LP3910 Datasheet, PDF (68/72 Pages) Texas Instruments – Power Management IC for Hard-Drive-Based Portable Media Players

LP3910
SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015
100
V_IN = 2.7 V
90
80
70
VIN = 3.6 V
VIN = 4.2 V
60
V_OUT = 3.3 V
50
0.1
1.0
10
100
OUTPUT CURRENT (mA)
L = 2.2 μH
1000
PFM-to-PWM Mode
Figure 83. Buck2 Efficiency vs Output Current
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10 Power Supply Recommendations
The LP3910 is designed to use a standard single-cell lithium-ion or lithium-polymer battery. Battery voltage
maximum operating voltage can be up to 4.5 V. The LP3910 can also use an AC-DC wall adapter as a charging
source up to 6 V or a USB source of at least 4.25 V. The USB charging source must supply charging currents of
100 mA, 500 mA, or 800 mA.
11 Layout
11.1 Layout Guidelines
For good performance of the circuit, it is essential to place the input and output capacitors very close to the
circuit, using wide routing for the traces to allow high currents. Sensitive components must be placed far from
those components with high pulsating current, and decoupling capacitors must be placed close to circuit VIN
pins. Digital and analog grounds must be routed separately and connected together in a star connection. It is
good practice to minimize high current and switching current paths.
11.1.1 LDO Regulators
Place the filter capacitors very close to the input and output pins. Use large trace width for high current-carrying
traces and the returns to ground.
11.1.2 Buck and Buck-Boost Regulators
Place the supply bypass, filter capacitor, and inductor close together, keeping the traces short. The traces
between these components carry relatively high switching current and act as antennas. Following these rules
reduces radiated noise. Arrange the components so that the switching current loops curl in the same direction.
Connect the buck ground and the ground of the capacitors together using generous component-side copper fill
as a pseudo-ground plane. Connect the grounds to the general board system ground plane at a single point.
Place the pseudo-ground plane below these components and then have it tied to system ground of the output
capacitor outside of the current loops. This prevents the switched current from injecting noise into the system
ground. These components, along with the inductor and output, must be placed on the same side of the circuit
board, and their connections must be made on the same layer.
Route the noise sensitive traces such as the voltage feedback path away from the inductor. This is done by
routing it on the bottom layer or by adding a grounded copper area between switching node and feedback path.
Noisy traces between the power components and keep any digital lines away from this section. Keep the
feedback node as small as possible so that the ground pin and ground traces shield the feedback node from the
SW or buck output.
Use wide traces between the power components and for power connections to the DC-DC converter circuit. This
reduces voltage errors caused by resistive losses.
68
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