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User's Guide
SNVA052B–May 2002–Revised April 2013
AN-1227 LM3485 Evaluation Board
1 Introduction
The LM3485 is a hysteretic P-FET buck controller that uses a pulse-frequency modulation (PFM) scheme
to regulate the output voltage. This LM3485 demo board and the recommended components are intended
to demonstrate the performance with a 3.3 V output from a 12 V source. The demo board can be used
with source voltages from 7 V to 28 V to deliver output load currents up to 1A. By changing the size of a
single resistor, regulated output voltages from 1.242 V to 5 V can be obtained.
The circuit schematic is shown in Figure 1 and the bill of materials is given in Table 1.
Figure 1. Regulator With 3.3 V Output at 0.5A
Table 1. Bill of Materials (BOM)
Code Description Manufacturer
C1 Input Capacitor CAP-Tantalum 22 µF 35 V EEJL1VD226R Panasonic
C2 Output Capacitor CAP-POSCAP 100 µF 6.3 V 6TPC100M Sanyo
C3 C
ADJ
CAP-Ceramic Chip 1nF 50 V GRM39X7R102K50 Murata
C4 C
ff
CAP-Ceramic Chip 100pF 50 V GRM39X7R101K50 Murata
D1 Catch Diode Schottky Diode 1A 30 V MBRS130T3 On Semiconductor
L1 Inductor 22 µH LQH66SN220M01L Murata
Q1 P-channel MOSFET -60 V FDC5614P Fairchild
R1 Feedback high side resistor Chip Resistor 33 KΩ MCR10EZHF3302 Rohm
R2 Feedback low side resistor Chip Resistor 20 KΩ MCR10EZHF2002 Rohm
R3 R
ADJ
Chip Resistor 24KΩ MCR10EZHF2402 Rohm
U1 Buck Controller LM3485 Texas Instruments
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SNVA052B–May 2002–Revised April 2013 AN-1227 LM3485 Evaluation Board
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