Datasheet
LM5022
www.ti.com
SNVS480G –JANUARY 2007–REVISED DECEMBER 2013
GROUND PLANE AND SHAPE ROUTING
The diagram of Figure 25 is also useful for analyzing the flow of continuous current vs. the flow of pulsating
currents. The circuit paths with current flow during both the on-time and off-time are considered to be continuous
current, while those that carry current during the on-time or off-time only are pulsating currents. Preference in
routing should be given to the pulsating current paths, as these are the portions of the circuit most likely to emit
EMI. The ground plane of a PCB is a conductor and return path, and it is susceptible to noise injection just as
any other circuit path. The continuous current paths on the ground net can be routed on the system ground plane
with less risk of injecting noise into other circuits. The path between the input source, input capacitor and the
MOSFET and the path between the output capacitor and the load are examples of continuous current paths. In
contrast, the path between the grounded side of the power switch and the negative output capacitor terminal
carries a large pulsating current. This path should be routed with a short, thick shape, preferably on the
component side of the PCB. Multiple vias in parallel should be used right at the negative pads of the input and
output capacitors to connect the component side shapes to the ground plane. Vias should not be placed directly
at the grounded side of the MOSFET (or R
SNS
) as they tend to inject noise into the ground plane. A second
pulsating current loop that is often ignored but must be kept small is the gate drive loop formed by the OUT and
VCC pins, Q1, R
SNS
and capacitor C
F
.
Table 1. BOM for Example Circuit
ID Part Number Type Size Parameters Qty Vendor
U1 LM5022 Low-Side Controller VSSOP-10 60V 1 NSC
Q1 Si4850EY MOSFET SO-8 60V, 31mΩ, 27nC 1 Vishay
D1 CMSH2-60M Schottky Diode SMA 60V, 2A 1 Central Semi
L1 SLF12575T-M3R2 Inductor 12.5 x 12.5 x 7.5 mm 33µH, 3.2A, 40mΩ 1 TDK
Cin1, Cin2 C4532X7R1H475M Capacitor 1812 4.7µF, 50V, 3mΩ 2 TDK
Co1, Co2 C5750X7R2A475M Capacitor 2220 4.7µF,100V, 3mΩ 2 TDK
Cf C2012X7R1E105K Capacitor 0805 1µF, 25V 1 TDK
Cinx
C2012X7R2A104M Capacitor 0805 100nF, 100V 2 TDK
Cox
C1 VJ0805A561KXXAT Capacitor 0805 560pF 10% 1 Vishay
C2 VJ0805Y124KXXAT Capacitor 0805 120nF 10% 1 Vishay
Css VJ0805Y103KXXAT Capacitor 0805 10nF 10% 1 Vishay
Ccs VJ0805Y102KXXAT Capacitor 0805 1nF 10% 1 Vishay
R1 CRCW08053011F Resistor 0805 3.01kΩ 1% 1 Vishay
Rfb1 CRCW08056490F Resistor 0805 649Ω 1% 1 Vishay
Rfb2 CRCW08052002F Resistor 0805 20kΩ 1% 1 Vishay
Rs1 CRCW0805101J Resistor 0805 100Ω 5% 1 Vishay
Rs2 CRCW08053571F Resistor 0805 3.57kΩ 1% 1 Vishay
Rsns ERJL14KF10C Resistor 1210 100mΩ, 1%, 0.5W 1 Panasonic
Rt CRCW08053322F Resistor 0805 33.2kΩ 1% 1 Vishay
Ruv1 CRCW08052611F Resistor 0805 2.61kΩ 1% 1 Vishay
Ruv2 CRCW08051002F Resistor 0805 10kΩ 1% 1 Vishay
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