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LP38691QSD-1.8 Datasheet(PDF) 11 Page - Texas Instruments |
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LP38691QSD-1.8 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 27 page LP38691, LP38693 www.ti.com SNVS321K – JANUARY 2005 – REVISED APRIL 2013 APPLICATION HINTS EXTERNAL CAPACITORS Like any low-dropout regulator, external capacitors are required to assure stability. These capacitors must be correctly selected for proper performance. INPUT CAPACITOR: An input capacitor of at least 1µF is required (ceramic recommended). The capacitor must be located not more than one centimeter from the input pin and returned to a clean analog ground. OUTPUT CAPACITOR: An output capacitor is required for loop stability. It must be located less than 1 centimeter from the device and connected directly to the output and ground pins using traces which have no other currents flowing through them. The minimum amount of output capacitance that can be used for stable operation is 1µF. Ceramic capacitors are recommended (the LP38691/3 was designed for use with ultra low ESR capacitors). The LP38691/3 is stable with any output capacitor ESR between zero and 100 Ohms. ENABLE PIN (LP38693 only): The LP38693 has an Enable pin (EN) which allows an external control signal to turn the regulator output On and Off. The Enable On/Off threshold has no hysteresis. The voltage signal must rise and fall cleanly, and promptly, through the ON and OFF voltage thresholds. The Enable pin has no internal pull-up or pull-down to establish a default condition and, as a result, this pin must be terminated either actively or passively. If the Enable pin is driven from a source that actively pulls high and low, the drive voltage should not be allowed to go below ground potential or higher than VIN. If the application does not require the Enable function, the pin should be connected directly to the VIN pin. Foldback Current Limiting: Foldback current limiting is built into the LP38691/3 which reduces the amount of output current the part can deliver as the output voltage is reduced. The amount of load current is dependent on the differential voltage between VIN and VOUT. Typically, when this differential voltage exceeds 5V, the load current will limit at about 350 mA. When the VIN - VOUT differential is reduced below 4V, load current is limited to about 850 mA. SELECTING A CAPACITOR It is important to note that capacitance tolerance and variation with temperature must be taken into consideration when selecting a capacitor so that the minimum required amount of capacitance is provided over the full operating temperature range. Capacitor Characteristics CERAMIC For values of capacitance in the 10 to 100 µF range, ceramics are usually larger and more costly than tantalums but give superior AC performance for bypassing high frequency noise because of very low ESR (typically less than 10 m Ω). However, some dielectric types do not have good capacitance characteristics as a function of voltage and temperature. Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V also exhibit a severe temperature effect, losing more than 50% of nominal capacitance at high and low limits of the temperature range. X7R and X5R dielectric ceramic capacitors are strongly recommended if ceramics are used, as they typically maintain a capacitance range within ±20% of nominal over full operating ratings of temperature and voltage. Of course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance. Copyright © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LP38691 LP38693 |
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Similar Description - LP38691QSD-1.8 |
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