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LT1945 Dataheets PDF



Part Number LT1945
Manufacturers Linear Technology
Logo Linear Technology
Description Dual Micropower DC/DC Converter
Datasheet LT1945 DatasheetLT1945 Datasheet (PDF)

FEATURES n Generates Well-Regulated Positive and Negative Outputs n Low Quiescent Current: 20μA in Active Mode (per Converter) <1μA in Shutdown Mode n Operates with VIN as Low as 1.2V n Low VCESAT Switch: 250mV at 300mA n Uses Small Surface Mount Components n High Output Voltage: Up to ±34V n Tiny 10-Pin MSOP Package APPLICATIONS n Small TFT LCD Panels n Handheld Computers n Battery Backup n Digital Cameras LT1945 Dual Micropower DC/DC Converter with Positive and Negative Outputs DESCRIPTION Th.

  LT1945   LT1945



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FEATURES n Generates Well-Regulated Positive and Negative Outputs n Low Quiescent Current: 20μA in Active Mode (per Converter) <1μA in Shutdown Mode n Operates with VIN as Low as 1.2V n Low VCESAT Switch: 250mV at 300mA n Uses Small Surface Mount Components n High Output Voltage: Up to ±34V n Tiny 10-Pin MSOP Package APPLICATIONS n Small TFT LCD Panels n Handheld Computers n Battery Backup n Digital Cameras LT1945 Dual Micropower DC/DC Converter with Positive and Negative Outputs DESCRIPTION The LT®1945 is a dual micropower DC/DC converter in a 10-pin MSOP package. Each converter is designed with a 350mA current limit and an input voltage range of 1.2V to 15V, making the LT1945 ideal for a wide variety of applications. Both converters feature a quiescent current of only 20μA at no load, which further reduces to 0.5μA in shutdown. A current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. The 36V switch allows high voltage outputs up to ±34V to be easily generated without the use of costly transformers. The LT1945’s low off-time of 400ns permits the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space-conscious portable applications. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Dual Output (+12V, –20V) Converter VIN 2.7V TO 5V C1 4.7μF L1 10μH C4 0.1μF D1 8 10 VIN 2 SHDN1 SW1 1 NFB1 LT1945 4 SHDN2 5 FB2 GND PGND PGND SW2 37 96 D2 100pF 365k 24.9k –20V 10mA C2 1μF L2 10μH C1: TAIYO YUDEN JMK212BJ475 C2, C3: TAIYO YUDEN TMK316BJ105 C4: TAIYO YUDEN EMK107BJ104 D1, D2, D3: ZETEX ZHCS400 L1, L2: MURATA LQH3C100 4.7pF D3 115k 1M C3 1μF 12V 20mA 1945 TA01 EFFICIENCY (%) 90 85 80 75 70 65 60 55 50 0.1 Efficiency at VIN = 3.6V +12V OUTPUT –20V OUTPUT 1 10 LOAD CURRENT (mA) 100 1945 TA01a 1945fa 1 LT1945 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, SHDN1, SHDN2 Voltage.....................................15V SW1, SW2 Voltage....................................................36V NFB1 Voltage ............................................................–3V FB2 Voltage............................................................... VIN Current into NFB1 Pin ............................................–1mA Current into FB2 Pin................................................1mA Junction Temperature ........................................... 125°C Operating Temperature Range (Note 2).... –40°C to 85°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C PIN CONFIGURATION NFB1 1 SHDN1 2 GND 3 SHDN2 4 FB2 5 TOP VIEW 10 SW1 9 PGND 8 VIN 7 PGND 6 SW2 MS PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 160°C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1945EMS#PBF LT1945EMS#TRPBF LTTS 10-Lead Plastic MSOP –40°C to 85°C LT1945IMS#PBF LT1945IMS#TRPBF LTTS 10-Lead Plastic MSOP –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1945EMS LT1945EMS#TR LTTS 10-Lead Plastic MSOP –40°C to 85°C LT1945IMS LT1945IMS#TR LTTS 10-Lead Plastic MSOP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified 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 specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage 1.2 V Quiescent Current, (per Converter) NFB1 Comparator Trip Point FB2 Comparator Trip Point FB Comparator Hysteresis Not Switching VSHDN = 0V –40°C < TJ < 85°C –40°C < TJ < 125°C –40°C < TJ < 85°C –40°C < TJ < 125°C –1.205 –1.195 1.205 1.195 20 –1.23 1.23 8 30 1 –1.255 1.255 1.255 1.255 μA μA V V V V mV NFB1, FB2 Voltage Line Regulation NFB1 Pin Bias Current (Note 3) FB2 Pin Bias Current (Note 4) Switch Off Time, Switcher 1 (Note 5) 1.2V < VIN < 12V VNFB1= –1.23V –40°C < TJ < 85°C –40°C < TJ < 125°C 0.05 0.1 l 1.3 2 2.9 30 80 300 400 %/V μA nA nA ns Switch Off Time, Switcher 2 (Note 5) Switch VCESAT Switch Current Limit VFB2 > 1V VFB2 < 0.6V ISW = 300mA 400 1.5 250 350 250 350 400 ns μs mV mA 1945fa 2 LT1945 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V u.


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