LT3001

LT3001 (Rev. 0)

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 10

Technical content

Rev. 0For more information www.analog.comDocument Feedback TYPICAL APPLICATION FEATURES DESCRIPTION 36V 4W No-Opto Isolated Flyback Converter The LT®3001 is a micropower isolated flyback converter . By sampling the isolated output voltage directly from the primary-side flyback waveform, the part requires no third winding or opto-isolator for regulation. The output voltage is programmed with a single external resistor . Internal compensation and soft-start further reduce external com- ponent count. Boundary mode operation provides a small magnetic solution with excellent load regulation. Low ripple Burst Mode operation maintains high efficiency at light load while minimizing the output voltage ripple. A 1.2A, 65V DMOS power switch is integrated along with all high voltage circuitry and control logic into a 5-lead ThinSOT™ package. The LT3001 operates from an input voltage range of 4V to 36V and can deliver up to 4W of isolated output power . The high level of integration and the use of boundary and low ripple burst modes result in a simple to use, low component count, and high efficiency application solution for isolated power delivery. All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. Patents, including 5438499, 7463497, and 7471522. 4V to 36VIN/5VOUT Micropower Isolated Flyback Converter

APPLICATIONS

n 4V to 36V Input Voltage Range n 1.2A, 65V Internal DMOS Power Switch n Low Quiescent Current n Boundary Mode Operation at Heavy Load n Low-Ripple Burst Mode® Operation at Light Load n Minimum Load <0.5% (Typ) of Full Output n VOUT Set with a Single External Resistor n No T ransformer Third Winding or Opto-Isolator Required for Regulation n Accurate EN/UVLO Threshold and Hysteresis n Internal Compensation and Soft-Start n Output Short-Circuit Protection n 5-Lead TSOT-23 Package n Isolated Telecom, Automotive, Industrial, Medical Power Supplies n Isolated Auxiliary/Housekeeping Power Supplies Efficiency vs Load Current LT3001 3:1 RFB SW 40µH 4.4µH EN/UVLO 10µF VIN VIN 4V TO 36V VOUT+ 6mA TO 0.40A (VIN = 5V) 6mA TO 0.70A (VIN = 12V) 6mA TO 1.00A (VIN = 24V) 6mA TO 1.15A (VIN = 36V) VOUT– GND 154k 100µF

3001 TA01a

LOAD CURRENT (A) EFFICIENCY (%) 0.2 0.4 0.6 0.8

3001 TA01b

1.0 1.2 VIN = 5V VIN = 12V VIN = 24V VIN = 36V

Rev. 0 For more information www.analog.com PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS Operating Junction Temperature Range (Notes 3, 4) (Note 1) EN/UVLO 1 GND 2 TOP VIEW S5 PACKAGE 5-LEAD PLASTIC TSOT-23 θJA = 215°C/W RFB 3

5 VIN

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3001ES5#TRMPBF LT3001ES5#TRPBF L THMF 5-Lead Plastic TSOT-23 –40°C to 125°C LT3001IS5#TRMPBF LT3001IS5#TRPBF L THMF 5-Lead Plastic TSOT-23 –40°C to 125°C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.

Rev. 0For more information www.analog.com

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 SW pin is rated to 65V for transients. Depending on the leakage inductance voltage spike, operating waveforms of the SW pin should be derated to keep the flyback voltage spike below 65V. The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VEN/UVLO = VIN unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNIT VIN Input Voltage Range 4 36 V IQ VIN Quiescent Current VEN/UVLO = 0.2V Active Mode 0.8 350 2 µA µA EN/UVLO Shutdown Threshold For Lowest Off IQ 0.2 0.55 V EN/UVLO Enable Threshold Falling Hysteresis 1.204 1.228 0.014 1.248 V V IHYS EN/UVLO Hysteresis Current VEN/UVLO = 1.1V VEN/UVLO = 1.3V 2.2 –0.1 2.5 2.8 0.1 µA µA fMIN Minimum Switching Frequency 9.4 10 10.6 kHz tON(MIN) Minimum Switch-On Time 170 ns ISW(MAX) Maximum SW Current Limit 1.200 1.375 1.550 A ISW(MIN) Minimum SW Current Limit 0.22 0.29 0.36 A RDS(ON) Switch On-Resistance ISW = 500mA 0.4 Ω IRFB RFB Regulation Current l 97.5 100 102.5 µA Note 3: The LT3001E is guaranteed to meet performance specifications from 0°C to 125°C operating junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3001I is guaranteed over the full –40°C to 125°C operating junction temperature range. Note 4: The LT3001 includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 150°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability.

Rev. 0 For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Boundary Mode Waveforms Discontinuous Mode Waveforms Burst Mode Waveforms EN/UVLO Enable Threshold RFB Regulation Current Switch Current Limit Output Load and Line Regulation Output Short-Circuit Protection Switching Frequency vs Load Current TA = 25°C, unless otherwise noted. LOAD CURRENT (A) 350 300 250 200 150 100 0.6 1.0

3001 G03

0.2 0.4 0.8 1.2 SWITCHING FREQUENCY (kHz) VIN = 5V VIN = 12V VIN = 24V VIN = 36V FRONT PAGE APPLICATION TEMPERATURE (°C) VEN/UVLO (V) 1.245 1.210 1.215 1.230 1.235 1.240 1.220 1.225 1.205

3001 G10

1507550 125100250–25–50 TEMPERATURE (°C) IRFB (µA) 105 101 102 103 104 100

3001 G12

1507550 125100250–25–50 TEMPERATURE (°C) –50 ISW (A)0.8 1.2 150

3001 G14

0.4 0 50 100–25 25 75 125 1.6 0.6 1.0 0.2

1.4 MAXIMUM CURRENT LIMIT

LOAD CURRENT (A) OUTPUT VOLTAGE (V) 5.00

3001 G01

4.90 4.80 5.10

5.20 FRONT PAGE APPLICATION

4.95 4.85 5.05 5.15 1.2 VIN = 5V VIN = 12V VIN = 24V VIN = 36V LOAD CURRENT (A) OUTPUT VOLTAGE (V) 0.4 0.8 1.2 1.6

3001 G02

0.2 0.6 1.0 1.4 VIN = 5V VIN = 12V VIN = 24V VIN = 36V FRONT PAGE APPLICATION VOUT 50mV/DIV VSW 20V/DIV 5µs/DIV FRONT PAGE APPLICATION VIN = 12V ILOAD = 600mA

3001 G04

5µs/DIV FRONT PAGE APPLICATION VIN = 12V ILOAD = 200mA

3001 G05

20µs/DIV FRONT PAGE APPLICATION VIN = 12V ILOAD = 6mA

3001 G06

Rev. 0For more information www.analog.com PIN FUNCTIONS EN/UVLO (Pin 1) : Enable/Undervoltage Lockout. The EN/UVLO pin is used to enable the LT3001. Pull the pin below 0.2V to shut down the LT3001. This pin has an accurate 1.228V threshold and can be used to program a VIN undervoltage lockout (UVLO) threshold using a resis- tor divider from VIN to ground. A 2.5µA current hysteresis allows the programming of VIN UVLO hysteresis. If neither function is used, tie this pin directly to VIN. GND (Pin 2): Ground. Tie this pin directly to local ground plane. RFB (Pin 3) : Input Pin for External Feedback Resistor . Connect a resistor from this pin to the transformer primary SW pin. The ratio of the R FB resistor to an internal 10k resistor , times a trimmed 1.0V reference voltage, deter - mines the output voltage (plus the effect of any non-unity transformer turns ratio). Minimize trace area at this pin. SW (Pin 4) : Drain of the 65V Internal DMOS Power Switch. Minimize trace area at this pin to reduce EMI and voltage spikes. VIN (Pin 5) : Input Supply. The V IN pin supplies current to internal circuitry and serves as a reference voltage for the feedback circuitry connected to the R FB pin. Locally bypass this pin to ground with a capacitor . OPERATION The LT3001 is a current mode switching regulator IC designed specially for the isolated flyback topology. The key problem in isolated topologies is how to commu - nicate the output voltage information from the isolated secondary side of the transformer to the primary side for regulation. Historically, opto-isolators or extra trans- former windings communicate this information across the isolation boundary. Opto-isolator circuits waste output power , and the extra components increase the cost and physical size of the power supply. Opto-isolators can also cause system issues due to limited dynamic response, nonlinearity, unit-to-unit variation and aging over life - time. Circuits employing extra transformer windings also exhibit deficiencies, as using an extra winding adds to the transformer ’s physical size and cost, and dynamic response is often mediocre. The LT3001 samples the isolated output voltage through the primary-side flyback pulse waveform. In this man - ner , neither opto-isolator nor extra transformer winding is required for regulation. Since the LT3001 operates in either boundary conduction mode or discontinuous conduction mode, the output voltage is always sampled on the SW pin when the secondary current is zero. This method improves load regulation without the need of external load compensation components.

the power switch shorter than approximately 170ns. falling threshold is set at 1.228V with 14mV hysteresis. LT3001 in shutdown with quiescent current less than 2µA. Figure 1. Undervoltage Lockout (UVLO)

3001 F01

Step 1: Select the T ransformer Turns Ratio. bility at different transformer turns ratio. Table 1. Switch Voltage Stress and Output Current Capability requirement, NPS = 3 is chosen in this example. Step 2: Determine the Primary Inductance.

Rev. 0 For more information www.analog.com APPLICATIONS INFORMATION Most transformers specify primary inductance with a tol- erance of ±20%. With other component tolerance consid- ered, choose a transformer with its primary inductance 30% larger than the minimum values calculated above. LPRI = 40µH is then chosen in this example. Once the primary inductance has been determined, the maximum load switching frequency can be calculated as: fSW = 1 tON +tOFF = 1 LPRI •ISW VIN + LPRI •ISW NPS •(VOUT +VF ) ISW = VOUT •IOUT • 2 η• VIN •D Example: D = (5V +0.3V)• 3 (5V +0.3V)• 3+12V =0.57 ISW = 5V • 0.5A • 2 0.85 •12V • 0.57 =0.86A fSW =199kHz The transformer also needs to be rated for the correct saturation current level across line and load conditions. A saturation current rating larger than 2A is necessary to work with the LT3001. The 750313974 from Würth is chosen as the flyback transformer . Step 3: Choose the Output Diode. T wo main criteria for choosing the output diode include forward current rating and reverse voltage rating. The maximum load requirement is a good first-order guess as the average current requirement for the output diode. A conservative metric is the maximum switch current limit multiplied by the turns ratio, I DIODE(MAX) = ISW(MAX) • NPS Example: I DIODE(MAX) = 4.125A Next calculate reverse voltage requirement using maxi - mum VIN: VREVERSE =VOUT + VIN(MAX) NPS Example: VREVERSE =5V +32V =15.6V The CMS H5-20 ( 5A, 20V diode) from Central Semiconductor is chosen. Step 4: Choose the Output Capacitor . The output capacitor should be chosen to minimize the output voltage ripple while considering the increase in size and cost of a larger capacitor . Use the equation below to calculate the output capacitance: COUT = LPRI •ISW 2 • VOUT • ΔVOUT Example: Design for output voltage ripple less than 1% of V OUT, i.e., 50mV. COUT = 40µH •(0.86A)2 2 • 5V • 0.05V =60µF Remember ceramic capacitors lose capacitance with applied voltage. The capacitance can drop to 40% of quoted capacitance at the maximum voltage rating. So a 100µF, 10V rating ceramic capacitor is chosen. Step 5: Design Snubber Circuit. The snubber circuit protects the power switch from leak- age inductance voltage spike. A DZ snubber is recom - mended for this application because of lower leakage inductance and larger voltage margin. The Zener and the diode need to be selected. The maximum Zener breakdown voltage is set according to the maximum VIN: V ZENER(MAX) ≤ 65V – VIN(MAX)

Rev. 0For more information www.analog.com Information furnished by Analog Devices is believed to be accurate and reliable. However , no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. APPLICATIONS INFORMATION Example: V ZENER(MAX) ≤ 65V – 32V = 33V A 20V Zener with a maximum of 21V will provide optimal protection and minimize power loss. So a 20V, 0.25W Zener from Central Semiconductor (CMDZ5250B) is chosen. Choose a diode that is fast and has sufficient reverse volt- age breakdown: V REVERSE > VSW(MAX) V SW(MAX) = VIN(MAX) + VZENER(MAX) Example: V REVERSE > 53V A 100V, 0.25A diode from Central Semiconductor (CMHD4448) is chosen. Step 6: Select the RFB Resistor . Use the following equation to calculate the starting value for RFB: RFB = NPS •(VOUT +VF ) 100µA Example: RFB = 3 •(5V +0.3V) 100µA =159k Depending on the tolerance of standard resistor values, the precise resistor value may not exist. For 1% stan - dard values, a 158k resistor should be close enough. The final RFB value should be adjusted on the measured output voltage. Step 7: Select the EN/UVLO Resistors. Determine the amount of hysteresis required and calcu - late R1 resistor value: V IN(HYS) = 2.5µA • R1 Example: Choose 2V of hysteresis, R1 = 806k Determine the UVLO thresholds and calculate R2 resistor value: VIN(UVLO+) =1.242V •(R1+R2) +2.5µA •R1 Example: Set VIN UVLO rising threshold to 7.5V, R2 = 232k V IN(UVLO+) = 7.5V V IN(UVLO–) = 5.5V Step 8: Ensure minimum load. The theoretical minimum load can be approximately esti- mated as: ILOAD(MIN) = 40µH •(360mA)2 •10.6kHz 2 • 5V =5.5mA Remember to check the minimum load requirement in real application. The minimum load occurs at the point where the output voltage begins to climb up as the con - verter delivers more energy than what is consumed at the output. The real minimum load for this application is about 6mA. In this example, a 820Ω resistor is selected as the minimum load.

Rev. 0 For more information www.analog.com  ANALOG DEVICES, INC. 2019 www.analog.com PACKAGE DESCRIPTION 1.50 – 1.75 (NOTE 4)2.80 BSC 0.30 – 0.45 TYP

5 PLCS (NOTE 3)

DATUM ‘A’ 0.09 – 0.20 (NOTE 3) S5 TSOT-23 0302 REV B PIN ONE

2.90 BSC

(NOTE 4)

0.95 BSC

1.90 BSC

0.80 – 0.90

1.00 MAX

0.01 – 0.100.20 BSC 0.30 – 0.50 REF 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

3.85 MAX

0.62 MAX 0.95 REF RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 1.4 MIN2.62 REF

1.22 REF

(Reference LTC DWG # 05-08-1635 Rev B)