TC3827 Lithium-Ion Battery Charger FEATURES GENERAL DESCRIPTION ■ ■ ■ ■ ■ ■ ■ ■ ■ The TC3827 is a battery charger controller for a single cell Li-Ion battery. Using an external PMOS transistor, safe and fast charging of a single Li-Ion cell is accomplished. Features include over-current foldback, charge current monitor, and charge status LED indicator output. An overall system accuracy of 1% ensures that the cell capacity is fully utilized without cycle life degradation. An external resistor sets charge current. The TC3827 operates with an input voltage range from 4.5V to 5.5V. It is specified over the ambient operating temperature range of –20°C to +85°C and is available in a space-saving 8-Pin MSOP. Low Power Dissipation Shutdown Current: 1µA (Typical) Space-Saving 8-Pin MSOP Package No Inductor Required 1% Overall System Accuracy Charge Current Monitor Output Charge Status Indicator Output Foldback Current Limiting –20°C to +85°C Ambient Operating Temperature Range TYPICAL APPLICATIONS ■ ■ ■ ■ ■ ■ ■ ■ PDAs Cradle Chargers Li-Ion Battery Chargers Desktop Computers Hand-Held Instruments Cellular Telephones Battery Operated Devices Self-Charging Battery Packs ORDERING INFORMATION Part No. Package Temperature Range TC3827-4.1VUA TC3827-4.2VUA 8-Pin MSOP 8-Pin MSOP –20°C to +85°C –20°C to +85°C FUNCTIONAL BLOCK DIAGRAM PIN CONFIGURATION 8-Pin MSOP 8 VIN SHDN 1 7 VSNS GND 2 MODE 3 IMON TC3827 + VSNS – 5 VOUT IMON K C/A 6 VDRV 4 VIN GND + E/A – TYPICAL APPLICATION CIRCUIT CONTROL BLOCK MODE + VOUT NDP6020P PMOS RSENSE VDRV E/A VREF – +5 VIN 10µF SHDN LED VIN VSNS TC3827 VDRV VOUT MODE IMON SHDN MODE IMON SHDN + TC3827 22µF Li-Ion – GND Controller Figure 1. TC3827 Typical Application Circuit © 2001 Microchip Technology Inc. DS21558A TC3827-2 12/12/00 Lithium-Ion Battery Charger TC3827 ABSOLUTE MAXIMUM RATINGS* IMODE (sink) .............................................................. 20mA IDRV ............................................................................1mA ESD Rating ................................................................. 2kV Input Voltage (VIN), VOUT, VSNS, MODE, and IMON ........... .............................................................. –0.3V to 6.0V SHDN ...............................................–0.3V to (VIN + 0.3V) 8-Pin MSOP (derate 4.1mW/°C above +70°C) ..... 330mW Operating Ambient Temperature Range .. –20°C to +85°C Storage Temperature Range ................. –65°C to +150°C Lead Temperature (Soldering, 10 sec) ................. +300°C Vapor Phase (60 sec) ........................................... +210°C Infrared (15 sec) .................................................... +220°C IIMON (source) ......................................................0.375mA *Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS: VIN = [VREG + 1V] , TA = -20°C to +85°C, unless otherwise noted. Typical values at TA = +25°C, RSENSE = 500mΩ, Test Circuit Figure 3. Symbol Parameter Test Conditions Min Typ Max Units IVIN Power Supply Current Shutdown Mode, VSHDN = 0V Constant Voltage Mode — — 4.5 1 350 — 15 560 5.5 µA — — –1 –10 –1 — 4.2 4.1 — — ±0.2 1 — — +1 +10 +1 5 V — 0.08 — — — 1.0 1 — — mA — 40 — — 100 53 46 0.46 — 75 — — dB mV mA A/A — — — VREG — — — 400 +1 V mV µA 40 – — — — — — 25 +1 %VDD %VDD µA — 26 — V/V VIN Power Supply Voltage In Voltage Regulation (Constant Voltage Mode) VREG Battery Regulation Volts 3827- 4.2VUA 3827- 4.1VUA VOUT Output Voltage Accuracy VIN = VREG + 1V to 5.5V, LIREG Line Regulation VIN = 4.5V to 5.5V, IOUT = 75mA LDREG Load Regulation IOUT =10mA to 75mA IDISCH Output Reverse Leakage VIN = Floating, VOUT = VREG MOSFET Gate Drive IDRV Gate Drive Current Sink, Constant Voltage Mode (Note 1) Source, Constant Voltage Mode (Note 1) VDRV Gate Drive Min Voltage Current Sense Amp VGAIN GAIN (∆VGS/∆VOUT) VCS Current Limit Threshold (VIN – VSNS) @ IMAX ISC Short Circuit Current K KFactor MODE VTH Mode Threshold VOL Mode Low Voltage ISINK = 10mA, VOUT = 3.5V ILK Mode Leakage Current VMODE = 5.5V, IO = 0mA, MODE = Constant Voltage SHDN VIH SHDN High Threshold VIL SHDN Low Threshold ILK SHDN Leakage Current VSHDN = 0V to 5V IMON ∆VIMON Current Sense Gain VO = 0V to 3.5V,RL > 20kΩ ∆(VIN - VSNS) V % mV mV µA V Notes: 1. Where VOUT = 1% from Nominal, continuous current. TC3827-2 12/12/00 2 © 2001 Microchip Technology Inc. DS21558A Lithium-Ion Battery Charger TC3827 PIN DESCRIPTION Pin No. 8-Pin MSOP 1 2 3 4 5 6 7 8 Symbol SHDN GND MODE IMON VOUT VDRV VSNS VIN Type Signal Input Power Signal Output Voltage Output Voltage Input Signal Output Signal Input Power Description Shutdown Input System Ground Charge Mode Indicator Buffered Copy of Current Sense Resistor Drop Charger DC Output Voltage Sense Gate Drive to External MOSFET Current Sense Voltage Input Charger DC Input Voltage I/O DESCRIPTION SHDN: When SHDN is low, VDRV is pulled high to VIN and the charge is interrupted. GND: Connect to the battery’s negative terminal. See Layout Guidelines for information on system grounding. VOUT: Battery positive terminal and charger regulated output voltage.This pin is connected to the external PMOS drain and directly to the load for optimal regulation. VOUT pin draws typically 1µA from the battery when VIN power is removed. Requires a Bypass capacitor. MODE: Charge Status Indicator. Mode is an open-drain, N-channel MOSFET capable of sinking 20mA for an LED status indication of charger in current limited mode. LED is off in current-voltage mode. VDRV: Gate drive output for the external PMOS pass device. IMON : Battery Charge current profile. This output is an amplified copy of the voltage drop across the current sense resistor. It can be used as input to an A/D converter to provide the controller with information about the charge current profile. VIN: Charger power supply input (+6V absolute max.). Bypass to GND with a capacitor. VSNS: Battery charge current sense voltage feedback. This voltage is developed across a small value precision resistor that is in series with the battery. FUNCTIONAL DESCRIPTION of the IC need a suitable bypass capacitor. The TC3827 also has a logic-level shutdown input, SHDN, which may be connected to the input voltage to enable the IC. Pulling it “low” or to ground will disable the PMOS drive (VDRV pulled up to VIN voltage). Also, a charger mode pin (MODE) is provided to drive an optional LED for a visual indication of current limited mode operation. LED will be turned off in constant voltage mode operation. The TC3827 controller only requires a P-channel power MOSFET and two small capacitors to perform as an inexpensive Li-Ion battery charger. The TC3827 controller drives an external PMOS to provide a regulated output current to charge the battery. Initially, current limited charging occurs until a pre-specified battery voltage is measured at the VOUT pin. It then switches to constant-voltage mode. During constant-voltage mode the TC3827 works like a linear regulator, holding the output voltage within the specified accuracy. The charger output is sensed at the VOUT pin. The charging current follows the foldback characteristic as shown in Figure 2. The sense resistor sets the maximum charging current, IMAX. The voltage drop across the current sense resistor is sensed at the VSNS input. An amplified copy of this sense voltage is provided as output on the current monitor pin (IMON). When the battery is deeply discharged to a minimum voltage level, or if the battery is shorted, the current sense circuit folds back the charge current to limit the power dissipation of the PMOS. Both the VIN and VOUT pins © 2001 Microchip Technology Inc. DS21558A 3 TC3827-2 12/12/00 Lithium-Ion Battery Charger TC3827 APPLICATIONS INFORMATION The charge current profile can be monitored using the voltage signal at IMON. The use of an LED as a status indicator is optional. The application circuit is shown in Figure 1. A typical Li-Ion cell should be charged at a controlled current until it reaches 4.1V or 4.2V (depending on the type of cell), then charged at this voltage. The TC3827 is designed to offer the maximum integration and function with a small application circuit. The only necessary external components are a PMOS , two small capacitors, and an RSENSE. VOUT R SENSE=500mΩ VREG IREG Constant Voltage Mode Foldback Current Limited Mode VIN IMAX S D 10µF G VSNS VIN VDRV VOUT IFOLDBACK ISC NDP6020P PMOS MODE TC3827 IMON VOUT 22µF GND SHDN IOUT Figure 2. TC3827 Charging Characteristic Figure 3. TC3827 Test Circuit SELECTING EXTERNAL COMPONENTS CHARGER MODES DESCRIPTION Power Supply Input Initiating a Charge Cycle In most applications, this will be a small “wall cube” switching converter with an output voltage limit range of 5V to 6V. The TC3827 initiates a charge upon toggling the shutdown pin high, insertion of the battery or application of an external power source. The TC3827 provides a foldback current limited charge where an external current sense resistor sets IMAX. The voltage drop across the current sense resistor is applied to the VIN -VSNS pins and presented to the current limited control-loop.The current loop will protect a deeply discharged (or shorted) battery by folding back the current limited charge, and reduces the power dissipation in PMOS. P-Channel Pass Device The PMOS is used to regulate current from the source into the Li-Ion cell. Specifications to consider when choosing an appropriate PMOS are the minimum drain-source breakdown voltage, the minimum turn-on threshold voltage (VGSTH), drain current and power-dissipation capabilities. Current Limited, Constant-voltage Charge Cycle Bypass Capacitors Bypass VIN with a capacitor value of at least 10µF. Bypass VOUT with a capacitor value of at least 1µF. TC3827-2 12/12/00 The TC3827 begins to charge the Li-Ion cell by turning on the external PMOS. The charge continues until the battery voltage rises to the lithium-ion cell voltage of 4.2V or 4.1V (depending on type of cell). As the battery voltage reaches the regulated output voltage, the internal feedback 4 © 2001 Microchip Technology Inc. DS21558A Lithium-Ion Battery Charger TC3827 control loop changes from current limiting to voltage regulation. If an external micro-controller determines battery conditions are unsafe for charge it can toggle the shutdown pin low and interrupt the charge cycle. Otherwise, once the predetermined cell voltage is reached the TC3827 shifts into a constant-voltage mode (linear regulation) and a variable charge current is applied as required to maintain the battery cell voltage to within 1% accuracy of the cell voltage setpoint. Higher Current Option The current sense resistor for the circuit shown in Figure 1 is calculated by: RSENSE = VCS /IMAX . Where VCS is the current limit threshold voltage of 40mV to 75mV, 50mV typical. If IMAX = 1A is desired, RSENSE = 50mΩ. Pre-regulated Input Voltage (5V ± 0%) For this application, the required θJA thermal impedance is calculated as follows: IMON – Charge Current Status The IMON pin provides an output voltage that is proportional to the battery charging current . It is an amplified version of the sense resistor voltage drop that the current loop uses to control the PMOS device. This voltage signal can be applied to the input of an A/D Converter and used by a controller to display information about the state of the battery or charge current profile. if: then: TJMAX – TAMAX = 150°C – 50°C = 100°C. MODE – Charge Mode Status LED The MODE pin indicates the battery charging mode. An LED can be connected to the MODE for a visible indicator. Alternatively, a pull-up resistor (typically 100kΩ) from the interfacing logic supply to MODE provides a logic-level output. The MODE pin will toggle LOW and the LED will illuminate when the charger is in the current limited mode. The MODE pin toggles to a high impedance state and the LED will be off during constant-voltage mode charging or if the battery is not connected. The MODE pin toggles at a VOUT of VREG, typically. θJA = ∆T/(IOx k x VIN) = 100/(1 x 0.46 x 5.5) = 39.5 °C/W This k factor is: k = ISC/IMAX ≈ 0.46. This thermal impedance can be realized using the transistor shown in Figure 1 when mouted to a heat sink. The θSA or thermal impedance of a suitable heatsink is calculated below: APPLICATION CIRCUIT DESIGN θSA ≤ (θJA – θJC – θCS) = 39.5 – 2.5 – 0.3 = 36.7°C/W Due to the low efficiency of Linear Regulator Charging, the most important factors are thermal design and cost, which is a direct function of the input voltage, output current and thermal impedance between the PMOS and the ambient cooling air. The worst-case situation is when the battery is shorted since the PMOS has to dissipate the maximum power. A tradeoff must be made between the charge current, cost and thermal requirements of the charger. Higher current requires a larger PMOS with more effective heat dissipation leading to a more expensive design. Lowering the charge current reduces cost by lowering the size of the PMOS, possibly allowing a smaller package such as 6-Pin SOT. The following designs consider both options. © 2001 Microchip Technology Inc. DS21558A the PMOS data sheet allows a max junction temperature of TJMAX = 150°C, at 50°C ambient with convection cooling, the maximum allowed junction temperature rise is: Where the θJC, or junction-to-case thermal impedance is for the PMOS from the PMOS data sheet. A low cost heatsink is Thermalloy type PF430, with a θSA = +25.3°C/W. 5 TC3827-2 12/12/00 Lithium-Ion Battery Charger TC3827 Lower Current Option RDS(ON) = VDS/IMAX ≤ 0.725V/1A = 725mΩ Preregulated Input Voltage (5V +/- 10%) The selected PMOS must satisfy these criteria. If lower charging current is allowed, the ΘJA value can be increased, and the system cost decreased. This is accomplished by using a FDC638P PMOS, for example, in a 6-Pin SOT package mounted on a small 1in x 1in area of 2oz Cu on FR-4 board. This provides a convection cooled thermal impedance of ΘJA = +78°C/W. Allowing a maximum FET junction temperature of +150°C, at +50°C ambient, with convection cooling the maximum allowed heat rise is: 150°C–50°C = 100°C. External Capacitors The TC3827 is stable with or without a battery load, and virtually any good quality output filter capacitors can be used, independent of the capacitor’s minimum ESR (Effective Series Resistance) value. The actual value of the capacitor and its associated ESR depends on the gm and capacitance of the external PMOS device. A 22µF tantalum or aluminum electrolytic capacitor at the output is sufficient to ensure stability for up to a 10A output current. The maximum short circuit current, ISC, is found as: Shutdown Mode ISC = ∆T/(ΘJA x VIN) = 100/(78 x 5.5) = 0.23A Applying a logic high signal to the SHDN pin or tying it to the input pin will enable the output. Pulling this pin low or tying it to ground will disable the output. In shutdown mode, the controller’s quiescent current is reduced to typically 1µA. Thus the maximum charging current, IMAX, is: IMAX = ISC/k = 0.51A Short Circuit Protection The current sense resistor for this application is then: The PMOS is protected during short circuit conditions with a foldback type of current limiting that reduces the power dissipation. RSENSE = VCS/IMAX = 0.05/0.51 = 98mΩ ≈ 100mΩ FET Selection Current Sense Resistor The type and size of the pass transistor is determined by the threshold voltage, input-output voltage differential and load current. The selected PMOS must satisfy the physical and thermal design requirements. To ensure that the maximum VGS provided by the controller will turn on the FET at worst case conditions, (i.e., temperature and manufacturing tolerances) the maximum available VGS must be determined. Maximum VGS is calculated as follows: The current limit sense resistor, RSENSE, is calculated previously. Proper de-rating is advised to select the power dissipation rating of the resistor. The simplest and cheapest sense resistor for high current applications, is a PCB trace. However, the temperature dependence of the copper trace and the thickness tolerances of the trace must be considered in the design. Copper’s Tempco, in conjunction with the proportionalto-absolute temperature (±0.3%) current limit voltage, can provide an accurate current limit. Alternately, an appropriate sense resistor, such as surface mount sense resistors, available from KRL, can be used. VGSMAX = VIN – (IMAX x RSENSE) – VDRVMAX For example: VIN = 5V, and IMAX = 1A, PCB Layout Issues VGSMAX = 5V - (1A x 50mΩ) – 1V= 3.95V For optimum voltage regulation, place the load as close as possible to the device’s VOUT and GND pins. It is recommended to use dedicated PCB traces to connect the PMOS drain to the positive terminal and VSS to the negative terminal of the load to avoid voltage drops along the high current carrying PCB traces. If the PCB layout is used as a heatsink, adding many vias around the power FET helps conduct more heat from the FET to the back-plane of the PCB, thus reducing the maximum FET junction temperature. The difference between VIN and VO (VDS) must exceed the voltage drop due to the sense resistor plus the ONresistance of the PMOS at the maximum charge current. VDS ≤ VIN – VO – VCS = 5V – 4.2V – 0.075V = 0.725V The maximum RDS(ON) required at the available gate drive (VDR) and Drain-to-Source voltage (VDS) is: TC3827-2 12/12/00 6 © 2001 Microchip Technology Inc. DS21558A Lithium-Ion Battery Charger TC3827 TYPICAL CURVES VOUT vs ILOAD (VIN=5.1V) VOUT vs VIN (ILOAD=1A) 4.110 4.110 4.105 VOUT - V VOUT - V 4.105 4.100 4.100 4.095 4.095 4.090 4.090 0 200 400 600 800 1000 4.5 4.6 4.7 4.8 4.9 ILOAD - mA 5.1 5.2 5.3 5.4 5.5 Figure. 5 Figure. 4 IGND vs VIN (ILOAD=10mA) VOUT vs VIN (ILOAD=10mA) 4.110 5.0 VIN - V 0.300 0.290 0.280 IGND - mA VOUT - V 4.105 4.100 0.270 0.260 0.250 0.240 0.230 4.095 0.220 0.210 4.090 4.5 0.200 4.6 4.7 4.8 4.9 5.0 VIN - V 5.1 5.2 5.3 5.4 4.5 5.5 4.6 4.7 4.8 4.9 Figure. 6 5.1 5.2 5.3 5.4 5.5 Figure. 7 IGND vs VIN (ILOAD=1A) IGND vs ILOAD (VIN = 5.1V) 0.500 0.500 0.450 0.400 IGND - mA 0.400 IGND - mA 5.0 VIN - V 0.350 0.300 0.300 0.200 0.100 0.250 0.000 0.001 0.200 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 Figure. 8 © 2001 Microchip Technology Inc. DS21558A 0.01 0.1 1 10 100 1000 ILOAD - mA VIN - V Figure. 9 7 TC3827-2 12/12/00 Lithium-Ion Battery Charger TYPICAL CURVES (CONT.) TC3827 IGND vs Temperature (VIN = 5.1V, ILOAD = 10mA) 4.0 0.450 0.400 3.5 0.350 3.0 0.300 2.5 VOUT - V IGND - mA Power-Up/Power-Down (ILOAD=10mA) 4.5 0.500 0.250 0.200 0.150 2.0 1.5 1.0 0.100 0.5 0.050 0.0 0.000 -20.0 0.0 20.0 40.0 60.0 0.0 80.0 1.0 2.0 3.0 4.0 5.0 4.0 3.0 2.0 1.0 0.0 VIN - V TEMPERATURE - °C Figure. 11 Figure. 10 Current Limit Foldback (VIN = 5.1V, RSENSE=0.5Ohms) VOUT vs Temperature (VIN = 5.1V, ILOAD = 10mA) 5.000 4.220 4.000 4.180 VOUT - V 3.000 VOUT - V VOUT= 4.200 4.160 2.000 4.140 1.000 4.120 VOUT 4.100 0.000 0 20 40 60 80 100 120 4.080 -20.0 ILOAD -mA 0.0 20.0 40.0 60.0 80.0 TEMPERATURE - °C Figure. 13 Figure. 12 VOUT - V VOUT - V Line Transient Response (10µF Output Cap) 5.5 4.5 4.2 4.1 4.0 Figure. 14 TC3827-2 12/12/00 8 © 2001 Microchip Technology Inc. DS21558A Lithium-Ion Battery Charger TC3827 TAPING FORM Component Taping Orientation for 8-Pin MSOP Devices User Direction of Feed User Direction of Feed PIN 1 W PIN 1 Standard Reel Component Orientation for TR Suffix Device P Reverse Reel Component Orientation for RT Suffix Device Carrier Tape, Number of Components Per Reel and Reel Size Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size 12 mm 8 mm 2500 13 in 8-Pin MSOP PACKAGE DIMENSIONS 8-Pin MSOP PIN 1 .122 (3.10) .114 (2.90) .197 (5.00) .187 (4.80) .026 (0.65) TYP. .122 (3.10) .114 (2.90) .043 (1.10) MAX. .016 (0.40) .010 (0.25) © 2001 Microchip Technology Inc. DS21558A .008 (0.20) .005 (0.13) 6° MAX. .006 (0.15) .002 (0.05) .028 (0.70) .016 (0.40) 9 Dimensions: inches (mm) Printed in the12/12/00 U.S.A. TC3827-2 Lithium-Ion Battery Charger TC3827 WORLDWIDE SALES AND SERVICE AMERICAS New York Corporate Office 150 Motor Parkway, Suite 202 Hauppauge, NY 11788 Tel: 631-273-5305 Fax: 631-273-5335 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: 480-792-7627 Web Address: http://www.microchip.com Rocky Mountain 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7966 Fax: 480-792-7456 ASIA/PACIFIC (continued) San Jose Microchip Technology Inc. 2107 North First Street, Suite 590 San Jose, CA 95131 Tel: 408-436-7950 Fax: 408-436-7955 Singapore Microchip Technology Singapore Pte Ltd. 200 Middle Road #07-02 Prime Centre Singapore, 188980 Tel: 65-334-8870 Fax: 65-334-8850 Taiwan Atlanta 6285 Northam Drive, Suite 108 Mississauga, Ontario L4V 1X5, Canada Tel: 905-673-0699 Fax: 905-673-6509 500 Sugar Mill Road, Suite 200B Atlanta, GA 30350 Tel: 770-640-0034 Fax: 770-640-0307 Microchip Technology Taiwan 11F-3, No. 207 Tung Hua North Road Taipei, 105, Taiwan Tel: 886-2-2717-7175 Fax: 886-2-2545-0139 ASIA/PACIFIC Austin EUROPE China - Beijing Australia Analog Product Sales 8303 MoPac Expressway North Suite A-201 Austin, TX 78759 Tel: 512-345-2030 Fax: 512-345-6085 Boston 2 Lan Drive, Suite 120 Westford, MA 01886 Tel: 978-692-3848 Fax: 978-692-3821 Boston Analog Product Sales Unit A-8-1 Millbrook Tarry Condominium 97 Lowell Road Concord, MA 01742 Tel: 978-371-6400 Fax: 978-371-0050 Toronto Microchip Technology Beijing Office Unit 915 New China Hong Kong Manhattan Bldg. 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No licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellectual property rights. The Microchip logo and name are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries. All rights reserved. All other trademarks mentioned herein are the property of their respective companies. TC3827-2 12/12/00 10 © 2001 Microchip Technology Inc. DS21558A