lt1339 Linear Technology Corporation, lt1339 Datasheet
lt1339
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lt1339 Summary of contents
Page 1
... The IC also incor- porates user-adjustable slope compensation for minimi- zation of magnetics at duty cycles up to 90%. The LT1339 timing oscillator operating frequency is pro- grammable and can be synchronized up to 150kHz. Mini- mum off-time operation provides main switch protection. The IC also incorporates a soft start feature that is gated by both shutdown and undervoltage lockout conditions ...
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... RUN/SHDN Pin Voltage ...................... – 0.3V to 12V All Other Inputs .......................................– 0. Maximum Currents 5V Reference Output Current............................ 65mA Maximum Temperatures Operating Ambient Temperature Range LT1339C ............................................ LT1339I ......................................... – Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL C HARA TERISTICS C 12V ...
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... Note 2: Supply current specification does not include external FET gate charge currents. Actual supply currents will be higher and vary with operating frequency, operating voltages and the type of external FETs used. See Application Information section. Note 3: Test condition: R Note 4: Test Condition: V LT1339 = 25 C unless otherwise noted. A MIN TYP MAX 1 ...
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... LT1339 W U TYPICAL PERFORMANCE CHARACTERISTICS Boost Supply Current vs Temperature 4.0 3.5 3.0 2.5 2.0 1.5 1.0 50 100 125 –50 – TEMPERATURE ( C) 1339 G01 I Shutdown Current vs 12VIN Temperature 190 180 170 160 150 140 130 –50 – 100 125 TEMPERATURE ( C) 1339 G04 Error Amplifier Voltage Gain vs Temperature 4 ...
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... TOP GATE CAPACITANCE (pF) 1339 G14 Boost Supply Current vs 12V 1339 G16 LT1339 RUN/SHDN Threshold Hysteresis vs Temperature 125 –50 – TEMPERATURE ( C) Average Current Limit Threshold Sense Voltage Tolerance vs Common Mode Voltage ...
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... LT1339 W U TYPICAL PERFORMANCE CHARACTERISTICS UVLO Thresholds vs Temperature 10.00 9.75 RISING 9.50 9.25 9.00 FALLING 8.75 8.50 8.25 8.00 – –50 100 TEMPERATURE ( C) 1339 G18 RUN/SHDN Input Current vs Pin Voltage 800 FULL OPERATING 700 TEMPERATURE RANGE 600 500 UPPER LIMIT 400 300 200 100 0 0 0.5 1.0 (1.25) RUN/SHDN INPUT VOLTAGE (V) ...
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... FET and inductive switch node. TG (Pin 19): Topside (Boost) Output Driver. Connects to gate of topside external power FET. V (Pin 20): Topside Power Supply. Bootstrapped BOOST via 1 F capacitor tied to switch node (Pin 18) and Schottky diode connected to the 12V LT1339 (typically through IN decoupling IN supply. IN sn1339 1339fas 7 ...
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... U OPERATION (Refer to Functional Block Diagram) Basic Control Loop The LT1339 uses a constant frequency, current mode synchronous architecture. The timing of the IC is provided through an internal oscillator circuit, which can be syn- chronized to an external clock, programmable to operate at frequencies up to 150kHz. The oscillator creates a modified sawtooth wave at its timing node (CT) with a slow charge, rapid discharge characteristic ...
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... FB Shutdown The LT1339 can be put into low current shutdown mode by pulling the RUN/SHDN pin low, disabling all circuit functions. The shutdown threshold is a bandgap referred voltage of 1.25V typical. Use of a precision threshold on C ...
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... APPLICATIONS INFORMATION R Selection for Output Current SENSE R generates a voltage that is proportional to the SENSE inductor current for use by the LT1339 current sense amplifier. The value based on the required SENSE load current. The average current limit function has a typical threshold of 120mV/R SENSE R ...
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... LT1339 regu- lator from drawing large currents until the input supply is able to provide the required power. If additional hysteresis is desired for the enable function, an external feedback resistor can be used from the LT1339 , to full average regulator output. If connection to the regulator output is BE ...
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... MOSFET gates, preventing parasitic turn-on and damage to the MOSFETs. Inductor Selection The inductor for an LT1339 converter is selected based on output power, operating frequency and efficiency require- ments. Generally, the selection of inductor value can be reduced to desired maximum ripple current in the inductor ( I) ...
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... The LT1339, however, uses a current limit scheme that is independent of slope compensation effects (average current limit). This provides operation at any duty ...
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... Once voltage requirements have been determined, R can be selected based on allowable power dissipation and required output current LT1339 buck converter, the average inductor current is equal to the DC load current. The average currents through the main and synchronous switches are: I ...
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... In some applications, parasitic FET capacitances couple the negative going switch node transient onto the bottom gate drive pin of the LT1339, causing a negative voltage in excess of the Absolute Maximum Rating to be imposed on that pin. Connection of a catch Schottky (rated to about 1A is typically sufficient) from this pin to ground will eliminate this effect ...
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... C and thus, the associated transition losses. RSS Gate Drive Buffers The LT1339 is designed to drive relatively large capacitive loads. However, in certain applications, efficiency im- provements can be realized by adding an external buffer stage to drive the gates of the FET switches. When the switch gates load the driver outputs such that rise/fall times exceed about 100ns, buffers can sometimes result in efficiency gains ...
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... U TYPICAL APPLICATIONS LT1339 sn1339 1339fas 17 ...
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... LT1339 U TYPICAL APPLICATIONS 18 RTOP RMID COMP GND-S V GND PGND SGND REF V MURS120 SENSE AVG – I SL/ADJ SENSE + CT TS REF 5V TG SYNC BOOST V EFFICIENCY sn1339 1339fas ...
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... SW Package 20-Lead Plastic Small Outline (Wide 0.300) (LTC DWG # 05-08-1620) 0.037 – 0.045 (0.940 – 1.143) 0.050 (1.270) TYP 0.004 – 0.012 0.014 – 0.019 (0.102 – 0.305) (0.356 – 0.482) TYP LT1339 V OUT 28V C + OUT 2200 F 35V 6 IRF3205 2 D1 IR30BQ060 ...
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... L1 = Kool M , 12T 4X12 ON 77439-A7 Kool REGISTERED TRADEMARK OF MAGNETICS, INC. 48V to 5V Efficiency 100 OUTPUT CURRENT (AMPS) LT1339 • TA02 V IN 48V + C IN 1500 F Q1 63V, 6 IRFZ44 MMSZ4684 IRFZ44 4 ...