LM3674MF-1.8EV

User's Guide SNVA139K – January 2006 – Revised April 2013 AN-1427 LM3674 Evaluation Board 1 Introduction The LM3674 evaluation board is a working demonstration of a step down DC-DC converter. This document contains information about the evaluation board. For further information on buck converter topology, device electrical characteristics, and component selection, see the device-specific data sheet. 2 General Description The LM3674 converts high input voltages to lower output voltages with high efficiency through an inductor based switching topology. The device operates at a fixed-frequency of 2 MHz (typ.) providing high efficiency during pulse width modulation (PWM) mode. The LM3674 is available in both fixed and adjustable output voltage options ranging from 1.0 V to 3.3 V in a SOT23-5 package. 3 Operating Conditions • • • • 4 VIN range: 2.7 V ≤ VIN ≤ 5.5 V Recommended load current: 0 mA ≤ IOUT ≤ 600 mA Ambient temperature (TA) range: -30°C to +85°C Junction temperature (TJ) range: -30°C to +125°C Typical Application VIN 2.7V to 5.5V L1: 2.2 PH VIN 1 CIN 4.7 PF VOUT SW 5 COUT 10 PF LM3674 GND 2 EN FB 3 4 Figure 1. Typical Application Circuit: Fixed Voltage VIN L1: 2.2 PH VIN 2.7V to 5.5V 1 GND VOUT SW LM3674ADJ CIN 4.7 PF 5 C1 R1 C2 R2 COUT 10 PF 2 EN FB 3 4 Figure 2. Typical Application Circuit: Adjustable Voltage All trademarks are the property of their respective owners. SNVA139K – January 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated AN-1427 LM3674 Evaluation Board 1 Output Voltage Selection for LM3674MF-ADJ 5 www.ti.com Output Voltage Selection for LM3674MF-ADJ The output voltage of the adjustable parts can be programmed through the resistor network connected from VOUT to FB to GND. The resistor from FB to GND (R2) should be 200 kΩ to keep the current drawn through this network small, but large enough that it is not susceptible to noise. If R2 is 200 kΩ, and given the VFB is 0.5 V, then the current through the resistor feedback network will be 2.5 µA. The output voltage formula is: VOUT = VFB R1 (R ) +1 2 (1) VOUT: output voltage (V) VFB: feedback voltage (0.5 V typical) R1: feedback resistor from VOUT to FB (Ω ) R2: feedback resistor from FB to GND (Ω) For the fixed output voltage parts the feedback resistors are internal. Place a 0 Ω resistor for R1. The bypass capacitors C1 and C2 (labeled C3 and C4 on Evaluation Board) in parallel with the feedback resistors are chosen for stable operation. Below are the formulas for C1 and C2. C1 = 1 2 x S x R1 x 45 kHz (2) 1 C2 = 2 x S x R2 x 45 kHz (3) Table 1. LM3674-ADJ Configurations for Various Vout (Circuit of Figure 2) 6 VOUT (V) R1(kΩ ) R2(kΩ ) C1(pF) C2(pF) L (µH) CIN (µF) COUT (µF) 1.0 200 200 18 None 2.2 4.7 10 1.1 191 158 18 None 2.2 4.7 10 1.2 280 200 12 None 2.2 4.7 10 1.5 357 178 10 None 2.2 4.7 10 1.6 442 200 8.2 None 2.2 4.7 10 1.7 432 178 8.2 None 2.2 4.7 10 1.8 464 178 8.2 None 2.2 4.7 10 1.875 523 191 6.8 None 2.2 4.7 10 2.5 402 100 8.2 None 2.2 4.7 10 2.8 464 100 8.2 33 2.2 4.7 10 3.3 562 100 6.8 33 2.2 4.7 10 Powering the LM3674 for Bench Measurement When powering the LM3674 with a bench power supply, it is recommended to place a 100 µF tantalum capacitor across the VIN and GND supply terminals of the bench power supply. This capacitor reduces the input spike caused by the power supply and long power cables. The combination of the power supply and inductance within the power cables produce a large voltage spike that may damage the device. In addition, consideration must be given to the enable pin of the device. The enable should never be taken high, until minimum specified operating voltage of 2.7 V is reached. The enable pin should also never exceed the input voltage. 2 AN-1427 LM3674 Evaluation Board SNVA139K – January 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Connection Diagram and Package Mark Information www.ti.com 7 Connection Diagram and Package Mark Information SW 5 VIN 1 FB 4 GND 2 EN 3 Figure 3. SOT23–5 Package, Top View 8 Pin Descriptions (SOT23-5) Table 2. Pin Descriptions Pin No Name Description 1 VIN Power supply input. Connect to the input filter capacitor (Figure 1) 2 GND Ground pin 3 EN Enable input. The device is in shutdown mode when voltage to this pin is 1.0 V. Do not leave this pin floating. 4 FB Feedback analog input. Connect directly to the output filter capacitor for fixed voltage versions. For adjustable version external resistor dividers are required (Figure 2). The internal resistor dividers are disabled for the adjustable version. 5 SW Switching node connection to the internal PFET switch and NFET synchronous rectifier. SNVA139K – January 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated AN-1427 LM3674 Evaluation Board 3 Evaluation Board Layout 9 www.ti.com Evaluation Board Layout Figure 4. Top Layer (SOT23-5) Figure 5. Bottom Layer (SOT23-5) 4 AN-1427 LM3674 Evaluation Board SNVA139K – January 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Evaluation Board Layout www.ti.com Table 3. Bill of Materials (BOM) For Common Configurations Manufacture Manufacture No Description LM3674 - 1.5 V and 1.8 V FIXED C1 (input C) TDK C2012XR0J475K 4.7 µF, 6.3 V, 0805, 10% C2 (output C) TDK C2012X5R0J106K 10 µF, 6.3 V, 0805, 10% L1 (inductor) Coilcraft DO3314-222MX 2.2 µH inductor, 1.6A sat R1 (VOUT to VFB ) Vishay CRCW06030R00F 0 Ω, 0603, 1% R2 (VFB to GND) None C3 (VOUT to VFB ) None C4 (VFB to GND) None LM3674 - 3.3 V ADJUSTABLE C1 (input C) TDK C2012XR0J475K 4.7 µF, 6.3 V, 0805, 10% C2 (output C) TDK C2012X5R0J106K 10 µF, 6.3 V, 0805, 10% L1 (inductor) Coilcraft DO3314-222MX 2.2 µH inductor, 1.6A sat R1 (VOUT to VFB ) Vishay CRCW06034643F 562 kΩ, 0603, 1% R2 (VFB to GND) Vishay CRCW06031783F 100 kΩ, 0603, 1% C3 (VOUT to VFB ) Vishay VJ0603A6R8KXAA 6.8 pF, 0603, 10% C4 (VFB to GND) Vishay VJ0603A8R2KXAA 33 pF , 0603, 10% COMMON TO ALL VIN banana jack - red Johnson Components 108-0902-001 Connector, insulated banana jack (red) VOUT banana jack - yellow Johnson Components 108-0907-001 Connector, insulated banana jack (yellow) GND banana jack - black Johnson Components 108-0903-001 Connector, insulated banana jack (black) Post for EN Turrent 1573-2 Upright post from evaluation board Post for VIN Turrent 1502-2 Upright post from evaluation board Post for VOUT Turrent 1502-2 Upright post from evaluation board Post for GND Turrent 1502-2 Upright post from evaluation board SNVA139K – January 2006 – Revised April 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated AN-1427 LM3674 Evaluation Board 5 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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