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LP5907

SNVS798J – APRIL 2012 – REVISED MARCH 2016

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Copyright © 2012–2016, Texas Instruments Incorporated

The maximum allowable power dissipation for the device in a given package can be calculated using Equation 1:

(1)

The actual power being dissipated in the device can be represented by Equation 2:

(2)

These two equations establish the relationship between the maximum power dissipation allowed due to thermal

consideration, the voltage drop across the device, and the continuous current capability of the device. These two

equations should be used to determine the optimum operating conditions for the device in the application.

In applications where high power dissipation and/or poor package thermal resistance is present, the maximum

as given by Equation 3:

(3)

combination of the two.

8.2.2.2 External Capacitors

Like most low-dropout regulators, the LP5907 requires external capacitors for regulator stability. The device is

specifically designed for portable applications requiring minimum board space and smallest components. These

capacitors must be correctly selected for good performance.

8.2.2.3 Input Capacitor

An input capacitor is required for stability. The input capacitor should be at least equal to, or greater than, the

output capacitor for good load transient performance. At least a 1 µF capacitor has to be connected between the

LP5907 input pin and ground for stable operation over full load current range. Basically, it is ok to have more

output capacitance than input, as long as the input is at least 1 µF.

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.

8.2.2.4 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 m

Ω 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.

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