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LM2840-Q1, LM2841-Q1, LM2842-Q1

SNVSBE5 – APRIL 2019

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Product Folder Links: LM2840-Q1 LM2841-Q1 LM2842-Q1

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Copyright © 2019, Texas Instruments Incorporated

9 Power Supply Recommendations

The LM284x-Q1 are designed to operate from an input voltage supply range between 4 V and 42 V. This input

supply must be able to withstand the maximum input current and maintain a voltage above 4.5 V. The resistance

of the input supply rail must be low enough that an input current transient does not cause a drop at the device

supply voltage high enough to cause a false UVLO fault triggering and system reset. If the input supply is located

more than a few inches from the device, additional bulk capacitance may be required in addition to the ceramic

input capacitors.

10 Layout

10.1 Layout Guidelines

To reduce problems with conducted noise pickup, the ground side of the feedback network should be connected

directly to the GND pin with its own connection. The feedback network, resistors R1 and R2, must be kept close

to the FB pin, and away from the inductor to minimize coupling noise into the feedback pin. The input bypass

capacitor CIN must be placed close to the VIN pin. This reduces copper trace resistance, which effects input

voltage ripple of the IC. The inductor L1 must be placed close to the SW pin to reduce EMI and capacitive

coupling. The output capacitor, COUT must be placed close to the junction of L1 and the diode D1. The L1, D1,

and COUT trace must be as short as possible to reduce conducted and radiated noise and increase overall

efficiency. The ground connection for the diode, CIN, and COUT must be as small as possible and tied to the

system ground plane in only one spot (preferably at the COUT ground point) to minimize conducted noise in the

system ground plane. See Layout Guidelines for Switching Power Supplies for more detail on switching power

supply layout considerations.

10.2 Layout Example

Figure 17. Recommended Layout