LM2757TMEV

User's Guide SNVA293A – February 2008 – Revised April 2013 AN-1731 LM2757 Evaluation Board 1 General Description This evaluation board is for the testing and evaluation of the LM2757 IC. A voltage supply is the only input needed to operate the device. To measure electrical quantities, however, test or measuring equipment (mutlimeters, oscilloscopes, and so forth) is needed. 2 Schematic VOUT = 4.1V (100 mA), 4.5V (110 mA) 5.0V (180 mA) VIN = 3.0V - 5.5V CIN 1 F C1 0.47 F B2,B3 VIN A3 C1+ B1 A1 VOUT 1.0 F C1C2+ M1 C3 C2- COUT LM2757 M0 C2 0.47 F A2 GND D3 D2 C1,C2 *Bump D1 is (NC) No Connect 3 Bill of Materials (BOM) Component Symbol Value Package [U.S. (Metric)] Dimensions (mm) Temperature Characteristic Manufacturer Part No LM2757 -- DSBGA-12 0.4mm Pitch 1.2 x 1.6 x 0.6 -- National LM2757 CIN 1.0 µF, 10 V 0603 (1608) 1.6 x 0.8 x 0.8 X5R TDK C1608X5R1A105K COUT 1.0 µF, 10 V 0603 (1608) 1.6 x 0.8 x 0.8 X5R TDK C1608X5R1A105K C1, C2 0.47 µF, 6.3 V 0402 (1005) 1 x 0.5 x 0.6 X5R TDK C1005X5R0J474K All trademarks are the property of their respective owners. SNVA293A – February 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1731 LM2757 Evaluation Board 1 LM2757 Evaluation Board Layout 4 www.ti.com LM2757 Evaluation Board Layout Figure 1. Top Layer 2 AN-1731 LM2757 Evaluation Board SNVA293A – February 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated Board Operation www.ti.com Figure 2. Bottom Layer (top view, unmirrored) 5 Board Operation 5.1 Basic Connections To operate the LM2757 evaluation board, connect a supply voltage (2.7 V-5.5 V) to the board connector VIN, and the supply ground to GND. The device shutdown and voltage modes are enabled via the jumpers on the M0 and M1 headers, according to Table 1. Table 1. Device Shutdown and Voltage Modes 5.2 M0 M1 Mode 0 (−) 0 (−) Device Shutdown, Output High Impedance 0 (−) 1 (+) 5.0 V 1 (+) 0 (−) 4.5 V 1 (+) 1 (+) 4.1 V Circuit Description The core of the LM2757 is a two-phase charge pump controlled by an internally generated nonoverlapping clock. The charge pump operates by using external flying capacitors C1, C2 to transfer charge from the input to the output. At input voltages below 3.9 V (typ.) for the 5 V mode, the LM2757 operates in a 2x gain, with the input current being equal to 2x the load current. At input voltages above 3.9 V (typ.) for the 5 V mode, the part utilizes a gain of 3/2x, resulting in an input current equal to 3/2 times the load current. For the 4.5 V mode, the LM2757 operates in a 2x gain when the input voltage is below 3.35 V (typ.) and transitions to a 3/2x gain when the input voltage is above 3.35 V (typ.). For the 4.1 V mode, the device utilizes the 3/2x gain for the entire input voltage range. SNVA293A – February 2008 – Revised April 2013 Submit Documentation Feedback Copyright © 2008–2013, Texas Instruments Incorporated AN-1731 LM2757 Evaluation Board 3 Board Operation www.ti.com The two phases of the switched capacitor switching cycle will be referred to as "phase one" and "phase two". During phase one, one flying capacitor is charged by the input supply while the other flying capacitor is connected to the output and delivers charge to the load . After half of the switching cycle [ t = 1/(2×FSW) ], the LM2757 switches to phase two. In this configuration, the capacitor that supplied charge to the load in phase one is connected to the input to be recharged while the capacitor that had been charged in the previous phase is connected to the output to deliver charge. With this topology, output ripple is reduced by delivering charge to the output in every phase. The LM2757 uses fixed frequency pre-regulation to regulate the output voltage. The input and output connections of the flying capacitors are made with internal MOS switches. Pre-regulation limits the gate drive of the MOS switch connected between the voltage input and the flying capacitors. Controlling the on resistance of this switch limits the amount of charge transferred into and out of each flying capacitor during the charge and discharge phases, and in turn helps to keep the output ripple very low. 4 AN-1731 LM2757 Evaluation Board SNVA293A – February 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. 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