LM8850 NSC | Alldatasheet
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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 su- perior user flexibility. The LM8850 operates in Auto mode, where the converter is in PFM mode at light loads and switch- es to PWM mode at heavy loads or in forced PWM mode. Hysteretic PFM extends the battery life by reducing the qui- escent 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 compo- nents. 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 © 2011 National Semiconductor Corporation 301505 www.national.com LM8850 Evaluation Board Application NoteAN-2119
FIGURE 1. 9-Bump micro SMD Package A1 VIN 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. when > 1.2V. Do not leave this pin floating. C3 BAL Balancing pin for active voltage balancing of super-capacitor.
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 uti- lizing 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 Location Type Register CONTROL 00 R/W Control Register 1 CONTROL 01 R/W Control Register 2 CONTROL REGISTER 0 Register Location = 00 30150504 www.national.com 4 AN-2119
Register Location = 01 30150505 5 www.national.com AN-2119
There are a few solder mask openings for various superca- pacitor packages. If you plan on changing to a different su- percapacitor 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 re- moved 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
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LM8850 Evaluation Board BOM Qty. Value Part Number Description 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 EDLC272020-501-2F-50 Super Capacitor U1 1 LM8850TL Boost Regulator Total 10 9 www.national.com AN-2119
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