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LSM-1.8 Datasheet(PDF) 6 Page - Murata Manufacturing Co., Ltd. |
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LSM-1.8 Datasheet(HTML) 6 Page - Murata Manufacturing Co., Ltd. |
6 / 13 page The highest temperatures in LSM D3 SMT's occur at their output inductor, whose heat is generated primarily by I2R losses. The derating curves were developed using thermocouples to monitor the inductor temperature and varying the load to keep that temperature below +110°C under the assorted conditions of air flow and air temperature. Once the temperature exceeds +115°C (approx.), the thermal protection will disable the converter. Automatic restart occurs after the temperature has dropped below +110°C. As you may deduce from the derating curves and observe in the efficiency curves on the following pages, LSM D3 SMT's are more efficient at lower current levels. Also I2R losses in the output inductor are significantly less at lower current levels. Consequently, LSN-D3 SMT's deliver very impressive temperature performance if operating at less than full load. Lastly, when LSM D3 SMT's are installed in system boards, they are obvi- ously subject to numerous factors and tolerances not taken into account here. If you are attempting to extract the most current out of these units under demanding temperature conditions, we advise you to monitor the output- inductor temperature to ensure it remains below +110°C at all times. Output Reverse Conduction Many DC/DC's using synchronous rectification suffer from Output Reverse Conduction. If those devices have a voltage applied across their output before a voltage is applied to their input (this typically occurs when another power supply starts before them in a power-sequenced application), they will either fail to start or self destruct. In both cases, the cause is the "freewheeling" or "catch" FET biasing itself on and effectively becoming a short circuit. LSM D3 SMT DC/DC converters do not suffer from Output Reverse Conduc- tion. They employ proprietary gate drive circuitry that makes them immune to applied output voltages. Thermal Considerations and Thermal Protection The typical output-current thermal-derating curves shown below enable designers to determine how much current they can reliably derive from each model of the LSM D3 SMT's under known ambient-temperature and air-flow conditions. Similarly, the curves indicate how much air flow is required to reliably deliver a specific output current at known temperatures. Figure 7. Trim Connections Using Fixed Resistors Figure 6. Trim Connections Using a Trimpot Trim Equations Note: Resistor values are in k . Accuracy of adjustment is subject to tolerances of resistors and factory-adjusted, initial output accuracy. VO = desired output voltage. VO NOM = nominal output voltage. Note: LSM-0.8/10-D3 is not trimmable. UP VO – 1 RT (k ) = 1.296 DOWN 1 – VO RT (k ) = – 1 – 1 1.62(VO – 0.8) UP VO – 1.2 RT (k ) = 1.992 DOWN 1.2 – VO RT (k ) = – 2.37 – 2.37 2.49(VO – 0.8) UP VO – VO NOM RT (k ) = 1.896 DOWN VO NOM – VO RT (k ) = – 4.99 – 4.99 2.37(VO – 0.8) LSM-1/10-D3 Model LSM-1.2/10-D3 LSM-1.5/10-D3 LSM-1.8/10-D3 LSM-2/10-D3 LSM-2.5/10-D3 Trim Equations Note: Install either a fixed trim-up resistor or a fixed trim-down resistor depending upon desired output voltage. LSM-10A D3 Models Single Output, Non-Isolated, 3.3VIN, 0.8-2.5VOUT 10 Amp DC/DC’s in SMT Packages Technical enquiries email: sales@murata-ps.com, tel: +1 508 339 3000 www.murata-ps.com MDC_LSM-10A D3.B01 Page 6 of 13 |
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