LTC3803-5 Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT FEATURES DESCRIPTION n VIN and VOUT Limited Only by External Components The LTC®3803-5 is a constant frequency current mode n 4.8V Undervoltage Lockout Threshold fl yback controller optimized for driving N-channel MOSFETs n Operating Junction Temperature from –55°C to in high input voltage applications. The LTC3803-5 operates 150°C from inputs as low as 5V. Constant frequency operation n Adjustable Slope Compensation is maintained down to very light loads, resulting in less n Internal Soft-Start low frequency noise generation over a wide range of load n Constant Frequency 200kHz Operation currents. Slope compensation can be programmed with n ±1.5% Reference Accuracy an external resistor. n Current Mode Operation for Excellent Line and Load The LTC3803-5 provides ±1.5% output voltage accuracy Transient Response and consumes only 240μA of quiescent current. Ground- n No Minimum Load Requirement referenced current sensing allows LTC3803-5-based con- n Low Quiescent Current: 240μA verters to accept input supplies beyond the LTC3803-5’s n Low Profi le (1mm) SOT-23 Package absolute maximum V . For simplicity, the LTC3803-5 can CC be powered from a high V through a resistor, due to its IN APPLICATIONS internal shunt regulator. An internal undervoltage lockout n 42V and 12V Automotive Power Supplies shuts down the IC when the input voltage is too low to n Telecom Power Supplies provide suffi cient gate drive to the external MOSFET. n Auxiliary/Housekeeping Power Supplies The LTC3803-5 is available in a low profi le (1mm) 6-lead n Power Over Ethernet SOT-23 (ThinSOT™) package. L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks and ThinSOT and No RSENSE are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Effi ciency and Power Loss Dual Output Wide Input Range Converter vs Output Power 10MQ100N VIN VPH5-0155 13V/0.3A 90 3.0 6V TO 50V 1μF 20mA MIN VIN = 8V 100V LOAD 22k PDZ6.8B ×3 22μF 85 VIN = 12V 2.5 10V MMBTA42 10nF 7.5k IGTNHD/LRTUCN380N3G-5AVTCEC PH4M.72k5NQ10T 11001100μμVVFF 6.5V/1.2A EFFICIENCY (%) 877050 VIN = 24V 211...050POWER LOSS (W) VFB SENSE B3100 47μF VIN = 48V 8.06k 0.012Ω 10V 65 0.5 0.1μF 57.6k 60 VIN = 12V 0 0 2 4 6 8 10 12 ALL CAPACITORS ARE X7R, TDK OUTPUT POWER (W) 38035 TA01 38035 TA01b 38035fd 1

LTC3803-5 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) V to GND (Current Fed) ..................... 25mA into V * CC CC NGATE Voltage .......................................... –0.3V to V CC V , I /RUN Voltages...............................–0.3V to 3.5V TOP VIEW FB TH SENSE Voltage ............................................ –0.3V to 1V ITH/RUN 1 6 NGATE NGATE Peak Output Current (<10μs) ......................... 1A GND 2 5 VCC Operating Junction Temperature Range (Notes 2, 3) VFB 3 4 SENSE LTC3803E-5 .......................................–40°C to 125°C S6 PACKAGE LTC3803I-5 ........................................–40°C to 125°C 6-LEAD PLASTIC TSOT-23 TJMAX = 150°C, θJA = 192°C/W LTC3803H-5 (Note 3) .........................–40°C to 150°C LTC3803MP-5 (Note 3) ......................–55°C to 150°C Storage Temperature Range ...................–65°C to 150°C Lead Temperature (Soldering, 10 sec) ..................300°C *LTC3803-5 internal clamp circuit self regulates V voltage to 8.1V. CC ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3803ES6-5#PBF LTC3803ES6-5#TRPBF LTBPF 6-Lead Low Profi le (1mm) SOT-23 –40°C to 125°C LTC3803IS6-5#PBF LTC3803IS6-5#TRPBF LTBMH 6-Lead Low Profi le (1mm) SOT-23 –40°C to 125°C LTC3803HS6-5#PBF LTC3803HS6-5#TRPBF LTBMH 6-Lead Low Profi le (1mm) SOT-23 –40°C to 150°C LTC3803MPS6-5#PBF LTC3803MPS6-5#TRPBF LTBMH 6-Lead Low Profi le (1mm) SOT-23 –55°C to 150°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3803ES6-5 LTC3803ES6-5#TR LTBPF 6-Lead Low Profi le (1mm) SOT-23 –40°C to 125°C LTC3803IS6-5 LTC3803IS6-5#TR LTBMH 6-Lead Low Profi le (1mm) SOT-23 –40°C to 125°C LTC3803HS6-5 LTC3803HS6-5#TR LTBMH 6-Lead Low Profi le (1mm) SOT-23 –40°C to 150°C LTC3803MPS6-5 LTC3803MPS6-5#TR LTBMH 6-Lead Low Profi le (1mm) SOT-23 –55°C to 150°C Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi ed by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating junction temperature range, otherwise specifi cations are at T = 25°C. V = 5V, unless otherwise noted. (Notes 2, 3) A CC SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V V Turn On Voltage LTC3803E-5 l 4 4.8 5.7 V TURNON CC LTC3803I-5, LTC3803H-5, LTC3803MP-5 l 3.9 4.8 5.7 V V V Turn Off Voltage LTC3803E-5 l 3.3 4 4.9 V TURNOFF CC LTC3803I-5, LTC3803H-5, LTC3803MP-5 l 3.2 4 4.9 V V V Hysteresis V – V l 0.05 0.8 V HYST CC TURNON TURNOFF V V Shunt Regulator Voltage at 1mA I = 1mA, V = 0V CLAMP1mA CC CC ITH/RUN LTC3803E-5 l 6.2 8 9.9 V LTC3803I-5, LTC3803H-5 l 6.2 8 10.4 V LTC3803MP-5 l 5.9 8 10.4 V 38035fd 2

LTC3803-5 ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating junction temperature range, otherwise specifi cations are at T = 25°C. V = 5V, unless otherwise noted. (Notes 2, 3) A CC SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V V Shunt Regulator Voltage at 25mA I = 25mA, V = 0V CLAMP25mA CC CC ITH/RUN LTC3803E-5 l 6.3 8.1 10.3 V LTC3803I-5, LTC3803H-5 l 6.3 8.1 10.7 V LTC3803MP-5 l 6 8.1 10.7 V I Input DC Supply Current in (Note 4) CC Normal Operation V = 1.3V 240 350 μA ITH/RUN I Input DC Supply Current in V = V – 100mV CC,(UV) CC TURNON Undervoltage LTC3803E-5 l 40 90 μA LTC3803I-5, LTC3803H-5, LTC3803MP-5 l 40 100 μA V Shutdown Threshold (at I /RUN) V > V , V Falling ITHSHDN TH CC TURNON ITH/RUN LTC3803E-5 l 0.12 0.28 0.45 V LTC3803I-5, LTC3803H-5 l 0.08 0.28 0.45 V LTC3803MP-5 l 0.08 0.28 0.47 V I Start-Up Current Source V = 0V ITHSTART ITH/RUN LTC3803E-5 l 0.07 0.34 0.8 μA LTC3803I-5, LTC3803H-5, LTC3803MP-5 l 0.07 0.34 1 μA V Regulated Feedback Voltage (Note 5) FB LTC3803E-5: 0°C ≤ T ≤ 85°C 0.788 0.800 0.812 V J –40°C ≤ T ≤ 85°C l 0.780 0.800 0.816 V J LTC3803I-5: 0°C ≤ T ≤ 85°C 0.788 0.800 0.812 V J –40°C ≤ T ≤ 125°C l 0.780 0.800 0.820 V J LTC3803H-5: 0°C ≤ T ≤ 85°C 0.788 0.800 0.812 V J –40°C ≤ T ≤ 150°C l 0.780 0.800 0.820 V J LTC3803MP-5: 0°C ≤ T ≤ 85°C 0.788 0.800 0.812 V J –55°C ≤ T ≤ 150°C l 0.780 0.800 0.820 V J g Error Amplifi er Transconductance I Pin Load = ±5μA (Note 5) 200 333 500 μA/V m TH/RUN ΔV Output Voltage Line Regulation (Note 5) 0.1 mV/V O(LINE) ΔV Output Voltage Load Regulation I Sinking 5μA (Note 5) 3 mV/μA O(LOAD) TH/RUN I Sourcing 5μA (Note 5) 3 mV/μA TH/RUN I V Input Current (Note 5) 10 50 nA FB FB f Oscillator Frequency V = 1.3V 170 200 230 kHz OSC ITH/RUN DC Minimum Switch On Duty Cycle V = 1.3V, V = 0.8V 6.5 8.5 % ON(MIN) ITH/RUN FB DC Maximum Switch On Duty Cycle V = 1.3V, V = 0.8V 70 80 90 % ON(MAX) ITH/RUN FB t Gate Drive Rise Time C = 3000pF 40 ns RISE LOAD t Gate Drive Fall Time C = 3000pF (Note 7) 40 ns FALL LOAD V Peak Current Sense Voltage R = 0 (Note 6) IMAX SL LTC3803E-5 l 90 100 115 mV LTC3803I-5, LTC3803H-5 l 85 100 115 mV LTC3803MP-5 l 85 100 120 mV I Peak Slope Compensation Output (Note 7) 5 μA SLMAX Current t Soft-Start Time 0.7 ms SFST 38035fd 3

LTC3803-5 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings Junction temperature (T ) is calculated from the ambient temperature T J A may cause permanent damage to the device. Exposure to any Absolute and the power dissipation P in the LTC3803-5 using the formula: D Maximum Rating condition for extended periods may affect device T = T + (P • 230°C/W) J A D reliability and lifetime. Note 3: High junction temperatures degrade operating lifetimes; operating Note 2: The LTC3803-5 is tested under pulsed load conditions such lifetime is derated for junction temperatures greater than 125°C. that T ≈ T . The LTC3803E-5 is guaranteed to meet specifi cations J A Note 4: Dynamic supply current is higher due to the gate charge being from 0°C to 85°C junction temperature. Specifi cations over the –40°C delivered at the switching frequency. to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The Note 5: The LTC3803-5 is tested in a feedback loop that servos VFB to the LTC3803I-5 is guaranteed over the –40°C to 125°C operating junction output of the error amplifi er while maintaining ITH/RUN at the midpoint of temperature range, the LTC3803H-5 is guaranteed over the –40°C to the current limit range. 150°C operating junction temperature range and the LTC3803MP-5 is Note 6: Peak current sense voltage is reduced dependent on duty cycle tested and guaranteed over the full –55°C to 150°C operating junction and an optional external resistor in series with the SENSE pin (R ). For SL temperature range. Note that the maximum ambient temperature details, refer to the programmable slope compensation feature in the consistent with these specifi cations is determined by specifi c operating Applications Information section. conditions in conjunction with board layout, the rated package thermal Note 7: Guaranteed by design. impedance and other environmental factors. TYPICAL PERFORMANCE CHARACTERISTICS Reference Voltage Reference Voltage Reference Voltage vs Temperature vs Supply Voltage vs V Shunt Regulator Current CC 820 812 812 VCC = 5V TA = 25°C TA = 25°C 815 VCC ≤ VCLAMP1mA 808 808 810 E (mV) 805 E (mV) 804 E (mV) 804 G G G TA 800 TA 800 TA 800 L L L O O O V VFB 795 V VFB 796 V VFB796 790 792 792 785 780 788 788 –60 –30 0 30 60 90 120 150 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 0 5 10 15 20 25 TEMPERATURE (°C) VCC SUPPLY VOLTAGE (V) ICC (mA) 38035 G01 38035 G02 38035 G03 Oscillator Frequency Oscillator Frequency Oscillator Frequency vs Temperature vs Supply Voltage vs V Shunt Regulator Current CC 240 220 220 VCC = 5V TA = 25°C TA = 25°C 215 215 Hz) 230 Hz) Hz) Y (k Y (k210 Y (k210 C 220 C C EN EN205 EN205 U U U Q Q Q RE 210 RE200 RE200 F F F R R R ATO 200 ATO195 ATO195 L L L CIL CIL190 CIL190 S S S O 190 O O 185 185 180 180 180 –60 –30 0 30 60 90 120 150 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 0 5 10 15 20 25 TEMPERATURE (°C) VCC SUPPLY VOLTAGE (V) ICC (mA) 38035 G04 38035 G05 38035 G06 38035fd 4

LTC3803-5 TYPICAL PERFORMANCE CHARACTERISTICS V Undervoltage Lockout V Shunt Regulator Voltage I Supply Current CC CC CC Thresholds vs Temperature vs Temperature vs Temperature 6.0 10.5 300 VCC = 5V VITH/RUN = 1.3V 5.5 10.0 280 5.0 VTURNON 9.5 T (μA) N 260 VOLTS 4.5 V (V)CC 89..50 ICC = 25mA Y CURRE 240 L 4.0 PP VTURNOFF 8.0 ICC = 1mA SU 220 3.5 7.5 3.0 7.0 200 –60 –30 0 30 60 90 120 150 –60 –30 0 30 60 90 120 150 –60 –30 0 30 60 90 120 150 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 38035 G07 38035 G08 38035 G09 Start-Up I Supply Current I /RUN Shutdown Threshold I /RUN Start-Up Current Source CC TH TH vs Temperature vs Temperature vs Temperature 70 500 1000 VCC = VTURNON – 0.1V VCC = VTURNON + 0.1V START-UP SUPPLY CURRENT (μA) 341652000000 SHUTDOWN THRESHOLD (mV) 13442213050055055000000000 I/RUN PIN CURRENT SOURCE (nA)TH314678952000000000000000000 VITH/RUN = 0V 0 0 0 –60 –30 0 30 60 90 120 150 –60 –30 0 30 60 90 120 150 –60 –30 0 30 60 90 120 150 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 38035 G10 38035 G11 38035 G12 Peak Current Sense Voltage vs Temperature Soft-Start Time vs Temperature 120 1.4 VCC = 5V VCC = 5V 115 1.2 AGE (mV) 111005 ME (ms) 1.0 VOLT 100 RT TI 0.8 E PIN 95 T-STA 0.6 S F N O 0.4 SE 90 S 85 0.2 80 0 –60 –30 0 30 60 90 120 150 –60 –30 0 30 60 90 120 150 TEMPERATURE (°C) TEMPERATURE (°C) 38035 G13 38035 G14 38035fd 5

LTC3803-5 PIN FUNCTIONS I /RUN (Pin 1): This pin performs two functions. It SENSE (Pin 4): This pin performs two functions. It monitors TH serves as the error amplifi er compensation point as well switch current by reading the voltage across an external as the run/shutdown control input. Nominal voltage range current sense resistor to ground. It also injects a current is 0.7V to 1.9V. Forcing this pin below the shutdown ramp that develops slope compensation voltage across threshold (V ) causes the LTC3803-5 to shut down. an optional external programming resistor. ITHSHDN In shutdown mode, the NGATE pin is held low. V (Pin 5): Supply Pin. Must be closely decoupled to CC GND (Pin 2): Ground Pin. GND (Pin 2). V (Pin 3): Receives the feedback voltage from an external NGATE (Pin 6): Gate Drive for the External N-channel FB resistive divider across the output. MOSFET. This pin swings from 0V to V . CC BLOCK DIAGRAM 5 VCC SHUTDOWN COMPARATOR 0.3μA 0.28V + VCC VCC < VTURNON UNDERVOLTAGE SHUNT LOCKOUT 800mV REGULATOR – REFERENCE SOFT- SHUTDOWN START CLAMP CURRENT ERROR – COMPARATOR VCC + AMPLIFIER SWITCHING GATE R LOGIC AND DRIVER NGATE 3 VFB – + S Q BCLIARNCKUIINTG 6 SLOPE 20mV COMP GND 1.2V 200kHz CURRENT 2 OSCILLATOR RAMP SENSE 4 ITH/RUN 1 38035 BD 38035fd 6

LTC3803-5 OPERATION The LTC3803-5 is a constant frequency current mode voltage regulation loop is closed. For example, whenever controller for fl yback, SEPIC and DC/DC boost converter the load current increases, output voltage will decrease applications in a tiny ThinSOT package. The LTC3803-5 is slightly, and sensing this, the error amplifi er raises the designed so that none of its pins need to come in contact I /RUN voltage by sourcing current into the I /RUN pin, TH TH with the input or output voltages of the power supply circuit raising the current comparator threshold, thus increasing of which it is a part, allowing the conversion of voltages well the peak currents through the transformer primary and beyond the LTC3803-5’s absolute maximum ratings. secondary. This delivers more current to the load, bringing the output voltage back up. Main Control Loop The I /RUN pin serves as the compensation point for TH Due to space limitations, the basics of current mode DC/DC the control loop. Typically, an external series RC network conversion will not be discussed here; instead, the reader is connected from I /RUN to ground and is chosen for TH is referred to the detailed treatment in Application Note optimal response to load and line transients. The impedance 19, or in texts such as Abraham Pressman’s Switching of this RC network converts the output current of the error Power Supply Design. amplifi er to the I /RUN voltage which sets the current TH comparator threshold and commands considerable infl u- Please refer to the Block Diagram and the Typical Ap- ence over the dynamics of the voltage regulation loop. plication on the front page of this data sheet. An external resistive voltage divider presents a fraction of the output Start-Up/Shutdown voltage to the V pin. The divider must be designed so FB that when the output is at the desired voltage, the V pin The LTC3803-5 has two shutdown mechanisms to disable FB voltage will equal the 800mV from the internal reference. and enable operation: an undervoltage lockout on the V CC If the load current increases, the output voltage will de- supply pin voltage, and a forced shutdown whenever ex- crease slightly, causing the V pin voltage to fall below ternal circuitry drives the I /RUN pin low. The LTC3803-5 FB TH 800mV. The error amplifi er responds by feeding current transitions into and out of shutdown according to the state into the I /RUN pin. If the load current decreases, the diagram (Figure 1). TH V voltage will rise above 800mV and the error amplifi er FB will sink current away from the I /RUN pin. TH The voltage at the I /RUN pin commands the pulse-width TH LTC3803-5 modulator formed by the oscillator, current comparator SHUT DOWN and RS latch. Specifi cally, the voltage at the I /RUN pin TH sets the current comparator’s trip threshold. The current comparator monitors the voltage across a current sense resistor in series with the source terminal of the external (NVOCMC I<N VATLULRYN 4OVFF) V(NITOHM/RIUNNA L<L VYIT 0H.S2H8DVN) VAINTDH/ RVUCNC >> VVTITUHRSNHODNN (NOMINALLY 4.8V) MOSFET. The LTC3803-5 turns on the external power MOSFET when the internal free-running 200kHz oscillator sets the RS latch. It turns off the MOSFET when the cur- rent comparator resets the latch or when 80% duty cycle LTC3803-5 ENABLED is reached, whichever happens fi rst. In this way, the peak current levels through the fl yback transformer’s primary 38035 F01 and secondary are controlled by the I /RUN voltage. TH Figure 1. Start-Up/Shutdown State Diagram Since the I /RUN voltage is increased by the error ampli- TH fi er whenever the output voltage is below nominal, and decreased whenever output voltage exceeds nominal, the 38035fd 7

LTC3803-5 OPERATION The undervoltage lockout (UVLO) mechanism prevents Powering the LTC3803-5 the LTC3803-5 from trying to drive a MOSFET with in- In the simplest case, the LTC3803-5 can be powered from suffi cient V . The voltage at the V pin must exceed GS CC a high voltage supply through a resistor. A built-in shunt V (nominally 4.8V) at least momentarily to enable TURNON regulator from the V pin to GND will draw as much CC LTC3803-5 operation. The V voltage is then allowed to CC current as needed through this resistor to regulate the fall to V (nominally 4V) before undervoltage lockout TURNOFF V voltage to around 8.1V as long as the V pin is not CC CC disables the LTC3803-5. forced to sink more than 25mA. This shunt regulator is The I /RUN pin can be driven below V (nominally always active, even when the LTC3803-5 is in shutdown, TH ITHSHDN 0.28V) to force the LTC3803-5 into shutdown. An internal since it serves the vital function of protecting the V pin CC 0.3μA current source always tries to pull this pin towards from seeing too much voltage. V . When the I /RUN pin voltage is allowed to exceed CC TH The V pin must be bypassed to ground immediately ad- CC V , and V exceeds V , the LTC3803-5 ITHSHDN CC TURNON jacent to the IC pins with a ceramic or tantalum capacitor. begins to operate and an internal clamp immediately Proper supply bypassing is necessary to supply the high pulls the I /RUN pin up to about 0.7V. In operation, the TH transient currents required by the MOSFET gate driver. I /RUN pin voltage will vary from roughly 0.7V to 1.9V TH 10μF is a good starting point. to represent current comparator thresholds from zero to maximum. Adjustable Slope Compensation Internal Soft-Start The LTC3803-5 injects a 5μA peak current ramp out through its SENSE pin which can be used for slope compensation in An internal soft-start feature is enabled whenever the designs that require it. This current ramp is approximately LTC3803-5 comes out of shutdown. Specifi cally, the I / TH linear and begins at zero current at 6.5% duty cycle, reach- RUN voltage is clamped and is prevented from reaching ing peak current at 80% duty cycle. Additional details are maximum until roughly 0.7ms has passed. This allows provided in the Applications Information section. the input and output currents of LTC3803-5-based power supplies to rise in a smooth and controlled manner on start-up. 38035fd 8

LTC3803-5 APPLICATIONS INFORMATION Many LTC3803-5 application circuits can be derived from Choose resistance values for R1 and R2 to be as large as the topology shown in Figure 2. possible in order to minimize any effi ciency loss due to the static current drawn from V , but just small enough The LTC3803-5 itself imposes no limits on allowed power OUT so that when V is in regulation, the error caused by output, input voltage V or desired regulated output voltage OUT IN the nonzero input current to the V pin is less than 1%. V ; these are all determined by the ratings on the external FB OUT A good rule of thumb is to choose R1 to be 80k or less. power components. The key factors are: Q1’s maximum drain-source voltage (BV ), on-resistance (R ) DSS DS(ON) and maximum drain current, T1’s saturation fl ux level and TRANSFORMER DESIGN CONSIDERATIONS winding insulation breakdown voltages, C and C ’s IN OUT Transformer specifi cation and design is perhaps the most maximum working voltage, ESR, and maximum ripple critical part of applying the LTC3803-5 successfully. In current ratings, and D1 and R ’s power ratings. SENSE addition to the usual list of caveats dealing with high fre- quency power transformer design, the following should VIN D1 prove useful. T1 VOUT • RVCC CIN LPRI LSEC COUT Turns Ratios • Due to the use of the external feedback resistor divider CVCC 5 ratio to set output voltage, the user has relative freedom VCC 1 6 ITH/RUN NGATE Q1 in selecting transformer turns ratio to suit a given appli- CC 2 LTC3803-5 4 RSL cation. Simple ratios of small integers, e.g., 1:1, 2:1, 3:2, GND SENSE etc. can be employed which yield more freedom in setting VFB RSENSE total turns and mutual inductance. Simple integer turns 3 R1 R2 ratios also facilitate the use of “off-the-shelf” confi gu- 38035 F02 rable transformers such as the Coiltronics VERSA-PAC™ Figure 2. Typical LTC3803-5 Application Circuit series in applications with high input to output voltage ratios. For example, if a 6-winding VERSA-PAC is used SELECTING FEEDBACK RESISTOR DIVIDER VALUES with three windings in series on the primary and three windings in parallel on the secondary, a 3:1 turns ratio The regulated output voltage is determined by the resistor will be achieved. divider across V (R1 and R2 in Figure 2). The ratio OUT of R2 to R1 needed to produce a desired VOUT can be Turns ratio can be chosen on the basis of desired duty calculated: cycle. However, remember that the input supply voltage plus the secondary-to-primary referred version of the V –0.8V R2= OUT (cid:129)R1 fl yback pulse (including leakage spike) must not exceed 0.8V the allowed external MOSFET breakdown rating. 38035fd 9

LTC3803-5 APPLICATIONS INFORMATION Leakage Inductance For example, a peak switch current of 5A requires a sense resistor of 0.020Ω. Note that the instantaneous peak power Transformer leakage inductance (on either the primary in the sense resistor is 0.5W and it must be rated accord- or secondary) causes a voltage spike to occur after the ingly. The LTC3803-5 has only a single sense line to this output switch (Q1) turn-off. This is increasingly prominent resistor. Therefore, any parasitic resistance in the ground at higher load currents, where more stored energy must side connection of the sense resistor will increase its ap- be dissipated. In some cases a “snubber” circuit will be parent value. In the case of a 0.020Ω sense resistor, one required to avoid overvoltage breakdown at the MOSFET’s milliohm of parasitic resistance will cause a 5% reduction drain node. Application Note 19 is a good reference on in peak switch current. So the resistance of printed circuit snubber design. copper traces and vias cannot necessarily be ignored. A bifi lar or similar winding technique is a good way to minimize troublesome leakage inductances. However, PROGRAMMABLE SLOPE COMPENSATION remember that this will limit the primary-to-secondary breakdown voltage, so bifi lar winding is not always The LTC3803-5 injects a ramping current through its SENSE practical. pin into an external slope compensation resistor (RSL in Figure 2). This current ramp starts at zero right after the NGATE pin has been high for the LTC3803-5’s minimum CURRENT SENSE RESISTOR CONSIDERATIONS duty cycle of 6.5%. The current rises linearly towards a The external current sense resistor (RSENSE in Figure 2) peak of 5μA at the maximum duty cycle of 80%, shutting allows the user to optimize the current limit behavior for off once the NGATE pin goes low. A series resistor (R ) SL the particular application. As the current sense resistor connecting the SENSE pin to the current sense resistor is varied from several ohms down to tens of milliohms, (R ) thus develops a ramping voltage drop. From SENSE peak switch current goes from a fraction of an ampere to the perspective of the SENSE pin, this ramping voltage several amperes. Care must be taken to ensure proper adds to the voltage across the sense resistor, effectively circuit operation, especially with small current sense reducing the current comparator threshold in proportion resistor values. 38035fd 10

LTC3803-5 APPLICATIONS INFORMATION to duty cycle. This stabilizes the control loop against GND to drop enough voltage across RVCC to regulate subharmonic oscillation. The amount of reduction in the VCC to around 8.1V. For applications where VIN is low current comparator threshold (ΔVSENSE) can be calculated enough such that the static power dissipation in RVCC is using the following equation: acceptable, using the VCC shunt regulator is the simplest way to power the LTC3803-5. DutyCycle–6.5% ΔV = (cid:129)5μA(cid:129)R SENSE SL 73.5% EXTERNAL PREREGULATOR Note: LTC3803-5 enforces 6.5% < Duty Cycle < 80%. The circuit in Figure 4 shows another way to power the A good starting value for R is 5.9k, which gives a 30mV LTC3803-5. An external series preregulator consisting SL drop in current comparator threshold at 80% duty cycle. of series pass transistor Q1, Zener diode D1, and bias Designs not needing slope compensation may replace resistor RB brings VCC above the VCC turn-on threshold, R with a short circuit. enabling the LTC3803-5. SL 8V TO VCC SHUNT REGULATOR 75 VIN An internal shunt regulator allows the LTC3803-5 to be powered through a single dropping resistor from VIN to R10B0k QM1MBTA42 LTC3803-5 V , in conjunction with a bypass capacitor, C , that VCC CC VCC closely decouples VCC to GND (see Figure 3). The shunt D6.18V C0.V1CμCF GND regulator can draw up to 25mA through the V pin to CC 38035 F04 VIN Figure 4. Powering the LTC3803-5 RVCC LTC3803-5 with an External Preregulator VCC CVCC GND 38035 F03 Figure 3. Powering the LTC3803-5 Via the Internal Shunt Regulator 38035fd 11

LTC3803-5 TYPICAL APPLICATIONS 2W Isolated Housekeeping Telecom Converter BAS516 PRIMARY SIDE 10V, 100mA OUTPUT 220k T1 • MMBTA42 2.2μF PDZ6.8B 130Ω 1μF BAS516 VIN 36V TO 75V • SECONDARY SIDE 2.2μF 10V, 100mA BAS516 9.09k 1k • OUTPUT SECONDARY SIDE GROUND 1nF 22k 1 LTC3803-5 6 ITH/RUN NGATE FDC2512 2 5 GND VCC T1: PULSE ENGINEERING PA0648 787Ω 3 4 5.6k OR TYCO TTI8698 VFB SENSE 1μF 0.1Ω PRIMARY GROUND 38035 TA03 38035fd 12

LTC3803-5 TYPICAL APPLICATIONS 4:1 Input Range 3.3V Output Isolated Flyback DC/DC Converter T1 VIN+ PA1277NL V3.O3UVT+ 18 V TO 72V • 100μF 3A VIN– 2.2μF 220k MMBTA42 • PDS1040 6×. 33V GND 68Ω BAS516 PDZ6.8B 130Ω 150pF VCC 10Ω 680Ω 22Ω BAS516 • 1 6 0.1μF ITH/RUN GATE FDC2512 2 GNDLTC3803-5VCC 5 VOUT+ 3 4 4.7k VFB SENSE BAT760 0.1μF 0.040Ω VCC 270Ω 6.8k 1 6 VOUT+ BAS516 PS2801-1 1 0.1μF 2 VINLT443O0PTO 5 2.2nF 56k 47pF GND COMP 2 0.33μF3 4 100k OC FB BAS516 22.1k 38035 TA05 Effi ciency vs Load Current 84 82 80 %) Y ( 78 C N E CI 76 EFFI 74 72 VIN = 48V VIN = 24V 70 0 1 2 3 4 IOUT (A) 38035 TA05a 38035fd 13

LTC3803-5 PACKAGE DESCRIPTION S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 2.90 BSC 0.62 0.95 (NOTE 4) MAX REF 1.22 REF 1.50 – 1.75 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT 0.30 – 0.45 0.95 BSC PER IPC CALCULATOR 6 PLCS (NOTE 3) 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 1.90 BSC 0.09 – 0.20 (NOTE 3) S6 TSOT-23 0302 REV B NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 38035fd 14

LTC3803-5 REVISION HISTORY (Revision history begins at Rev D) REV DATE DESCRIPTION PAGE NUMBER D 6/10 MP-grade part added. Refl ected throughout the data sheet. 1 to 16 38035fd Information furnished by Linear Technology Corporation is believed to be accurate and reliable. 15 However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

LTC3803-5 TYPICAL APPLICATION Synchronous Flyback Converter VIN 36V TO 72V 220k MMBTA42 CIN T1 V3.O3UVT* • Q2 1.5A CO PDZ6.8B • 130Ω 1n D1 33k 1 6 ITH/RUN GATE Q1 • 2 LTC3803-5 5 560 0.1μF GND VCC 8.06k 3 4 5k VFB SENSE 25.5k* RFB 11μ0FV RCS 38035 TA04 VOUT T1: PULSE ENGINEERING PA1006 D1: PHILIPS BAS516 RCS: VISHAY OR IRC, 80mΩ Q1: FAIRCHILD FDC2512 CIN: TDK 1μF, 100V, X5R *FOR 5V OUTPUT CHANGE Q2: VISHAY Si9803 CO: TDK 100μF, 6.3V, X5R RFB TO 42.2k RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT3573 Isolated Flyback Switching Regulator with 60V 3V ≤ V ≤ 40V, No Opto-Isolator or Third Winding Required, Up to 7W IN Integrated Switch Output Power, MSOP-16E LTC3805/ Adjustable Constant Frequency Flyback, Boost, SEPIC V and V Limited Only by External Components, 3mm × 3mm DFN-10, IN OUT LTC3805-5 DC/DC Controller MSOP-10E Packages LTC3873/ No R ™ Constant Frequency Flyback, Boost, SEPIC V and V Limited Only by External Components, 8-pin ThinSOT or SENSE IN OUT LTC3873-5 Controller 2mm × 3mm DFN-8 Packages LT3757 Boost, Flyback, SEPIC and Inverting Controller 2.9V ≤ V ≤ 40V, 100kHz to 1MHz Programmable Operating Frequency, IN 3mm × 3mm DFN-10 and MSOP-10E Package LT3758 Boost, Flyback, SEPIC and Inverting Controller 5.5V ≤ V ≤ 100V, 100kHz to 1MHz Programmable Operating Frequency, IN 3mm × 3mm DFN-10 and MSOP-10E LTC1871/LTC1871-1/ Wide Input Range, No R Low Quiescent Current Programmable Operating Frequency, 2.5V ≤ V ≤ 36V, Burst Mode® SENSE IN LTC1871-7 Flyback, Boost and SEPIC Controller Operation at Light Load, MSOP-10 38035fd 16 Linear Technology Corporation LT 0610 REV D • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004