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LTC3535 Datasheet(PDF) 9 Page - Linear Technology |
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LTC3535 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  LTC3535 9 3535fa OPERATION The LTC3535 is a dual channel 1MHz synchronous boost converter housed in a 12-lead 3mm × 3mm DFN package. Each channel is identical and fully independent. They can operate from the same source, or from different voltage sources. In addition, their output voltages can be tied together to allow operation of a single output from two different input sources. However, note that the two channels are not designed to current share, so if both input voltages are present either one may be supplying the load. The following description of operation applies to each channel. Note that references to VIN or VOUT apply to the corresponding channel. With a guaranteed ability to start up and operate from inputs less than 0.8V, each channel features fixed fre- quency, current mode PWM control for exceptional line and load regulation. The current mode architecture with adaptive slope compensation provides excellent transient load response, requiring minimal output filtering. Internal soft-start and internal loop compensation simplifies the design process while minimizing the number of external components. WithitslowRDS(ON)andlowgatechargeinternalN-channel MOSFET switch and P-channel MOSFET synchronous rectifier, the LTC3535 achieves high efficiency over a wide range of load currents. Burst Mode operation maintains high efficiency at very light loads, reducing the quiescent current to just 9µA per channel. Operation can be best understood by referring to the Block Diagram. LOW VOLTAGE START-UP The LTC3535 includes an independent start-up oscillator designed to start up at an input voltage of 0.68V (typical). Soft-start and inrush current limiting are provided during start-up, as well as normal mode. When either VIN or VOUT for a given channel exceeds 1.3V typical, the channel enters normal operating mode. When the output voltage exceeds the input by 0.24V, the channel powers itself from VOUT instead of VIN. At this point the internal circuitry has no dependency on the VIN input volt- age,eliminatingtherequirementforalargeinputcapacitor. The input voltage can drop as low as 0.5V. The limiting factor for the application becomes the availability of the power source to supply sufficient energy to the output at lowvoltages,andmaximumdutycycle,whichisclampedat 90% typical. Note that at low input voltages, small voltage drops due to series resistance become critical, and greatly limit the power delivery capability of the converter. LOW NOISE FIXED FREQUENCY OPERATION Soft-Start The LTC3535 contains internal circuitry to provide soft- start operation. The soft-start circuitry slowly ramps the peak inductor current from zero to its peak value of 750mA (typical) in approximately 0.5ms, allowing start-up into heavy loads. The soft-start circuitry is reset in the event of a shutdown command or a thermal shutdown. Oscillator An internal oscillator (independent for each channel) sets the switching frequency to 1MHz. Shutdown Shutdown is accomplished by pulling the SHDN pin below 0.3V and enabled by pulling the SHDN pin above 0.8V. Although SHDN can be driven above VIN or VOUT (up to the absolute maximum rating) without damage, the LTC3535 has a proprietary test mode that may be engaged if SHDN is held in the range of 0.5V to 1V higher than the greater of VIN or VOUT. If the test mode is engaged, normal PWM switching action is interrupted, which can cause undesir- able operation in some applications. Therefore, in appli- cations where SHDN may be driven above VIN, a resistor dividerorothermeansmustbeemployedtokeepthe SHDN voltage below (VIN + 0.4V) to prevent the possibility of (Refer to Block Diagram) |
Similar Part No. - LTC3535_15 |
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Similar Description - LTC3535_15 |
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