LM2841 datasheet(9/20 Pages) TI

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GND

SHDN

LM2840/1/2-ADJL

3.3V OUT

4.5V to 42V IN

MA2YD26

3.4k

1.02k

CBOOT

VIN

CIN

2.2 PF

0.1 PF

15 PH

COUT

10 PF

LM2841, LM2842

www.ti.com

SNVS540H – MARCH 2009 – REVISED APRIL 2013

SCHOTTKY DIODE

The breakdown voltage rating of the diode (D1) is preferred to be 25% higher than the maximum input voltage.

The current rating for the diode should be equal to the maximum output current for best reliability in most

applications. In cases where the duty cycle is greater than 50%, the average diode current is lower. In this case it

is possible to use a diode with a lower average current rating, approximately (1-D)IOUT, however the peak current

rating should be higher than the maximum load current. A 0.5A to 1A rated diode is a good starting point.

LAYOUT CONSIDERATIONS

To reduce problems with conducted noise pick up, 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, should 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 will reduce copper trace resistance which effects

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

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

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

efficiency. The ground connection for the diode, CIN, and COUT should 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. For more detail on switching power supply layout considerations see Application Note AN-

1149: Layout Guidelines for Switching Power Supplies SNVA021.

Application Information

Figure 14. Application Circuit, 3.3V Output @ 100 mA

Table 1. Some Recommended Inductors (Others May Be Used)

Manufacturer

Inductor

Contact Information

Coilcraft

LPS4018, DO1608C, DO3308, and LPO2506 series

www.coilcraft.com

800-3222645

MuRata

LQH55D and LQH66S series

www.murata.com

Coiltronics

MP2 and MP2A series

www.cooperbussman.com

Table 2. Some Recommended Input And Output Capacitors (Others May Be Used)

Manufacturer

Capacitor

Contact Information

Vishay Sprague

293D, 592D, and 595D series tantalum

www.vishay.com

407-324-4140

Taiyo Yuden

High capacitance MLCC ceramic

www.t-yuden.com

408-573-4150

ESRD seriec Polymer Aluminum Electrolytic

Cornell Dubilier

www.cde.com

SPV and AFK series V-chip series

MuRata

High capacitance MLCC ceramic

www.murata.com

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