LP3961_15 Datasheet, PDF (19/31 Pages) Texas Instruments – LP396x 800-mA Fast Ultra-Low-Dropout Linear Regulators

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LP3961, LP3964
SNVS056J – MAY 2000 – REVISED JUNE 2015
9 Power Supply Recommendations
The LP396x devices are designed to operate from an input voltage supply range between 2.5 V and 7 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 68 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 IN, OUT, and GND pins of the LP396x 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 GND
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 LP396x 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 the IN pin and coming from the OUT pin, 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
SD
Pullup
Resistor
IN
Input
Capacitor
ERROR
Pullup
Resistor
OUT
Output
Capacitor
Ground
Figure 26. LP3961 TO-263 Package Typical Layout
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