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LT1073 Datasheet(PDF) 9 Page - Linear Technology |
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LT1073 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LT1073 9 APPLICATIO S I FOR ATIO V R R mV OUT =+ () 1 2 1 212 Step-Down (Buck Mode) Operation A step-down DC/DC converter converts a higher voltage to a lower voltage. It is short-circuit protected because the switch is in series with the output. Step-down converters are characterized by low output voltage ripple but high input current ripple. The usual hookup for an LT1073- based step-down converter is shown in Figure 7. When the switch turns on, SW2 pulls up to VIN – VSW. This puts a voltage across L1 equal to VIN – VSW – VOUT, causing a current to build up in L1. At the end of the switch ON time, the current in L1 is equal to i VV V L t PEAK IN SW OUT ON = –– When the switch turns off the SW2 pin falls rapidly and actually goes below ground. D1 turns on when SW2 reaches 0.4V below ground. D1 MUST BE A SCHOTTKY DIODE. The voltage at SW2 must never be allowed to go below –0.5V. A silicon diode such as the 1N4933 will allow SW2 to go to –0.8V, causing potentially destructive power dissipation inside the LT1073. Output voltage is deter- mined by V R R mV OUT =+ () 1 2 1 212 R3 programs switch current limit. This is especially im- portant in applications where the input varies over a wide range. Without R3, the switch stays on for a fixed time each cycle. Under certain conditions the current in L1 can build up to excessive levels, exceeding the switch rating and/or saturating the inductor. The 220 Ω resistor pro- grams the switch to turn off when the current reaches approximately 400mA. When using the LT1073 in step- down mode, output voltage should be limited to 6.2V or less. Inverting Configurations The LT1073 can be configured as a positive-to-negative converter (Figure 8), or a negative-to-positive converter (Figure 9). In Figure 8, the arrangement is very similar to a step-down, except that the high side of the feedback is referred to ground. This level shifts the output negative. As in the step-down mode, D1 must be a Schottky diode, and VOUTshould be less than 6.2V. Figure 7. Step-Down Mode Hookup VIN + R3 220 Ω L1 D1 1N5818 VOUT C1 + C2 R2 R1 1073 FO7 LT1073 ILIM VIN SW1 SW2 FB GND Figure 8. Positive-to-Negative Converter Figure 9. Negative-to-Positive Converter +VIN + R3 L1 D1 1N5818 –VOUT C1 + C2 R1 R2 1073 FO8 LT1073 ILIM VIN SW1 SW2 FB GND –VIN + L1 D1 +VOUT VOUT = ( )212mV + 0.6V R1 C1 + C2 R2 1073 F09 LT1073 ILIM VIN SW1 FB AO SW2 GND 2N3906 R1 R2 |
Similar Part No. - LT1073_15 |
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Similar Description - LT1073_15 |
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