LP3878-ADJ_15 Datasheet, PDF (17/25 Pages) Texas Instruments – Micropower 800-mA Low-Noise

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LP3878-ADJ
SNVS311D – MAY 2005 – REVISED FEBRUARY 2015
9 Power Supply Recommendations
The LP3878-ADJ is designed to operate from an input voltage supply range between 2.5 V and 16 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. An input capacitor of at least 4.7 μF is required.
10 Layout
10.1 Layout Guidelines
Good PC layout practices must be used or instability can be induced because of ground loops and voltage drops.
The input and output capacitors must be directly connected to the input, output, and ground pins of the regulator
using traces which do not have other currents flowing in them (Kelvin connect).
The best way to do this is to lay out C_IN and C_OUT near the device with short traces to the IN, OUT, and ground
pins. The regulator ground pin should be connected to the external circuit ground so that the regulator and its
capacitors have a single point ground.
It should be noted that stability problems have been seen in applications where vias to an internal ground plane
were used at the ground points of the IC and the input and output capacitors. This was caused by varying ground
potentials at these nodes resulting from current flowing through the ground plane. Using a single-point ground
technique for the regulator and its capacitors fixed the problem.
Because high current flows through the traces going into IN and coming from OUT, Kelvin connect the capacitor
leads to these pins so there is no voltage drop in series with the input and output capacitors.
10.2 Layout Example
Bypass
Capacitor
BYP
N/C
Input
Capacitor
GND
IN
S/D
N/C
R2
CFF
ADJ
R1
OUT
Output
Capacitor
10.3 Power Dissipation
The LP3878-ADJ is offered in the 8-lead SO PowerPAD or WSON surface-mount packages to allow for
increased power dissipation compared to the SO-8 and Mini SO-8. For details on thermal performance as well as
mounting and soldering specifications, refer to Application Note AN-1187, SNOA401.
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