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TS2938 数据表(PDF) 4 Page - Taiwan Semiconductor Company, Ltd |
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TS2938 数据表(HTML) 4 Page - Taiwan Semiconductor Company, Ltd |
4 / 6 page TS2938 500mA Ultra Low Dropout Voltage Regulator with Inhibit Function 4/6 Version: D07 Application Information (Continue) Output Capacitor The TS2938 series requires an output capacitor to maintain stability and improve transient response. Proper capacitor selection is important to ensure proper operation. The output capacitor selection is dependent upon the ESR of the output capacitor the maintain stability. When the output capacitor is 6.8uF or greater, the output capacitor should have an ESR less than 2 ohm. This will improve transient response as well as promoted stability. Ultra low ESR capacitors (<100mohm), such as ceramic chip capacitors may promote instability. These very low ESR levels may cause an oscillation and/or under damped transient response. A low ESR solid tantalum capacitor works extremely well and provide good transient response and stability over temperature. Aluminum electrolytic can also be used, as long as the ESR of the capacitor is <2ohm. The value of the output capacitor can be increased without limit. Higher capacitance values help to improved transient response and ripple rejection and reduce output noise. Minimum Load Current The TS2938 series is specified between finite loads. If the output current is too small leakage currents dominate and the output voltage rises. A 5mA minimum load current is necessary for proper regulation. Input Capacitor An input capacitor of 1uF or greater is recommended when the device is more that 4 inches away from the bulk AC supply capacitance or when the supply is a battery. Small and surface mount ceramic chip capacitors can be used for bypassing. Larger values will help to improve ripple rejection by bypassing the input to the regulator, further improving the integrity of the output voltage. Thermal Characteristics A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the application. Under all possible operating conditions, the junction temperature must be within the range specified under absolute maximum ratings. To determine if the heatsink is required, the power dissipated by the regulator, PD must be calculated. The below formula shows the voltages and currents for calculating the PD in the regulator: IIN = IL / IG PD = (VIN-VOUT) * IL + (VIN) * IG Ex. PD = (3.3V-2.5V) * 0.5A + 3.3V * 11mA = 400mW + 36mW = 436mW The next parameter which must be calculated the maximum allowable temperature rise. TR(max) is calculated by the using to formula: TR(max) = TJ(max) – TA(max) Where: TJ(max) is the maximum allowable junction temperature, which is 125 oC for commercial grade parts. TA(max) is the maximum ambient temperature which will be encountered in the application. Using the calculated values for TA(max) and PD, the maximum allowable value for the junction to ambient thermal resistance, θJA, can now be found: θJA = TR(max) / PD Inhibit Input TS2938 feature an active-low (Inhibit) input that allows ON/OFF control of the regulator. The Inhibit input has TTL/CMOS compatible thresholds for simple interfacing with logic interfacing. Inhibit should be directly tied to Ground or keep open (not connected). |
类似零件编号 - TS2938_08 |
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类似说明 - TS2938_08 |
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