LM3678SD-1.2EV

User's Guide SNVA289B – June 2008 – Revised April 2013 AN-1722 LM3678 Evaluation Board 1 Introduction The LM3678 evaluation board is a working demonstration of a synchronous buck DC-DC converter. This document contains information about the evaluation board. For more details and electrical characteristics about the converter operation, see the High-Performance Miniature 1.5-A Step-Down DC-DC Converter for Handheld Applications Data Sheet (SNVS464). 2 Operating Range • • • 3 VIN range: 2.5 V to 5.5 V Recommended load current: up to 1.5A VOUT = 0.8/1.2 V Package WSON-10 no-pullback (3mm x 3mm x 0.8mm) 4 Typical Application VIN = 2.5V to 5.5V CIN 10 PF 1 PH VDD VOUT SW VDD FB EN COUT 22 PF 0.8V/1.2V LM3678 VSELECT MODE PGOOD GND GND Figure 1. Typical Application Circuit All trademarks are the property of their respective owners. SNVA289B – June 2008 – Revised April 2013 Submit Documentation Feedback AN-1722 LM3678 Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 1 Connection Diagrams 5 www.ti.com Connection Diagrams GND 1 10 FB FB 10 1 GND GND 2 9 EN EN 9 2 GND SW 3 8 MODE MODE 8 3 SW VDD 4 7 PGOOD PGOOD 7 4 VDD VDD 5 6 VSELECT VSELECT 6 5 VDD Figure 2. Top View Figure 3. Bottom View Note: Figure 1 through Figure 3 are not to any actual scale 6 7 Pin Descriptions Pin No Name 1 GND Description 2 GND 3 SW 4 VDD 5 VDD 6 VSELECT 7 PGOOD 8 MODE 9 EN Enable Pin. The device is in shutdown mode when voltage to this pin < 0.4 V and enabled when > 1.0 V. Do not leave this pin floating. 10 FB Feedback Analog Input. Connect directly to the output filter capacitor for fixed voltage versions. DAP DAP Ground Switching node connection to the internal PFET switch and NFET synchronous rectifier. Power supply input. Connect to the input filter capacitor (Figure 1). Output Voltage Select. For Example : VSELECT = LOW VOUT = 0.8 V VSELECT = HIGH, VOUT = 1.2 V Power Good Flag. This common drain logic output is pulled to ground when the output voltage is not within ± 7.5% of regulation. Mode Control Pin: Mode = 1 selects forced PWM mode Mode = 0 selects auto PFM-PWM mode Die Attach Pad; connect the DAP to GND on PCB layout to enhance thermal performance. It should not be used as a primary ground connection. Powering the LM3678 for Bench Measurements When powering the LM3678 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 the minimum ensured operating voltage of 2.7 V is reached. The enable pin should also never exceed the input voltage. 8 Operating Information The LM3678 evaluation board is set for the following default positions: • VOUT = 1.2 V, for 0.8 V, set VSELECT pin to low via jumper • Mode = H (PWM mode), for Auto mode, set mode = Low (move jumper to inner position). • EN pin is tied to VIN via a jumper 2 AN-1722 LM3678 Evaluation Board SNVA289B – June 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Evaluation Board Layout www.ti.com 9 Evaluation Board Layout LM3678 is a four-layer board designed to maximize the performance. The top layer consists of highcurrent path and the bottom layer for low-current and logic signals path. The inner layer 1 and layer 2 are dedicated for PGND (power GND) and SGND (analog and logic GND). For optimum performance, it is recommended to separate the PGND and SGND pins and join them together at the start GND on the PCB. VSEL SYNC/ MODE EN Figure 4. Top Layer Figure 5. Mid Layer 1 SNVA289B – June 2008 – Revised April 2013 Submit Documentation Feedback Figure 6. Mid Layer 2 AN-1722 LM3678 Evaluation Board Copyright © 2008–2013, Texas Instruments Incorporated 3 Bill of Materials (BOM) for LM3678 www.ti.com Figure 7. Bottom Layer 10 Bill of Materials (BOM) for LM3678 Table 1. Bill of Materials (BOM) Component Name Manufacturer Specification Case Size NSC WSON-10 3 mm x 3 mm x 0.8 mm JMK212BJ106K 0805 (2012) LM3678 C1 = 10 µF Taiyo-Yuden C2 = 22 µF JMK212BJ226MG 0805 (2012) Taiyo-Yuden NR4012T-1RON 4 mm x 4 mm x 1.2 mm Vishay/any manufacturer 0603 0Ω Inductor R1 Table 2. Test Point 4 VSEL, Mode and EN Header 3 in Series 3 (3 x 1) VSEL, Mode and EN Jumper Female (Handle centerline) A26242–ND VIN banana jack - red Johnson Components 108–0902–001 VOUT banana jack - yellow Johnson Components 108–0907–001 GND banana jack - black Johnson Components 108–0903–001 AN-1722 LM3678 Evaluation Board SNVA289B – June 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated 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. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. 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