National Semiconductor Application Note 2119 John Woodward March 30, 2011 General Description 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. 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, Typical Application Circuit with Super-Capacitor LM8850 Evaluation Board Application Note LM8850 Evaluation Board Application Note 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 # Name A1 VIN Description Power Supply Input. Connect to input filter capacitor (see Typical Application Circuit). A2 SW Switching node. Connection to the internal NFET switch and PFET synchronous rectifier. A3 GND Ground Pin B1 SDA I2C data (Use a 2kΩ pullup resistor.) B2 PG B3 VOUT Output pin. C1 SCLK I2C Clock (Use a 2KΩ pull up resistor.) C2 EN 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. C3 BAL Balancing pin for active voltage balancing of super-capacitor. www.national.com Power Good indicator 2 AN-2119 Block Diagram 30150503 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. 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 3 www.national.com AN-2119 I2C-Compatible Chip Address The device address for LM8850 is 60 (HEX). Location Type CONTROL Register Name 00 R/W Control Register 1 Register CONTROL 01 R/W Control Register 2 CONTROL REGISTER 0 Register Location = 00 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- www.national.com 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. 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 Qty. Value C1 (CIN) 1 10 µF C1608X5R0J106M 0603, 6.3V, TDK C2 (COUT) 1 4.7 µF CL10A475KP8NNNB 0603, 10V, SAMSUNG C3 = C4 (FILTER CAP) 2 100 µF TPSC107M006R0075 0805, 10V, AVX C5 (AC FILTER CAP) 1 100 nF CL05F104Z05NNB 0402, 10V, SAMSUNG L1 1 1µF KSLI-252012AG-1R0 2520, 1.5A, HITACHI VDD CONNECTOR 1 - 93K4533 NEWARK GND CONNECTOR 1 - 80P3616 NEWARK SuperCapacitor 1 500Mf U1 1 Total 10 Part Number Description EDLC272020-501-2F-50 Super Capacitor LM8850TL Boost Regulator 9 www.national.com AN-2119 LM8850 Evaluation Board BOM 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 Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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