Ground

VOUT

VIN

Input

Capacitor

Output

Capacitor

BYPASS

N/C

GROUND

IN

OUT

SHUTDOWN

SENSE

ERROR

Error Pullup

Resistor

VOUT

LP2989LV

SNVS086K – MAY 2000 – REVISED JULY 2015

www.ti.com

10 Layout

10.1 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 similarly 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.

10.2 Layout Example

Figure 16. LP2989LV Layout Example

10.2.1 Thermal Considerations

CAUTION

Due to the limited power dissipation characteristics of the available SOIC (D) and

WSON (NGN) packages, all possible combinations of output current (IOUT), input

voltage (VIN), and ambient temperatures (TA) cannot be ensured.

Power dissipation, PD is calculated from the following formula:

PD = ((VIN – VOUT) × IOUT)

(1)

The LP2989LV regulator has internal thermal limiting designed to protect the device during overload conditions.

For continuous normal conditions, the recommended maximum operating junction temperature is 125°C. It is

important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional

heat sources mounted nearby must also be considered.

For surface-mount devices, heat sinking is accomplished by using the heat-spreading capabilities of the PC

board and its copper traces. Copper board stiffeners and plated through-holes can also be used to spread the

heat generated by power devices.

16

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