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LTM8022EV-PBF Datasheet(PDF) 11 Page - Linear Technology |
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LTM8022EV-PBF Datasheet(HTML) 11 Page - Linear Technology |
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11 / 20 page  LTM8022 11 8022fb APPLICATIONS INFORMATION Load Sharing Two or more LTM8022’s may be paralleled to produce higher currents. To do this, tie the VIN, VOuT and SHARE pins of all the paralleled LTM8022’s together. Synchronize the LTM8022s to avoid beat frequencies if required. To ensure that paralleled modules start up together, the RUN/SS pins may be tied together, as well. If the RUN/SS pins are not tied together, make sure that the same valued soft-start capacitors are used for each module. An example of two LTM8022 modules configured for load sharing is given in the Typical Applications section. Soft-Start The RUN/SS pin can be used to soft-start the LTM8022, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 2 shows the start-up and shutdown waveforms with the soft-start circuit. By choos- ing an appropriate RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply at least 20μA when the RUN/SS pin reaches 2.5V. Synchronization The internal oscillator of the LTM8022 can be synchronized by applying an external 250kHz to 2MHz clock signal to the SYNC pin. The resistor tied from the RT pin to ground should be chosen such that the LTM8022 would free run 20% lower than the intended synchronization frequency (see Frequency Selection section). When the LTM8022 is synchronized to an external clock source, Burst Mode operation is disabled. The part will skip power switching cycles as necessary to maintain regulation. Ensure that the SYNC pin is not left floating. Tie it to GND if not used. Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8022 is absent. This may occur in battery charging applications, or in battery backup systems where a battery or some other supply is diode ORed with the LTM8022’s output. If the VIN pin is allowed to float, and the RUN/SS pin is held high (either by a logic signal or because it is tied to VIN), then the LTM8022’s internal circuitry will pull its quiescent current through its internal power switch. This is fine if your system can tolerate a few milliamps in this state. If you ground the RUN/SS pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LTM8022 can pull large currents from the output through the VIN pin. Figure 3 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. Figure 2. To Soft-Start the LTM8022, Add a Resistor and Capacitor to the RUN/SS Pin Figure 3. The Input Diode Prevents a Shorted Input from Discharging a Back-Up Battery Tied to the Output. It Also Protects the Circuit From a Reversed Input. The LTM8022 Runs Only When the Input is Present 8022 F02 IL 0.5A/DIV VRUN/SS 2V/DIV VOUT 2V/DIV RUN/SS GND 0.22μF RUN 15k 2ms/DIV LTM8022 8022 F03 VIN VOUT RUN/SS VIN SYNC PG BIAS AUX VOUT RT GND ADJ |
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Similar Description - LTM8022EV-PBF |
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