LP3872_16 Datasheet, PDF (16/28 Pages) Texas Instruments – 1.5-A Fast Ultra-Low-Dropout Linear Regulators

LP3872, LP3875
SNVS227H – FEBRUARY 2003 – REVISED JANUARY 2015
www.ti.com
9 Power Supply Recommendations
The LP397x devices are designed to operate from an input supply voltage range of 2.5 V to 7 V. The input
supply should be well regulated and free of spurious noise. To ensure that the LP387x output voltage is well
regulated, the input supply should be at least V_OUT + 0.5 V, or 2.5 V, whichever is higher. A minimum capacitor
value of 10 μF is required to be within 1 cm of the IN pin.
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 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 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 it's capacitors fixed the problem.
Because high current flows through the traces going into V_IN and coming from V_OUT, Kelvin connect the capacitor
leads to these pins so there is no voltage drop in series with the input and output capacitors.
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