LP3852, LP3855

www.ti.com

SNVS174I – FEBRUARY 2003 – REVISED FEBRUARY 2015

12.3 RFI and/or EMI Susceptibility

Radio frequency interference (RFI) and electromagnetic interference (EMI) can degrade any integrated circuit

performance because of the small dimensions of the geometries inside the device. In applications where circuit

sources are present which generate signals with significant high frequency energy content (> 1 MHz), care must

be taken to ensure that this does not affect the device regulator.

If RFI and/or EMI noise is present on the input side of the regulator (such as applications where the input source

comes from the output of a switching regulator), good ceramic bypass capacitors must be used at the IN pin of

the device.

If a load is connected to the device output which switches at high speed (such as a clock), the high-frequency

current pulses required by the load must be supplied by the capacitors on the device output. Since the bandwidth

of the regulator loop is less than 100 kHz, the control circuitry cannot respond to load changes above that

frequency. This means the effective output impedance of the device at frequencies above 100 kHz is determined

only by the output capacitor or capacitors.

In applications where the load is switching at high speed, the output of the IC may need RF isolation from the

load. It is recommended that some inductance be placed between the output capacitor and the load, and good

RF bypass capacitors be placed directly across the load.

PCB layout is also critical in high noise environments, since RFI and/or EMI is easily radiated directly into PC

traces. Noisy circuitry should be isolated from "clean" circuits where possible, and grounded through a separate

path. At MHz frequencies, ground planes begin to look inductive and RFI and/or EMI can cause ground bounce

across the ground plane.

In multi-layer PCB applications, care should be taken in layout so that noisy power and ground planes do not

radiate directly into adjacent layers which carry analog power and ground.

12.4 Power Dissipation/Heatsinking

The LP3852 and LP3855 can deliver a continuous current of 1.5 A over the full operating temperature range. A

heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of

the application. Under all possible conditions, the junction temperature must be within the range specified under

operating conditions. The total power dissipation of the device is given by:

where

•

(1)

(2)

formula:

(3)

The LP3852 and LP3855 are available in TO-220 and TO-263 packages. The thermal resistance depends on

Equation 3 is

≥ 60 °C/W for TO-220 package and ≥ 60°C/W for TO-263 package, no heatsink is needed since

these limits, a heat sink is required.

12.4.1 Heatsinking TO-220 Package

The thermal resistance of a TO-220 package can be reduced by attaching it to a heat sink or a copper plane on

package.

The heatsink to be used in the application should have a heatsink to ambient thermal resistance,

Copyright © 2003–2015, Texas Instruments Incorporated

Submit Documentation Feedback

19

Product Folder Links: LP3852 LP3855