LT1105 LINER [Linear Technology], LT1105 Datasheet

Page 1

... LT1103. The LT1103 is optimized for 15W to 100W applications. For higher power applications or additional switch current flexibility, the LT1105 is available and its totem pole output drives the gate of an external FET. Unique design of the LT1103/LT1105 eliminates the need for an optocoupler while still providing 1% load and line regulation in a magnetic flux-sensed converter ...

Page 2

... No external current sense resistor is necessary with LT1103 because it is integrated with the high current switch. The LT1105 brings out the input to the current limit amplifier and requires the use of an external sense resistor. The LT1103/LT1105 have unique features not found on other offline switching regulators ...

Page 3

... After Device Has Started IN V < V Start Threshold IN IN Industrial Grade Note: Switching Stops When V < 10V (LT1103) SW Note: Switching Stops When V < 10V (LT1105) GATE 10V < V < 30V IN 0mA < I < 20mA L Commercial Grade Industrial Grade Commercial Grade Industrial Grade 17 < ...

Page 4

... V Current Limit (LT1103) SW Output Switch On Resistance (LT1103 Increase During Switch On Time (LT1103) SW Switch Output High Level (LT1105) Switch Output High Level Industrial Grade unless otherwise noted. A CONDITONS Open 40kHz 25mA, C OSC SW Note: Maximum Duty Cycle Can Be Altered at OSC Pin ...

Page 5

... DC > 35% due to internal slope compensation circuity. The LT1103 switch current limit is given by I Note 5: The current limit threshold voltage is constant for DC < 35% and decreases for DC > 35% due to internal slope compensation circuitry. The LT1105 switch current limit threshold voltage is given by V (1.7 – DC) above 35% duty cycle. pin voltage. C ...

Page 6

... LT1103/LT1105 W U TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Supply Current vs Temperature 22 21 30V –75 –50 – 100 125 150 175 TEMPERATURE (°C) LT1103 G04 V Start-Up Threshold vs IN Temperature 17.5 17.0 16.5 16.0 15.5 15.0 14.5 –75 –50 – 100 125 150 ...

Page 7

... Gate Bias Reference vs Temperature 16.2 15.8 15.4 15.0 14.6 14.2 13.8 – 100 125 150 175 –75 –50 TEMPERATURE (°C) LT1103 G20 LT1103/LT1105 Soft-Start Reset Current vs Temperature –75 – 100 125 175 – 150 TEMPERATURE (°C) LT1103 G15 5V Line Regulation vs Temperature 0 ...

Page 8

... LT1103/LT1105 W U TYPICAL PERFORMANCE CHARACTERISTICS 15V Gate Bias Short-Circuit Current vs Temperature 130 110 –75 –50 – 100 125 150 TEMPERATURE ( C) LT1103 G22 Feedback Threshold vs Temperature 4.60 4.56 4.52 4.48 4.44 4.40 –75 –50 – 100 125 150 175 TEMPERATURE (°C) LT1103 G25 ...

Page 9

... LT1103 V Current Limit vs SW Duty Cycle 3.0 –55°C 2.5 25°C 125°C 2.0 1.5 1.0 0 DUTY CYCLE (%) LT1103/LT1105 Error Amplifier High Clamp Voltage vs Temperature (FB = 4V) 4.5 4.4 4.3 4.2 4.1 4.0 150 175 –25 75 –75 – TEMPERATURE (°C) LT1103 G32 LT1103 Output Switch Leakage Current vs Temperature ...

Page 10

... LT1103 Driver Current vs Temperature –75 – 100 125 175 –50 0 150 TEMPERATURE (°C) LT1103 G41 LT1105 Current Limit Threshold Voltage vs Temperature 450 DC = 25°C 425 400 375 350 325 300 – 100 125 150 175 –75 –50 TEMPERATURE (° ...

Page 11

... NPN power switch. This pin has a typical ON resistance of 0.4 and a minimum breakdown voltage of 50V. This pin also ties to the FET gate drive detection circuit. C LT1105 All functions on the LT1105 are equivalent to the LT1103 of 0.012 mhos with the exception of the V m availability of the OVLO, 5V, and SS functions. ...

Page 12

... LT1103/LT1105 W BLOCK DIAGRA S 15V GATE 15V BIAS START-UP 16V REF FB 0VLO 2.5V 12 LT1103 OSC GATE BIAS DETECT OSCILLATOR LOGIC COMP 4.5V + – SAMPLING ERROR AMP g = 0.012 m SHUT DOWN OVERVOLTAGE 0.15V LOCKOUT V SW DRIVER SPIKE BLANK ANTISAT CURRENT LIMIT + AMP 0. – ...

Page 13

... V REF FB 0VLO 2.5V LT1105 OSC GATE BIAS DETECT OSCILLATOR LOGIC COMP 4.5V + – SAMPLING ERROR AMP g = 0.012 m SHUT DOWN OVERVOLTAGE 0.15V LOCKOUT LT1103/LT1105 DRIVER DRIVER SPIKE BLANK ANTISAT CURRENT LIMIT + I AMP – RESET LT1105 GND LIM ...

Page 14

... LT1103 in a prestart mode. LT1105 The LT1105 is a current mode switcher. Switch duty cycle is controlled by switch current rather than directly by output voltage. Referring to the block diagram, the switch is turned on at the start of each oscillator cycle turned off when switch current reaches a predetermined level ...

Page 15

... Switch duty cycle goes to zero if the V a diode, placing the LT1105 in an idle mode. Pulling the V pin below 0.15V causes total regulator shutdown and places the LT1105 in prestart mode. The SS pin implements soft-start with one external capaci- tor to ground ...

Page 16

... This allows the power supply to come up to voltage in a controlled manner and charge the output capacitor without activating current limit. In general, soft-start is not required on the LT1105 due to the design of the sampling error amplifier g stage which generates asymmetrical slew capability m ...

Page 17

... The LT1105 8-pin PDIP has Pin 1 as its ground. The LT1105 14-pin PDIP has Pin 1 and Pin 7 as grounds and must be tied together for proper operation. ...

Page 18

... EMI to a minimum. Grounding techniques are illustrated in the Typical Applications section. Oscillator The oscillator of the LT1103/LT1105 is a linear ramp type powered from the internal 6V bias line. The charging currents and voltage thresholds are generated internally so that only one external capacitor is required to set the frequency ...

Page 19

... IN for reverse base emitter voltage drive. , thereby limiting Gate Biasing (LT1105) IN The LT1105 is designed to drive an external power MOSFET in the common source configuration with the totem-pole output V SW flexibility (limited only by the choice of external power is less than SW FET) and higher output power applications than allowed by LT1103 ...

Page 20

... IN V Output (LT1105) SW The V pin of the LT1105 is the output totem-pole SW driver stage. This output stage turns an external power MOSFET on by pulling its gate high. Break-Before-Make action of 200ns is built into each switch edge to eliminate cross-conduction currents. Fast switching times and high ...

Page 21

... Vf is the forward voltage of the output diode the current flowing in the secondary, R equivalent secondary parasitic impedance and N1 is the transformer turns ratio from the secondary to the bias winding apparent that even though the above point in LT1103/LT1105 • R OUT P ...

Page 22

... LT1103/LT1105 U U APPLICATIONS INFORMATION Flyback Waveform for Continuous Mode Operation )[L(lk )]/V PRI PRI SNUB Flyback Waveform for Discontinuous Mode Operation V ZENER PRIMARY SWITCH VOLTAGE [ • R )]/N OUT SEC AREA “a” = AREA “b” TO MAINTAIN ...

Page 23

... LT1103/LT1105. The switch current is proportional to the load current by the turns ratio of the transformer. A small current proportional to switch current is generated in the LT1103/LT1105 and fed back to the FB pin. This allows the input bias current of the sampling error amplifier function of load current ...

Page 24

... Many hours spent on breadboards have shown that the simplest way to optimize the frequency compensation of the LT1103/LT1105 is to use transient response techniques and an “RC” box to quickly iterate toward the final compensation network. Additional information on this technique of frequency compensation can be found in Linear Technology’ ...

Page 25

... Vf = Forward voltage of the output diode V = Maximum switch voltage Snubber clamp level – primary flyback SNUB voltage. In the isolated flyback mode, the LT1103/LT1105 sense and regulate the transformer primary voltage V “switch off” time. The secondary output voltage will be regulated regulated. V PRI PRI V ...

Page 26

... Finally, an extra winding closely coupled to the output inductor L1 can sense the flux in this element and give a representation of the output LT1103 AI02 voltage when S1 is off. LT1103 FET Connection 15V LT1103 V SW LT1105 FET Connection 15V V LT1105 SW I LIM LT1103 TA04 LT1103 TA03 ...

Page 27

... • • 100 A 3.25V 100 • 1 – OSC 9 2.5V f OSC LT1103/LT1105 Setting Overvoltage Lockout OVLO TH R2 LT1105 OVLO R1 LT1103 TA09 CHOOSE OVLO TH LET OVLO –1 R1 2.5V Synchronizing Oscillator Frequency to an External Clock LT1103/LT1105 500ns 5V OSC 1:0 ...

Page 28

... WINDING OUTPUT SEPARATE GROUND PATH SWITCH CURRENT PATH KEEP RESISTANCE LOW 15V V IN OSC GND LT1103 TA11b TO BIAS WINDING OUTPUT LT1105 Ground Connections HIGH CURRENT GROUND PATH V GND SW I LIM BIAS LT1103 TA12a WINDING OUTPUT GND ...

Page 29

... PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) (10.160 0.255 0.015* (6.477 0.381 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.100 0.010 (2.540 0.254) LT1103/LT1105 0.400* MAX 0.130 0.005 (3.302 0.127) 0.125 0.020 (3.175) MIN (0.508) MIN 0.018 0.003 (0 ...

Page 30

... LT1103/LT1105 PACKAGE DESCRIPTION 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) +0.035 0.325 –0.015 +0.889 8.255 –0.381 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm Dimensions in inches (millimeters) unless otherwise noted. ...

Page 31

... LT1103/LT1105 0.165 – 0.180 (4.191 – 4.572) 0.045 – 0.055 (1.143 – 1.397) 0.620 (15.75) TYP 0.095 – 0.115 (2.413 – ...

Page 32

... LT1103/LT1105 U TYPICAL APPLICATION Minimum Parts Count Fully-Isolated Flyback 100kHz 50W Converter 85V TO 270V 220 F 385V 499 – 1000pF 100 BRIDGE RECTIFIER + BAV21 LINE FILTER BAV21 39 F 16.2k 1% 5.36k 1% Danger!! Lethal Voltages Present – See Text RELATED PARTS PART NUMBER DESCRIPTION LT1241 ...