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LTC3113 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3113 Datasheet(HTML) 10 Page - Linear Technology |
10 / 24 page LTC3113 10 3113f OPERATION Internal Soft-Start The LTC3113 buck-boost converter has an independent internal soft-start circuit with a nominal duration of 2ms. The converter remains in regulation during soft-start and will therefore respond to output load transients which occur during this time. In addition, the output voltage rise time has minimal dependency on the size of the output capaci- tor or load current during start-up. During soft-start, the buck-boost is forced into PWM mode operation regardless of the state of the BURST pin. Thermal Shutdown If the die temperature exceeds 155°C the LTC3113 buck- boost converter will be disabled. All power devices are turned off and the switch nodes will be forced into a high impedance state. The soft-start circuit for the converter is reset during thermal shutdown to provide a smooth recovery once the overtemperature condition is eliminated. When the die temperature drops to approximately 145°C the LTC3113 will restart. For recommendations regarding thermal design of the LTC3113 PCB, refer to the PCB Ther- mal Considerations section in Applications Information. Undervoltage Lockout If the supply voltage decreases below 1.6V (typical) then the LTC3113 buck-boost converter will be disabled and all power devices are turned off. The soft-start circuit is reset during undervoltage lockout to provide a smooth restart once the input voltage rises above 1.7V (typical) the undervoltage lockout increasing threshold. When operating the LTC3113 at low input voltages, care must be taken under heavy loads to prevent the part from cycling into and out of UVLO. When operating at low input voltages the voltage drop created by the source resistance can trigger the UVLO, resetting the part. Operation near the undervoltage lockout is not recommended, but if require- ments dictate, the source resistance should be less than 100mV/IIN(MAX) (where IIN(MAX) is the maximum input current) to ensure proper operation. Inductor Damping When the LTC3113 is in burst operation and sleep mode, active circuits “damp” the inductor voltage through 165Ω (typical) impedance from both SW1 and SW2 to ground minimizing EMI. PWM Mode Operation When the BURST pin is held low, the LTC3113 buck- boost converter operates in a fixed-frequency pulse width modulation (PWM) mode using voltage mode control. Full output current is only available in PWM mode. A proprietary switching algorithm allows the converter to transition between buck, buck-boost, and boost modes without discontinuity in inductor current. The switch topology for the buck-boost converter is shown in Figure 1. Figure 1. Buck-Boost Switch Topology A B D C 3113 F01 L VIN VOUT When the input voltage is significantly greater than the output voltage, the buck-boost converter operates in buck mode. Switch D turns on continuously and switch C remains off. Switches A and B are pulse width modu- lated to produce the required duty cycle to support the output regulation voltage. As the input voltage decreases, switch A remains on for a larger portion of the switching cycle. When the duty cycle reaches approximately 85%, the switch pair AC begins turning on for a small fraction of the switching period. As the input voltage decreases further, the AC switch pair remains on for longer durations and the duration of the BD phase decreases proportionally. As the input voltage drops below the output voltage, the |
Similar Part No. - LTC3113_15 |
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Similar Description - LTC3113_15 |
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