1

2

3

6

5

4

OUT

IN

EN

BYPASS

GND

OUT-SENSE

LP3981

www.ti.com

SNVS159H – OCTOBER 2001 – REVISED JULY 2015

10 Power Supply Recommendations

The LP3981 is designed to operate from an input voltage supply range between 2.5 V and 6 V. The input voltage

range provides adequate headroom in order for the device to have a regulated output. This input supply must be

well regulated. If the input supply is noisy, additional input capacitors with low ESR can help to improve the

output noise performance.

11 Layout

11.1 Layout Guidelines

For best overall performance, place all circuit components on the same side of the circuit board and as near as

practical to the respective LDO pin connections. Place ground return connections to the input and output

capacitor, and to the LDO ground pin as close to each other as possible, connected by a wide, component-side,

copper surface. The use of vias and long traces to create LDO circuit connections is strongly discouraged and

negatively affects system performance. This grounding and layout scheme minimizes inductive parasitics, and

thereby reduces load-current transients, minimizes noise, and increases circuit stability. A ground reference

plane is also recommended and is either embedded in the PCB itself or located on the bottom side of the PCB

opposite the components. This reference plane serves to assure accuracy of the output voltage, shield noise,

and behaves similar to a thermal plane to spread (or sink) heat from the LDO device. In most applications, this

ground plane is necessary to meet thermal requirements.

11.2 Layout Example

Figure 20. LP3981 Layout Example

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