LM8850

LM8850 Evaluation Board Application Note LM8850 Evaluation Board Application Note National Semiconductor Application Note 2119 John Woodward March 30, 2011 General Description The LM8850 evaluation board is a working demonstration of a step-up DC-DC converter that has been optimized for use with a super-capacitor. The super-capacitor protects a battery from power surges and enables new high-power applications in mobile device architectures. The LM8850 creates an ideal rail from 3.6V to 5.7V from an input voltage range of 2.3V to 5.5V, VIN must be 10% lower than expected VOUT. An I2C interface controlling multiple output voltage settings, input current limits, and load currents up to 1A provides superior user flexibility. The LM8850 operates in Auto mode, where the converter is in PFM mode at light loads and switches to PWM mode at heavy loads or in forced PWM mode. Hysteretic PFM extends the battery life by reducing the quiescent current to 7µA (typ.) during light load and standby conditions. Synchronous operation provides true shutdown isolation and improves the efficiency at medium to full load conditions. High switching frequency enables smaller passive components. Internal compensation is used for a broader range of inductor and output capacitor values to meet system demand and achieve small system solution size. Typical Application Circuit with Super-Capacitor 30150501 AN-2119 © 2011 National Semiconductor Corporation 301505 www.national.com AN-2119 Connection Diagram and Package Mark Information 30150502 FIGURE 1. 9-Bump micro SMD Package Pin Descriptions Pin # A1 A2 A3 B1 B2 B3 C1 C2 C3 Name VIN SW GND SDA PG VOUT SCLK EN BAL Description Power Supply Input. Connect to input filter capacitor (see Typical Application Circuit). Switching node. Connection to the internal NFET switch and PFET synchronous rectifier. Ground Pin I2C data (Use a 2kΩ pullup resistor.) Power Good indicator Output pin. I2C Clock (Use a 2KΩ pull up resistor.) Enable pin. The device is in shutdown when voltage to this pin is < 0.4V and enabled when > 1.2V. Do not leave this pin floating. Balancing pin for active voltage balancing of super-capacitor. www.national.com 2 AN-2119 Block Diagram 30150503 Board Operation To operate the LM8850, connections to VIN, Ground and the jumper on the enable pin must be in the H position. To start out, supply 3.6V to VIN. With a valid supply, Vout should power up to 5V within 5 seconds. Once enabled, the LM8850 charges the supercapacitor utilizing all of the default settings in the registers. The I2C must be used to change the default settings and this can only be done with the LM8850 enabled. Once a register is written to, the changes will transition immediately. Every time the EN pin transitions from VIL to VIH, registers 0 and 1 are reset to their defaults settings and any settings needed bust rewritten into the appropriate registers. 3 www.national.com AN-2119 I2C-Compatible Chip Address The device address for LM8850 is 60 (HEX). Register Name CONTROL CONTROL Location 00 01 Type R/W R/W CONTROL REGISTER 0 Register Location = 00 Control Register 1 Control Register 2 Register 30150504 www.national.com 4 AN-2119 CONTROL REGISTER 1 Register Location = 01 30150505 5 www.national.com AN-2119 LM8850 Evaluation Board Schematic 30150506 There are a few solder mask openings for various supercapacitor packages. If you plan on changing to a different supercapacitor than what is initially assembled, be sure assemble using the best solder pad openings for your super- capacitor footprint. Below, in the circled areas, are the initial pads used for the TDK supercap initially assembled. If the given pads aren’t acceptable, the solder mask can be removed to expose the copper for any footprint needed. www.national.com 6 AN-2119 LM8850 Evaluation Board Layers 30150508 Top Layer 30150509 Mid- Layer 1 7 www.national.com AN-2119 30150511 Mid- Layer 2 30150510 Bottom Layer www.national.com 8 AN-2119 LM8850 Evaluation Board BOM Qty. C1 (CIN) C2 (COUT) C3 = C4 (FILTER CAP) C5 (AC FILTER CAP) L1 VDD CONNECTOR GND CONNECTOR SuperCapacitor U1 Total 1 1 2 1 1 1 1 1 1 10 Value 10 µF 4.7 µF 100 µF 100 nF 1µF 500Mf LM8850TL Part Number C1608X5R0J106M CL10A475KP8NNNB TPSC107M006R0075 CL05F104Z05NNB KSLI-252012AG-1R0 93K4533 80P3616 EDLC272020-501-2F-50 Description 0603, 6.3V, TDK 0603, 10V, SAMSUNG 0805, 10V, AVX 0402, 10V, SAMSUNG 2520, 1.5A, HITACHI NEWARK NEWARK Super Capacitor Boost Regulator 9 www.national.com LM8850 Evaluation Board Application Note Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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