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LT1107 Datasheet(PDF) 10 Page - Linear Technology |
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LT1107 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  10 LT1107 1107fa VOUTshould be less than 6.2V. More negative output voltages can be accommodated as in the prior section. In Figure 4, the input is negative while the output is positive. In this configuration, the magnitude of the input voltage can be higher or lower than the output voltage. A level shift, provided by the PNP transistor, supplies proper polarity feedback information to the regulator. Figure 4. Negative-to-Positive Converter Using the ILIM Pin The LT1107 switch can be programmed to turn off at a set switch current, a feature not found on competing devices. This enables the input to vary over a wide range without exceeding the maximum switch rating or saturating the inductor. Consider the case where analysis shows the LT1107 must operate at an 800mA peak switch current with a 2V input. If VIN rises to 4V, the peak switch current will rise to 1.6A, exceeding the maximum switch current rating. With the proper resistor selected (see the “Maxi- mum Switch Current vs RLIM” characteristic), the switch current will be limited to 800mA, even if the input voltage increases. Another situation where the ILIM feature is useful occurs when the device goes into continuous mode operation. This occurs in step-up mode when: V V VV DC OUT DIODE IN SW + − < − 1 1 24 () When the input and output voltages satisfy this relation- ship, inductor current does not go to zero during the switch OFF time. When the switch turns on again, the current ramp starts from the non-zero current level in the inductor just prior to switch turn-on. As shown in Figure 5, the inductor current increases to a high level before the comparator turns off the oscillator. This high current can cause excessive output ripple and requires oversizing the output capacitor and inductor. With the ILIM feature, the switch turns off at the programmed current as shown in Figure 6, keeping output ripple to a minimum. D1 L1 ILIM VIN FB SW2 GND C1 LT1107 1107 F04 +VOUT –VIN R2 SW1 C2 2N3906 R1 VOUT = 1.25V + 0.6V ()R1 R2 R3 + + D1 1N5818 L1 R3 ILIM VIN FB SW2 GND C1 LT1107 1107 F03 +VIN –VOUT R1 R2 SW1 C2 + + Figure 3. Positive-to-Negative Converter S APPLICATI I FOR ATIO |
Similar Part No. - LT1107_15 |
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Similar Description - LT1107_15 |
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