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LP5907MFX-1.8 Datasheet(PDF) 11 Page - Texas Instruments |
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LP5907MFX-1.8 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 21 page LP5907 www.ti.com SNVS798D – APRIL 2012 – REVISED NOVEMBER 2012 CAPACITOR CHARACTERISTICS The LP5907 is designed to work with ceramic capacitors on the input and output to take advantage of the benefits they offer. For capacitance values in the range of 1 µF to 10 µF, ceramic capacitors are the smallest, least expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a typical 1 µF ceramic capacitor is in the range of 20 m Ω to 40 mΩ, which easily meets the ESR requirement for stability for the LP5907. The temperature performance of ceramic capacitors varies by type and manufacturer. Most large value ceramic capacitors ( ≥2.2 µF) are manufactured with Z5U or Y5V temperature characteristics, which results in the capacitance dropping by more than 50% as the temperature goes from 25°C to 85°C. A better choice for temperature coefficient in a ceramic capacitor is X7R. This type of capacitor is the most stable and holds the capacitance within ±15% over the temperature range. Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 1 µF to 10 µF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the temperature goes from 25°C down to –40°C, so some guard band must be allowed. REMOTE CAPACITOR OPERATION The LP5907 requires at least a 1-µF capacitor at output pin, but there is no strict requirements about the location of the capacitor in regards the LDO output pin. In practical designs the output capacitor may be located some 5- 10 cm away from the LDO. This means that there is no need to have a special capacitor close to the output pin if there is already respective capacitors in the system (like a capacitor at the input of supplied part). The remote capacitor feature helps user to minimize the number of capacitors in the system. As a good design practice, it is good to keep the wiring parasitic inductance at a minimum, which means to use as wide as possible traces from the LDO output to the capacitors, keeping the LDO trace layer as close as possible to ground layer and avoiding vias on the path. If there is a need to use vias, implement as many as possible vias between the connection layers. The recommendation is to keep parasitic wiring inductance less than 35 nH. For the applications with fast load transients, it is recommended to use an input capacitor equal to or larger to the sum of the capacitance at the output node for the best load transient performance. NO-LOAD STABILITY The LP5907 will remain stable and in regulation with no external load. ENABLE CONTROL The LP5907 may be switched ON or OFF by a logic input at the ENABLE pin. A high voltage at this pin will turn the device on. When the enable pin is low, the regulator output is off and the device typically consumes 3 nA. However if the application does not require the shutdown feature, the VEN pin can be tied to VIN to keep the regulator output permanently on. A 1-M Ω pulldown resistor ties the VEN input to ground, this ensures that the device will remain off when the enable pin is left open circuit. To ensure proper operation, the signal source used to drive the VEN input must be able to swing above and below the specified turn-on/off voltage thresholds listed in the Electrical Characteristics section under VIL and VIH. MICRO SMD MOUNTING The micro SMD package requires specific mounting techniques, which are detailed in Texas Instruments Application Note AN-1112. For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the micro SMD device. Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LP5907 |
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