Document
LT1912 36V, 2A, 500kHz Step-Down Switching Regulator FEATURES
Wide Input Range: Operation From 3.6V to 36V ■ 2A Maximum Output Current ■ Adjustable Switching Frequency: 200kHz to 500kHz ■ Low Shutdown Current: I < 1μA Q www.DataSheet4U.com ■ Integrated Boost Diode ■ Synchronizable Between 250kHz to 500kHz ■ Saturating Switch Design: 0.25Ω On-Resistance ■ 0.790V Feedback Reference Voltage ■ Output Voltage: 0.79V to 20V ■ Soft-Start Capability ■ Small 10-Pin Thermally Enhanced MSOP and (3mm × 3mm) DFN Packages
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DESCRIPTION
The LT®1912 is an adjustable frequency (200kHz to 500kHz) monolithic step-down switching regulator that accepts input voltages up to 36V. A high efficiency 0.25Ω switch is included on the die along with a boost Schottky diode and the necessary oscillator, control, and logic circuitry. Current mode topology is used for fast transient response and good loop stability. The LT1912 allows the use of ceramic capacitors resulting in low output ripple while keeping total solution size to a minimum. The low current shutdown mode reduces input supply current to less than 1μA while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). The LT1912 is available in 10-Pin MSOP and 3mm × 3mm DFN packages with exposed pads for low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIONS
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Automotive Battery Regulation Set Top Box Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
VIN 4.5V TO 36V VIN OFF ON 20k 4.7μF 470pF 68.1k VC RT 316k GND FB 100k 47μF 50 0
1912 TA01
Efficiency
VOUT 3.3V 2A 100 VOUT = 5V 90 EFFICIENCY (%) VOUT = 3.3V
BD BOOST 0.47μF LT1912 SW 6.8μH
RUN/SS
80
70
60 VIN = 12V L = 6.8μF F = 500kHz 0.5 1.0 1.5 LOAD CURRENT (A) 2
1912 TA01b
SYNC
1912f
1
LT1912 ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, RUN/SS Voltage .................................................36V BOOST Pin Voltage ...................................................56V BOOST Pin Above SW Pin.........................................30V FB, RT, VC Voltage .......................................................5V BD, SYNC Voltage .....................................................30V
Operating Junction Temperature Range (Note 2) LT1912E ........................................... –40°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only) ........................................................... 300°C
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PIN CONFIGURATION
TOP VIEW BD BOOST SW VIN RUN/SS 1 2 3 4 5 11 10 RT 9 VC 8 FB 7 N/C 6 SYNC TOP VIEW BD BOOST SW VIN RUN/SS 1 2 3 4 5 10 9 8 7 6 RT VC FB N/C SYNC
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DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN JA = 45°C/W, JC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE 10-LEAD PLASTIC MSOP JA = 45°C/W, JC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT1912EDD#PBF LT1912EMSE#PBF TAPE AND REEL LT1912EDD#TRPBF LT1912EMSE#TRPBF PART MARKING LDJT LTDJS PACKAGE DESCRIPTION 10-Lead (3mm × 3mm) Plastic DFN 10-Lead Plastic MSOP TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. 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
PARAMETER Minimum Input Voltage Quiescent Current from VIN
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2)
CONDITIONS
●
MIN
TYP 3 0.01 450 1.3 0.01 0.9 1 2.7
MAX 3.6 0.5 600 1.7 0.5 1.3 5 3
UNITS V μA μA μA μA mA μA V
VRUN/SS = 0.2V VBD = 3V, Not Switching VBD = 0, Not Switching VRUN/SS = 0.2V VBD = 3V, Not Switching VBD = 0, Not Switching
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Quiescent Current from BD
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Minimum Bias Voltage (BD Pin)
1912f
2
LT1912 ELECTRICAL CHARACTERISTICS
PARAMETER Feedback Voltage
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The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V VBOOST = 15V, VBD = 3.3V unless otherwise noted. (Note 2)
CONDITIONS MIN 780 775 TYP 790 790 7 0.002 25 1000 45 45 3.5 2 RT = 187k
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MAX 800 805 30 0.01
UNITS mV mV nA %/V μMho μA μA A/V V
FB Pin Bias Current (Note 3) FB Voltage Line Regulation Error Amp gm Error Amp Gain
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C
VFB = 0.8V, VC = 0.4V 4V < VIN < 36V
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VC Sink Current VC Pin to Switch Current Gain VC Clamp Voltage Switching Frequency Minimum Switch Off-Time Switch Current Limit Switch VCE.