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LM5045MHX/NOPB.A Datasheet(PDF) 28 Page - Texas Instruments |
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LM5045MHX/NOPB.A Datasheet(HTML) 28 Page - Texas Instruments |
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28 / 47 page  1.25V 20 2A 0.4V SHUTDOWN OVP 1.25V STANDBY VPWR 5V R1 R2 R3 LM5045 STANDBY UVLO 20 2A OVP LM5045 1.25V 20 2A STANDBY VPWR 5V R1 R2 LM5045 SNVS699H – FEBRUARY 2011 – REVISED JANUARY 2015 www.ti.com Figure 23. Basic OVP Configuration Figure 24. UVLO/OVP Divider The UVLO and OVP can also be set together using a 3 resistor divider ladder as shown in Figure 24. R1 is calculated as explained in the basic UVLO divider selection. Using the same values, as in the above two examples, for the UVLO and OVP set points, R1 and R3 remain the same at 100 kΩ and 1.5 kΩ. The R2 is 2.7 k Ω obtained by subtracting R3 from 4.2 kΩ. Remote configuration of the controller’s operational modes can be accomplished with open drain device(s) connected to the UVLO pin as shown in Figure 25. Figure 26 shows an application of the OVP comparator for Remote Thermal Protection using a thermistor (or multiple thermistors) which may be located near the main heat sources of the power converter. The negative temperature coefficient (NTC) thermistor is nearly logarithmic, and in this example a 100 k Ω thermistor with the β material constant of 4500 Kelvin changes to approximately 2 k Ω at 130ºC. Setting R1 to one-third of this resistance (665 Ω) establishes 130ºC as the desired trip point (for VREF = 5 V). In a temperature band from 20ºC below to 20ºC above the OVP threshold, the voltage divider is nearly linear with 25mV per ºC sensitivity. R2 provides temperature hysteresis by raising the OVP comparator input by R2 x 20µA. For example, if a 22kΩ resistor is selected for R2, then the OVP pin voltage will increase by 22 kΩ x 20 µA = 506 mV. The NTC temperature must therefore fall by 506 mV / 25 mV per ºC = 20ºC before the LM5045 switches from standby mode to the normal mode. 28 Submit Documentation Feedback Copyright © 2011–2015, Texas Instruments Incorporated Product Folder Links: LM5045 |
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