LT3575IFE#PBF Linear Technology, LT3575IFE#PBF Datasheet

Page 1

... Off the shelf transformers are available for many applications. L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks and No RSENSE and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. ...

Page 2

... LEAD FREE FINISH TAPE AND REEL LT3575EFE#PBF LT3575EFE#TRPBF LT3575IFE#PBF LT3575IFE#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. *The temperature grade is identifi label on the shipping container. For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T PARAMETER I Reference Current REF Error Amplifi er Voltage Gain Error Amplifi er Transconductance Minimum Switching Frequency TC Current into R REF BIAS Pin Voltage Note 1: Stresses beyond those ...

Page 4

LT3575 TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage 500 450 400 25°C 350 125°C 300 250 –50°C 200 150 100 500 1000 1500 2000 2500 SWITCH CURRENT (mA) 3575 G04 SHDN/UVLO Falling Threshold 1.28 1.26 1.24 1.22 1.20 ...

Page 5

PIN FUNCTIONS NC (Pins 1, 15, 16): No Connect Pins. Can be left open or connected to any ground plane. V (Pin 2): Input Voltage. This pin supplies current to IN the internal start-up circuitry and as a reference voltage ...

Page 6

LT3575 BLOCK DIAGRAM CURRENT REF R4 BIAS C5 1.22V R1 SHDN/UVLO R2 2.8μ FLYBACK Q2 ERROR CURRENT AMP COMPARATOR – g – m ...

Page 7

OPERATION The LT3575 is a current mode switching regulator IC designed specifi cally for the isolated fl yback topology. The special problem normally encountered in such circuits is that information relating to the output voltage on the isolated secondary side ...

Page 8

LT3575 APPLICATIONS INFORMATION ERROR AMPLIFIER—PSEUDO DC THEORY In the Block Diagram, the R (R4) and R REF can be found. They are external resistors used to program the output voltage. The LT3575 operates much the same way as traditional current ...

Page 9

APPLICATIONS INFORMATION ERROR AMPLIFIER—DYNAMIC THEORY Due to the sampling nature of the feedback loop, there are several timing signals and other constraints that are required for proper LT3575 operation. Minimum Current Limit The LT3575 obtains output voltage information from the ...

Page 10

... Linear Technology has worked with several leading magnetic component manufacturers to produce pre-designed fl yback transformers for use with the LT3575. Table 5 shows the details of several of these transformers ...

Page 11

APPLICATIONS INFORMATION Table 5. Predesigned Transformers—Typical Specifi cations, Unless Otherwise Noted TRANSFORMER DIMENSION PART NUMBER ( (mm) 750311306 15.24 13.3 11.43 750311307 15.24 13.3 11.43 750311308 15.24 13.3 11.43 750310564 15.24 13.3 11.43 750311303 15.24 13.3 11.43 750311304 ...

Page 12

LT3575 APPLICATIONS INFORMATION Turns Ratio Note that when using REF output voltage, the user has relative freedom in selecting a transformer turns ratio to suit a given application.In contrast, simpler ratios of small integers, e.g., 1:1, ...

Page 13

APPLICATIONS INFORMATION CLAMP EITHER ZENER OR RC 3575 F04 Figure 4. Snubber Clamping 10V/DIV 100ns/DIV Figure 6. Good Snubber Diode Limits SW Pin Voltage V < 60V < 55V < 50V Figure 5. Maximum Voltages ...

Page 14

... The Linear Technology applications group is available and extremely qualifi assist in the selection and/or design of the transformer. Setting the Current Limit Resistor ...

Page 15

APPLICATIONS INFORMATION Minimum Load Requirement The LT3575 obtains output voltage information through the transformer while the secondary winding is conducting current. During this time, the output voltage (multiplied times the turns ratio) is presented to the primary side of the ...

Page 16

LT3575 APPLICATIONS INFORMATION The transformer turns ratio is selected such that the converter has adequate current capability and a switch stress below 50V. Table 6 shows the switch voltage stress and output current capability at different transformer turns ratio. Table ...

Page 17

APPLICATIONS INFORMATION Zener clamps. Among them, RCD is widely used. Figure 9 shows the RCD snubber in a fl yback converter. A typical switch node waveform is shown in Figure 10. During switch turn-off, the energy stored in the leakage ...

Page 18

LT3575 TYPICAL APPLICATIONS μ F 200k R2 90. 28.7k 10k μ F 200k R2 90. 10k 59k 18 Low Input Voltage 5V Isolated Flyback ...

Page 19

TYPICAL APPLICATIONS V IN 12V TO 24V C1 (*30V) 10 μ 28.7k 10k 3575 TA04 5V Isolated Flyback Converter C6 R1 0.22 μ 499k V IN SHDN/UVLO R2 D3 71.5k R3 80. LT3575 R REF ...

Page 20

LT3575 TYPICAL APPLICATIONS V IN 12V TO 24V C1 (*36V μ F 499k R2 71. 19.1k 10k 3575 TA05 20 3.3V Isolated Flyback Converter C6 0.22 μ SHDN/UVLO D3 R3 76. ...

Page 21

TYPICAL APPLICATIONS V IN 12V μ F 499k R2 71. 59k 10k 3575 TA06 12V Isolated Flyback Converter C6 0.22 μ SHDN/UVLO D2 LT3575 178k R REF R4 6.04k ...

Page 22

LT3575 TYPICAL APPLICATIONS V IN 12V TO 24V C1 10 μ 499k R2 71. 59k 10k 22 Four Output 12V Isolated Flyback Converter C6 0.22 μ SHDN/UVLO R3 118k LT3575 R FB ...

Page 23

... DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. FE Package 16-Lead Plastic TSSOP (4 ...

Page 24

... H 47 μ – V OUT –5V, 500mA *OPTIONAL THIRD WINDING FOR D3 >24V OPERATION L1D T1: WÜRTH ELEKTRONIK 750310564 7 H μ D4: PMEG6010 D1, D2: PDS835L 3575 TA11 Limited Only by External Components Limited Only by External Components LT 0710 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2010 3575f ...