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LTC1751-5 Datasheet(PDF) 9 Page - Linear Technology |
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LTC1751-5 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  LTC3245 9 3245f For more information www.linear.com/LTC3245 applicaTions inForMaTion Short-Circuit/Thermal Protection The LTC3245 has built-in short-circuit current limiting as well as overtemperature protection. During short-circuit conditions the device will automatically limit the output current. The LTC3245 has thermal protection that will shut down the device if the junction temperature exceeds the overtemperature threshold (typically 175°C). Thermal shutdown is included to protect the IC in cases of exces- sively high ambient temperatures, or in cases of excessive power dissipation inside the IC. The charge transfer will reactivate once the junction temperature drops back to approximately 165°C. When the thermal protection is active, the junction tem- perature is beyond the specified operating range. Thermal protection is intended for momentary overload conditions outsidenormaloperation.Continuousoperationabovethe specified maximum operating junction temperature may impair device reliability. Soft-Start Operation To prevent excessive current flow at VIN during start-up, the LTC3245 has built-in soft-start circuitry. Soft-start is achieved by increasing the amount of current available to the output charge storage capacitor linearly over a period of approximately 500μs. Soft-start is enabled whenever the device is brought out of shutdown, and is disabled shortly after regulation is achieved. Programming the Output Voltage (OUTS/ADJ Pin) The LTC3245 output voltage programming is very flexible offering a fixed 3.3V output, fixed 5V output as well as adjustable output that is programmed through an external resistor divider. The desired output regulation method is selected through the SET pins. For a fixed output simply short OUTS (OUTS/ADJ pin) to VOUT as shown in Figure 1. Fixed 3.3V operation is enabled by driving both SEL1 and SEL2 pins high, while fixed 5V operating is selected by driving SEL2 high with SEL1 low. Driving both SEL1 and SEL2 low shuts down the device causing VOUT to go high impedance. Figure 1: Fixed Output Operation Figure 2: Adjustable Output Operation Adjustable output programming is accomplished by con- necting ADJ (OUTS/ADJ pin) to a resistor divider between VOUT and GND as shown in Figure 2. Adjustable operation is enabled by driving SEL1 high and SEL2 low. Driving both SEL1 and SEL2 low shuts down the device causing VOUT to go high impedance. VOUT OUTS GND LTC3245 VOUT FIXED 3.3V OR FIXED 5V 3245 F01 COUT VOUT ADJ GND LTC3245 VOUT 3245 F02 COUT RA RB 1.2V ( ) 1+ RA RB Using adjustable operation the output (VOUT) can be programmed to regulate from 2.5V to 5V. The limited programming range provides the required VOUT operating voltage without overstressing the VOUT pin. The desired adjustable output voltage is programmed by solving the following equation for RA and RB: RA RB = VOUT 1.2V –1 Select a value for RB in the range of 1k to 1M and solve for RA. Note that the resistor divider current adds to the total no load operating current. Thus a larger value for RB will result in lower operating current. |
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Similar Description - LTC1751-5 |
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