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LM2941S датащи(PDF) 9 Page - Texas Instruments |
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LM2941S датащи(HTML) 9 Page - Texas Instruments |
9 / 26 page LM2941, LM2941C www.ti.com SNVS770G – JUNE 1999 – REVISED APRIL 2013 ON/OFF The ON/OFF pin has no internal pull-up or pull-down to establish a default condition and, as a result, this pin must be terminated externally, either actively or passively. The ON/OFF pin requires a low level to enable the output, and a high level to disable the output. To ensure reliable operation, the ON/OFF pin voltage must rise above the maximum ON/OFF(OFF) voltage threshold (2.00V) to disable the output, and must fall below the minimum ON/OFF(ON) voltage threshold (0.80V) to enable the output. If the ON/OFF function is not needed this pin can be connected directly to Ground. If the ON/OFF pin is being pulled to a high state through a series resistor, an allowance must be made for the ON/OFF pin current that will cause a voltage drop across the pull-up resistor. Thermal Overload Protection The LM2941 incorporates a linear form of thermal protection that limits the junction temperature (TJ) to typically 155°C. Should the LM2941 see a fault condition that results in excessive power dissipation and the junction temperature approaches 155°C, the device will respond by reducing the output current (which reduces the power dissipation) to hold the junction temperature at 155°C. Thermal Overload protection is not an ensured operating condition. Operating at, or near to, the Thermal Overload condition for any extended period of time is not encouraged, or recommended, as this may shorten the lifetime of the device. Power Dissipation Consideration should be given to the maximum power dissipation (PD(MAX)) which is limited by the maximum operating junction temperature (TJ(MAX)) of 125°C, the maximum operating ambient temperature (TA(MAX)) of the application, and the thermal resistance ( θJA) of the package. Under all possible conditions, the junction temperature (TJ) must be within the range specified in the Operating Ratings. The total power dissipation of the device is given by: PD = ( (VIN − VOUT) x IOUT) + (VIN x IGND) (3) where IGND is the operating ground pin current of the device (specified under Electrical Characteristics). The maximum allowable junction temperature rise ( ΔTJ) depends on the maximum expected ambient temperature (TA(MAX)) of the application, and the maximum allowable junction temperature (TJ(MAX)): ΔTJ = TJ(MAX) − TA(MAX) (4) The maximum allowable value for junction to ambient Thermal Resistance, θJA, required to keep the junction temperature, TJ, from exceeding maximum allowed can be calculated using the formula: θJA = ΔTJ / PD(MAX) (5) The maximum allowable power dissipation, PD(MAX), required allowed for a specific ambient temperature can be calculated using the formula: PD(MAX) = ΔTJ / θJA (6) Additional information for thermal performance of surface mount packages can be found in AN-1520: A Guide to Board Layout for Best Thermal Resistance for Exposed Packages (literature number SNVA183), AN-1187: Leadless Leadframe Package (LLP) (literature number SNOA401), and AN-2020: Thermal Design By Insight, Not Hindsight (literature number SNVA419). TO-263 Mounting The thermal dissipation of the TO-263 package is directly related to the printed circuit board construction and the amount of additional copper area connected to the TAB. The TAB on the bottom of the TO-263 package is connected to the die substrate via a conductive die attach adhesive, and to device pin 3. As such, it is strongly recommend that the TAB area be connected to copper area directly under the TAB that is extended into the ground plane via multiple thermal vias. Alternately, but not recommended, the TAB may be left floating (i.e. no direct electrical connection). The TAB must not be connected to any potential other than ground. Copyright © 1999–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2941 LM2941C |
Аналогичный номер детали - LM2941S |
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Аналогичное описание - LM2941S |
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