LM2772SDEV

User's Guide SNVA286A – September 2007 – Revised April 2013 AN-1714 LM2772 Evaluation Board 1 Schematic VOUT: 1.2V VIN = 3.0V to 5.5V IOUT up to 150 mA VIN VOUT CIN 1 µF COUT 4.7 µF C1+ GND LM2772 High: ON Low: Shutdown EN C3+ C1 1 µF C1C2+ C2 1 µF C3 1 µF C3- 2 C2- LM2772 Evaluation Board Layout Figure 1. Top Layer All trademarks are the property of their respective owners. SNVA286A – September 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated AN-1714 LM2772 Evaluation Board 1 Bill of Materials (BOM) www.ti.com Figure 2. Bottom Layer (top view, unmirrored) 3 Bill of Materials (BOM) Table 1. Bill of Materials (BOM) 2 Component Symbol Value Package [U.S. (Metric)] Dimensions (mm) Temperature Characteristic LM2772 -- WSON-10 Non-Pullback 3.0 x 3.0 x 0.8 Manufacturer Part No -- Texas Instruments LM2772 CIN 1µF, 10 V 0402 (1005) 1 x 0.5 x 0.6 X5R TDK C1005X5R1A105K COUT 4.7µF, 6.3 V 0603 (1608) 1.6 x 0.8 x 0.8 X5R TDK C1608X5R0J475K C1, C2, C3 1µF, 10 V 0402 (1005) 1 x 0.5 x 0.6 X5R TDK C1005X5R1A105K AN-1714 LM2772 Evaluation Board SNVA286A – September 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Board Operation www.ti.com 4 Board Operation 4.1 Basic Connections To operate the LM2772 evaluation board, connect a supply voltage (2.7 V-5.5 V) to the board connectors VIN and GND. Connecting the EN header's center pin to ON position (VIN) enables the device, and connecting it to OFF position (GND) disables the device. 4.2 Circuit Description The core of the LM2772 is a two-phase charge pump controlled by an internally generated nonoverlapping clock. The charge pump operates by using external flying capacitors (C1, C2, C3) to transfer charge from the input to the output. At input voltages below 3.5V (typ.) the LM2772 operates in a 1/2x Gain, with the input current being equal to half the load current. At input voltages between 3.5 V to 4.6 V(typ.) the part utilizes a gain of 2/5x, with the input current equal to 2/5 the load current. At input voltages above 4.6 V (typ.) the part is in a gain of 1/3x, resulting in an input current equal to 1/3 the load current. The two phases of the switched capacitor switching cycle will be referred to as the "charge phase" and the "discharge phase". During the charge phase, flying capacitors are charged by the input supply. After half of the switching cycle [ t = 1/(2×FSW) ], the LM2772 switches to the discharge phase. In this configuration, the charge that was stored on the flying capacitors in the charge phase is transferred to the output. The LM2772 uses fixed frequency pre-regulation to regulate the output voltage to 1.2 V during moderate to high load currents. 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 the flying capacitor during the charge and discharge phases, and in turn helps to keep the output ripple very low. When output currents are low (