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LT1939 Datasheet(PDF) 6 Page - Linear Technology |
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LT1939 Datasheet(HTML) 6 Page - Linear Technology |
6 / 24 page LT1939 6 1939f TYPICAL PERFORMANCE CHARACTERISTICS Boost Current vs Switch Current Minimum Boost Voltages vs Temperature Minimum Input Voltage LDRV Dropout Voltage vs Temperature Inductor Value for 2A Maximum Load Current (VOUT = 3.3V, IRIPPLE = 250mA) VIN (Pin 1): The VIN pin powers the internal control circuitry and is monitored by an undervoltage comparator. The VIN pin is also connected to the collectors of the internal power NPN switch and linear output NPN. The VIN pin has high dI/dt edges and must be decoupled to ground close to the pin of the device. SHDN (Pin 2): The SHDN pin is used to shut down the LT1939 and reduce quiescent current to a typical value of 12μA. The accurate 0.76V threshold and input current hysteresis can be used as an undervoltage lockout, prevent- ing the regulator from operating until the input voltage has reached a predetermined level. Force the SHDN pin above its threshold or let it float for normal operation. SS (Pin 3): The SS pin is used to control the slew rate of the output of both the switching and linear regulators. A single capacitor from the SS pin to ground determines the regulators’ ramp rate. For soft-start details see the Applications Information section. Switcher Dropout Operation SWITCH CURRENT (A) 0 30 40 50 1.6 1939 G19 20 10 25 35 45 15 5 0 0.4 0.2 0.8 0.6 1.2 1.4 1.8 1.0 2.0 150°C 25°C –50°C TEMPERATURE (°C) –50 1.5 1.7 1.9 2.1 2.3 050 100 150 1939 G20 2.5 2.7 –25 25 75 125 MINIMUM BOOST FOR SWITCH SATURATION LOAD CURRENT (A) 0 8 7 6 5 4 3 2 1 0 1.6 1939 G21 0.4 0.8 1.2 2.0 1.4 0.2 0.6 1.0 1.8 VOUT1 = 5V VOUT1 = 3.3V FSW = 1MHz L = 3.3μH TEMPERATURE (°C) –50 1.00 1.05 1.15 1.20 1.25 1.50 1.35 0 50 75 1939 G22 1.10 1.40 1.45 1.30 –25 25 100 125 150 ILDRV = 5mA INPUT VOLTAGE (V) 2.5 0 1 2 3 4 6 3.0 3.5 4.0 4.5 1939 G23 5.0 5.5 5 IOUT1 = 1A VOUT1 = 5V VOUT1 = 3.3V INPUT VOLTAGE (V) 5 250 500 1000 1250 1500 2500 1939 G24 750 15 10 20 25 1750 2000 2250 L = 3.3μH L = 4.7μH L = 6.8μH L = 10μH L = 1.5μH L = 2.2μH L = 1μH PIN FUNCTIONS |
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