AV) (A) VRRM (V) TRR (ns) PACKAGE Central Semiconductor www.centralsemi.com CMR1U-10M CMSH2-60M CMSH5-40 1 2 5 1000 60 40 100 SMA SMA SMC Fairchild Semiconductor www.fairchildsemi.com ES3J ES1G ES1J 3 1 1 600 400 600 35 35 35 SMC SMA SMA On Semiconductor www.onsemi.com MURS360 MURA260 MURA160 3 2 1 600 600 600 75 75 75 SMC SMA SMA Vishay www.vishay.
LT3751 Applications Information detected to when the gate transitions to the low state. This delay increases the peak current limit by (VTRANS) (180ns)/LPRI. of resistor values. When under/overvoltage lockout comparators are tripped, the master latch is disabled, power delivery is halted, and the FAULT pin goes low. Sense resistor inductance (LRSENSE) is another source of current limit error.
LT3751 applications information unnecessarily high V(BR)DSS which equates to a larger RDS(ON). Secondly, the VDRAIN node will ring—possibly below ground—causing false tripping of the DCM comparator or damage to the NMOS switch (see Figure 11). Both issues can be remedied using a snubber. If leakage inductance causes issues, it is recommended to use a RC snubber in parallel with the primary winding, as shown in Figure 10.
LT3751 Applications Information Large Signal Stability Small Signal Stability Large signal stability can be an issue when audible noise is a concern. Figure 12 shows that the problem originates from the one-shot clock and the output voltage ripple. The load must be constrained such that the output voltage ripple does not exceed the regulation range of the error amplifier within one clock period (approximately 6mV referred to the FB pin).
ANALOG GND CHARGE VCC RDONE RFAULT ROVLO2 RUVLO2 + VTRANS ROVLO1 RUVLO1 18 16 6 5 4 9 RFBH3 RFBL CFB 11 12 SINGLE POINT GND ANALOG GND VCC RBG RVOUT RDCM CVTRANS4 POWER GND RETURN CVCC CVTRANS3 M1 RSENSE ANALOG GND RFBH2 REMOVE COPPER FROM ALL SUB-LAYERS (SEE ITEM 4) T1 1:N • RFBH1 • POWER GND RETURN SECONDARY Figure 14.
CHARGE VCC RDONE RFAULT ROVLO2 RUVLO2 ROVLO1 RUVLO1 RVTRANS 17 16 4 5 13 12 11 8 9 10 POWER GND RETURN ANALOG GND VCC RSENSE CVCC RBG RVOUT RDCM REMOVE COPPER FROM ALL SUB-LAYERS (SEE ITEM 4) CVTRANS2 + CVTRANS4 M1 ANALOG GND POWER GND RETURN CVTRANS3 • T1 1:N Figure 15.
LT3751 Typical Applications 42A Capacitor Charger DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VTRANS 12V TO 24V T1** 1:10 + OFF ON VCC 12V TO 24V C1 10µF R1, 191k R2, 475k R3, 191k VCC R7, 18.2k VCC R8, 40.2k LT3751 R4, 475k DONE RVOUT HVGATE LVGATE CSP FAULT UVLO1 OVLO1 CSN UVLO2 FB VCC D2*** • RVTRANS CHARGE CLAMP RDCM R10, 100k R11, 100k VTRANS C2 10µF ×3 R6 40.
LT3751 typical applications High Voltage Regulator DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VTRANS 5V TO 24V + T1* 1:10 C3 680µF C1 10µF DONE TO MICRO R1, 69.8k VTRANS R2, 475k R3, 69.8k VCC R6 40.2k RVTRANS CHARGE RDCM CLAMP LT3751 VCC RVOUT OFF ON VCC 5V TO 24V C2 5× 2.2µF R4, 475k UVLO1 • R7, 18.
LT3751 typical applications 1.6A High Input Voltage, Isolated Capacitor Charger DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VTRANS 100V TO 400VDC T1* 1:3 F1, 1A + R6 625k C3 47µF R7, 96.2k OFF ON VCC 10V TO 24V C1 10µF TO MICRO R1, 1.5M VTRANS R2, 9M R3, 154k VCC R4, 475k R9 67.3k HVGATE LVGATE FB OVLO1 • VCC 4.
LT3751 typical applications High Input Voltage, High Output Voltage Regulator DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY VTRANS 100V TO 400VDC T1* 1:3 F1, 1A + C3 47µF C1 10µF DONE TO MICRO R1, 1.5M VTRANS R2, 9M R3, 154k VCC R7, 97.6k RVTRANS CHARGE RDCM CLAMP LT3751 VCC RVOUT OFF ON VCC 10V TO 24V R6, 625k R4, 475k FAULT UVLO1 OVLO1 UVLO2 OVLO2 HVGATE LVGATE CSP C2 2.
LT3751 typical applications Isolated 282V Voltage Regulator DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY D2 R2, 10Ω ISOLATION BOUNDARY • T1 Npb VTRANS 100V TO 200VDC F1, 2A VTRANS R1 49.9k D5 + M1 C3 22µF ×2 OFF ON C1 100pF RVTRANS RDCM CHARGE CLAMP LT3751 RV V CC Load Regulation R4 105k R5 210k • Np D3 R16 249k • C5 0.01µF VCC Nsb R15 5.
LT3751 typical applications Wide Input Voltage Range, 15 Watt, Triple Output Voltage Regulator T1 2:1:3:3 (P1:S1:S2:S3) D1 VIN 5V TO 24V + C2 1000µF ×2 R5 25.5k RVTRANS CHARGE CLAMP OFF ON C1 10µF R1, 100k R2, 100k R3, 66.5k C1, C3: 25V X5R OR X7R CERAMIC C2: 25V SANYO 25ME1000AX C4, C5: 35V SANYO 35ME470AX C6: 10V KEMET T520D107M010ASE055 C7, C8: 16V CERAMIC, TDK C4532X7R1E106M C9: 6.
LT3751 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 20-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663 Rev I) Exposed Pad Variation CB 6.40 – 6.60* (.252 – .260) 3.86 (.152) 3.86 (.152) 20 1918 17 16 15 14 13 12 11 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 6.40 2.74 (.252) (.108) BSC SEE NOTE 4 0.45 ±0.05 1.05 ±0.10 0.65 BSC 1 2 3 4 5 6 7 8 9 10 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.
LT3751 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UFD Package 20-Pin Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1711 Rev B) 0.70 ±0.05 4.50 ± 0.05 1.50 REF 3.10 ± 0.05 2.65 ± 0.05 3.65 ± 0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.50 REF 4.10 ± 0.05 5.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 (2 SIDES) 0.75 ± 0.05 PIN 1 NOTCH R = 0.20 OR C = 0.
LT3751 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION B 5/10 Updated FAULT (Pin 6/Pin 4) description in Pin Functions 7 Updated DONE (Pin 7/Pin 5) description in Pin Functions 8 Updated Block Diagram 9 C 6/12 PAGE NUMBER Revised Applications Information section 17, 18 Revised Typical Applications illustration 30 Revised Applications Information section 20 Corrected Schematic R8 value from 3.40k to 2.
LT3751 Typical Application 300V Regulated Power Supply VTRANS 24V T1 1:10 + C3 680µF OFF ON R6 40.2k RVTRANS CHARGE CLAMP VCC 24V C1 10µF C2 2.2µF ×5 RDCM R7 18.2k • D1 + • RVOUT VCC TO MICRO R1 432k VTRANS R2 475k R3 432k VCC R4 475k C4 20µF VOUT 300V 0mA TO 270mA HVGATE LVGATE CSP DONE FAULT R5 6mΩ UVLO1 LT3751 OVLO1 CSN UVLO2 FB R9 1.
