LP5907 datasheet(16/47 Pages) TI

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LP5907

SNVS798O – APRIL 2012 – REVISED JUNE 2020

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The input capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean

analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

NOTE

To ensure stable operation it is essential that good PCB practices are employed to

minimize ground impedance and keep input inductance low. If these conditions cannot be

met, or if long leads are to be used to connect the battery or other power source to the

LP5907, TI recommends increasing the input capacitor to at least 10 µF. Also, tantalum

capacitors can suffer catastrophic failures due to surge current when connected to a low-

impedance source of power (like a battery or a very large capacitor). If a tantalum

capacitor is used at the input, it should be verified by the manufacturer to have a surge

current rating sufficient for the application. The initial tolerance, applied voltage de-rating,

and temperature coefficient must all be considered when selecting the input capacitor to

ensure the actual capacitance is never less than 0.7 µF over the entire operating range.

8.2.2.5 Output Capacitor

The LP5907 is designed specifically to work with a very small ceramic output capacitor, typically 1 µF. A ceramic

capacitor (dielectric types X5R or X7R) in the 1 µF to 10 µF range, and with ESR between 5 mΩ to 500 mΩ, is

suitable in the LP5907 application circuit. For this device the output capacitor should be connected between the

OUT pin and a good connection back to the GND pin.

It may also be possible to use tantalum or film capacitors at the device output, VOUT, but these are not as

attractive for reasons of size and cost (see Capacitor Characteristics).

The output capacitor must meet the requirement for the minimum value of capacitance and have an ESR value

that is within the range 5 mΩ to 500 mΩ for stability. Like the input capacitor, the initial tolerance, applied voltage

de-rating, and temperature coefficient must all be considered when selecting the input capacitor to ensure the

actual capacitance is never less than 0.7 µF over the entire operating range.

8.2.2.6 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 mΩ to 40 mΩ, which easily meets the ESR

requirement for stability for the LP5907.

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 increases about

2:1 as the temperature goes from 25°C down to –40°C, so some guard band must be allowed.

8.2.2.7 Remote Capacitor Operation

The LP5907 requires at least a 1-µF capacitor at the OUT pin, but there is no strict requirements about the

location of the capacitor in regards to the pin. In practical designs the output capacitor may be located up to 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.

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