ZHCSAW6K March 2009 – April 2019 LM2840 , LM2841 , LM2842
PRODUCTION DATA.
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.