www.fairchildsemi.com FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect Features General Description • • • • • • • • • • • • The FAN4855 is a low power boost regulator designed for low voltage DC to DC conversion in 2-cell battery powered systems such as digital cameras, cell phones and PDAs. The converter starts-up at 1.3V and operates after the start at an input voltage as low as 1V. Output voltage can be adjusted by external resistors from 3.3V to 5V with a maximum load current of 0.5A. Quiescent current in shut-down mode is less than 10µA, which maximizes the battery live time. The ON time changes with the input voltage to maintain the ripple current constant and to provide the highest efficiency over a wide load range—while maintaining low peak currents in the boost inductor. The combination of built-in power transistors, synchronous rectification and low supply current, make the FAN4855 ideal for portable applications. The FAN4855 is available in 8-lead MSOP and TSSOP packages. Low power PFM boost regulator Input voltage range is from 1.6V to 4.5V Output voltage range is from 3V to 5V 500mA maximum load current capability 95% efficient power conversion 2-3 cell and single cell Li-Ion systems Variable on-time Pulse Frequency Modulation (PFM) Internal synchronous rectifier (no need for external diode) Low-battery detection Logic controlled shutdown with true-load disconnect Low (80µA) quiescent current MSOP-8 and TSSOP-8 Packages Applications • • • • • • DSCs PDAs Cell phones, smart phones Portable instrumentations 2-3 AA / AAA cells operated devices Single cell Li-Ion operated devices Typical Application Input 1.6V to 4.5V FAN4855 1 VIN On Off Low Battery Detect In Low Battery Detect Out 2 SHDN GND 8 VL 7 3 LBI VOUT 6 4 LB0 FB 5 Output 3.3V to 5V up to 0.5A REV. 1.0.0 3/17/04 PRODUCT SPECIFICATION FAN4855 Pin Configuration 8-Pin TSSOP and MSOP VIN 1 8 GND SHDN LBI 2 7 VL 3 6 VOUT LB0 4 5 FB TOP VIEW Pin Description PIN NAME FUNCTION 1 VIN Battery Input Voltage. Supplies the IC during start-up. After the output is running, the IC draws power from VOUT. 2 SHDN Shut Down. Pulling this pin low shuts down the regulator, isolating the load from the input. 3 LBI Low-Battery Input. Pulling this pin below 0.39V causes the LBO pin to go low. 4 LBO Low-Battery Output. This pin provides an active low signal to alert the user when the LBI voltage falls below its targeted value. The open-drain output can be used to reset a microcontroller. 5 FB 6 VOUT 7 VL 8 GND Feedback Input. For setting the output voltage. Connect this pin to the resistor divider. Boost regulator output. Output voltage can be set to be in the 3 to 5V range. Startup at moderate load is achievable at input voltages around 1.35V. Boost inductor connection. Connect an inductor between this pin and VIN. When servicing the output supply, this pin pulls low, charging the inductor, then shuts off dumping the energy through the synchronous rectifier to the output. Ground of the IC. Absolute Maximum Ratings Absolute Maximum Ratings are those values, beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. Parameter Min. Max. Units VIN, VOUT Voltages (Relative to GND) -0.3 6.5 V Switch Voltage (VL to GND) -0.3 VOUT + 0.3 V Voltage on any other Pin -0.3 VOUT + 0.3 V Peak Switch Current (Ipeak) — Internally Limited — Output Current (IOUT) Continuous Power Dissipation Thermal Resistance (θJA) 500 mA TSSOP Package 525 mW MSOP Package 315 TSSOP Package 124 MSOP Package 206 Junction Temperature Storage Temperature Range Lead Temperature (soldering, 10s) 2 -65 °C/W 150 °C 150 °C 300 °C REV. 1.0.0 3/17/04 FAN4855 PRODUCT SPECIFICATION Recommended Operating Conditions Parameter Min. Max. Units Temperature Range VIN Operating Range -40 +85 °C 1.6 0.9 VOUT V VOUT Operating Range 3.0 5.0 V Electrical Characteristics Unless otherwise specified, VIN = 1.6V to 3V, ILOAD = 1mA, TA = -40°C to +85°C. Test Circuit Fig.1. Typical values are at TA = +25°C Parameter Typ. Max. Units Start Up Voltage ILOAD < 1mA Conditions 1.35 1.6 V Operating Voltage After start ILOAD =10mA, VOUT = 3.3V or 5V 1.0 Output Voltage VOUT(nom.) = 3.3V (Note 1) VOUT(nom.) = 5V Output Voltage Adjust Range Steady State Output Current Pulse Width 3.15 4.775 3.3 5 3 V 3.45 5.225 5 V V V VOUT = 3.3V, VIN = 2.5V 300 500 mA VOUT = 5V, VIN = 2.5V 200 330 mA VIN = 3V 0.8 1.4 2 µs VIN = 2.4V 1.2 1.7 2.5 µs VIN = 1.8V 1.6 2.2 3.3 µs VIN = 1.6V 1.7 2.5 4.0 µs Minimum Off-Time Line Regulation Min. µs 1 IOUT = 2mA, VOUT = 3.3V 0.5 2 % VOUT = 5V 0.5 2 % 0 to 250mA, VIN = 2.4V, VOUT = 3.3V 0.5 % 1 % Feedback Voltage (VFB) 1.243 V LBI Threshold Voltage 0.390 V 25 mV Load Regulation 0 to 150mA, VIN = 2.4V, VOUT = 5V LBI Hysteresys 0.35 Ω Power Efficiency ILOAD = 200mA, VIN = 3V, VOUT = 3.3V 95 % Input Current in Shut Down Mode SHDN = 0V, VIN = 3V (Note 2) 8 50 µA Quiescent Current SHDN = 3V, VIN = 3V, VOUT = 3.3V (Note 2) 80 160 µA LBO Output Voltage Low VLBI = 0, ISINK = 1mA 0.2 V SHDN Input Threshold Voltage VIN = 3V, VOUT = 3.3V/5V 1.5 V SHDN Input Threshold Voltage VIN = 1.6V, VOUT = 3.3V/5V 0.8 V Internal NFET, PFET ON Resist. ILOAD = 100mA Notes: 1. R4, R5, R6 tolerance ≤ 0.1%. 2. Current through R1, R2 is not taken into account. REV. 1.0.0 3/17/04 3 PRODUCT SPECIFICATION VIN 2 1 1.6V to 3.0V FAN4855 10uH R1 750K SHDN 2 1 JP2 U1 FAN4855 1 Vin 8 Gnd 2 SHDN JP3 Reset 2 1 3 LBI 4 + C1 47µF R2 240K LBO VL Vout FB 7 J1 SCOPE JACK 6 5 C3 18pF R4 402K VOUT R3 100K 1 2 JP1 3.3V or 5V Ext Pull Up 2 1 R6 287K R5 240K + C2 47µF C5 0.1µF GND1 1 2 GND 2 1 Figure 1. Test Circuit 4 REV. 1.0.0 3/17/04 FAN4855 PRODUCT SPECIFICATION Typical Operating Characteristics (L = 10µH, CIN = 47µF, COUT = 47µF/1.0µF, T = 25°C) Load Current vs. Start-Up Voltage (Resistive Load) 100.0 600 90.0 500 400 VOUT = 5V 300 200 Vin=2.0V 70.0 Efficiency, % Load Current, mA Vin=3V 80.0 VOUT = 3.3V 50.0 40.0 30.0 20.0 10.0 2 2.5 3 3.5 0.0 0.1 4 1 Input Voltage, V Efficiency vs. Load Current Vout = 5V 100.0 90.0 SHDN Threshold Voltage SHDN Voltage, V Efficiency, % Vin=2.0V Vin=1.5V 60.0 50.0 40.0 30.0 1.9 1.7 1.5 1.3 1.1 20.0 0.9 10.0 0.7 0.0 0.1 1 10 100 0.5 1.5 1000 2 2.5 3 3.5 4 Output Current, mA Input Voltage, V Starting Up and Turning Off VOUT = 3.3V, Iloads = 10mA to 50mA Starting Up and Turning Off VOUT = 5V, Iloads = 10mA to 50mA 4.5 5 3.5 START UP 3 TURN OFF: Iload=50mA 2.5 Output Voltage, V Output Voltage, V 1000 2.1 70.0 START UP Iload=10mA 2 1.5 1 4 3 Iload=50mA Iload=10mA Iload=10mA to 50mA 2 TURN OFF: 1 0.5 0 0.6 10 100 Output Current, mA 2.3 Vin=3V 80.0 4 Vin=1.5V 60.0 100 0 1.5 Efficiency vs. Load Current Vout = 3.3V 0.8 REV. 1.0.0 3/17/04 1.0 1.2 1.4 Input Voltage, V 1.6 1.8 0 0.6 0.8 1.0 1.2 1.4 Input Voltage, V 1.6 1.8 5 PRODUCT SPECIFICATION FAN4855 Typical Operating Characteristics (L = 10µH, CIN = 47µF, COUT = 47µF/1.0µF, T = 25°C) No Load Supply Current vs. Input Voltage Output Voltage vs. Temperature 0.2 VOUT = 5V Input Current (µA) “ON” 100 VOUT = 3.3V 10 “OFF” 1 0.1 6 VOUT Relative Change (%) 1000 0 1 2 3 Input Voltage (V) 4 5 0 -0.2 -0.4 -0.6 -50 -25 0 25 50 75 100 Temperature (°C) REV. 1.0.0 3/17/04 PRODUCT SPECIFICATION FAN4855 Typical Operating Characteristics (Continued) Line Transient Response @100mA Load Exiting Shutdown VOUT VSHDN Load Transient Response Heavy-Load Switching Waveforms Load Transient Response Inductor Current and Switching Node Voltage VL Inductor Current IL VOUT 7 VL REV. 1.0.0 3/17/04 PRODUCT SPECIFICATION FAN4855 Block Diagram LBO VL 4 7 SHDN Control Logic LBI 2 – 3 A3 0.39V + SHDN ILIMIT VOUT VIN 1 Q2 Synchronous Rectifier Control Start-Up VOUT + 6 A2 – Minimum Off-Time Logic Current Limit Control ILIMIT VFB 5 Variable On-Time One Shot Q1 N ILIMIT SHDN 1 – A1 + VREF 8 GND Functional Description Boost Regulator FAN4855 is an adjustable boost regulator that combines variable ON and minimum OFF architecture with synchronous rectification. Unique control circuitry provides highefficiency power conversion for both light and heavy loads by transitioning between discontinuous and continuous conduction mode based on load conditions. There is no oscillator; a constant-peak-current limit of 0.8A in the inductor allows the inductor current to vary between this peak limit and some lesser value. The switching frequency depends upon the load, the input and output voltage ranging up to 430kHz. The input voltage VIN comes to VIN pin and through the external inductor to the VL pin of the device. The loop from VOUT closes through the external resistive voltage divider to the feedback pin VFB. The transfer ratio of this divider determines the output voltage. When VFB voltage drops below the VREF = 1.24V the error amplifier A1 signals to regulator to deliver charge to the output by triggering the Variable OnTime One Shot. One Shot generates a pulse at the gate of the Power NMOS transistor Q1. This transistor will charge the Inductor L1 for the time interval TON resulting in a peak current given by: T ON × V IN I L ( PEAK ) = -------------------------L1 8 When the one–shot times out, the Q1 transistor releases the VL pin, allowing the inductor to fly-back and momentarly charge the output through the body diode of the transistor Q2. But, as the voltage across the Q2 changes polarity, its gate will be driven low by the Synchronous Rectifier Control Circuit (SRC), causing Q2 to short out its body diode. The inductor then delivers the charge to the load by discharging into it through Q2. Under light load conditions, the amount of energy delivered in this single pulse satisfies the voltage-control loop, and the converter does not command any more energy pulses until the output drops again below the lower-voltage threshold. Under medium and heavy loads, a single energy pulse is not sufficient to force the output voltage above its upper threshold before the minimum off time has expired and a second charge cycle is commanded. Since the inductor current has not reached zero in this case, the peak current is greater than the previous value at the end of the second cycle. The result is a ratcheting of inductor current until either the output voltage is satisfied, or the converter reaches its set current limit. After a period of time TOFF > 1µS, determined by Minimum Off–Time Logic and if VOUT is low (VFB < VREF), the Variable On-Time One Shot will be turned ON again and the process repeats. The output capacitor of the converter filters the variable component, limiting the output voltage ripple to a value determined by its capacitance and its ESR. REV. 1.0.0 3/17/04 FAN4855 PRODUCT SPECIFICATION The synchronous rectifier significantly improves efficiency without the addition of an external component, so that conversion efficiency can be as high as 94% over a large load range, as shown in the Typical Operating Characteristics. Even at light loads, the efficiency stays high because the switching losses of the converter are minimized by reducing the switching frequency. The battery voltage, at which the detection circuit switches, can be programmed with a resistive divider connected to the LBI-pin. The resistive divider scales down the battery voltage to a voltage level of tenths of volt, which is then compared to the LBI threshold voltage. The LBI-pin has a built-in hysteresis of 25 mV. The resistor values R1 and R2 can be calculated using the following equation: Error Detection Comparator (LBI – LBO) VIN_MIN = 0.39 x (R1+R2)/R2 An additional comparator A3 is provided to detect low VIN or any other error conditions that is important to the user. The non-inverting input of the comparator is internally connected to a reference threshold voltage Vth while the inverting input is connected to the LBI pin. The output of the low battery comparator is a simple open-drain output that goes active low if the battery voltage drops below the programmed threshold voltage on LBI. The output requires a pull-up resistor having a recommended value of 100 kΩ, should be connected only to VOUT. The low-battery detector circuit is typically used to supervise the battery voltage and to generate an error flag or a RESET command when the battery voltage drops below a user-set threshold voltage. The function is active only when the device is enabled. When the device is disabled, the LBO-pin is high impedance. Shutdown The device enters shutdown when VSHDN is approximately less than 0.5VIN. During shutdown the regulator stops switching, all internal control circuitry including the lowbattery comparator is switched off and the load is disconnected from the input. The output voltage may drop below the input voltage during shutdown. The typical dependence shutdown voltage versus input voltage and the timing process of the exiting shutdown are shown on the Diagrams. For normal operation VSHDN should be driven up 0.8VIN or connected to the VIN. Application Information Selecting the Output Voltage The output voltage VOUT can be adjusted from 3V to 5V, choosing resistors R4 and R5 of the divider in the feedback circuit (see Test Circuit). The value of the R5 is recommended to be less than 270k. R4 can be calculated using the following equation: R4 = R5[(VOUT/VREF) – 1] where VREF = 1.24V Setting the LBI Threshold of Low-Battery Detector Circuit The value of R2 should be 270k or less to minimize bias current errors. R1 is then found by rearranging the equation: R1 = R2 x (VIN_MIN/0.39 – 1) If the low-battery detection circuit is not used, the LBI-pin should be connected to GND (or to VIN) and the LBO-pin can be left unconnected or tied to GND. Do not let the LBI-pin float. Component Selection Input and Output Capacitors Selection For common general purpose applications, 47µF tantalum capacitors are recommended. Ceramic capacitors are recommended at input only; if connected at the output they cannot improve significantly the voltage ripple. More effective in reducing the output ripple at light load is to connect a small capacitor of 18 to 100pF between VOUT and FB pin. Table 1. Recommended capacitors Vendor MuRata AVX Sprague Kemet Description X5R Ceramic TAJ,TPS series tantalum 595D series tantalum T494 series tantalum Inductor Selection The inductor parameters directly influencing the device performance are the saturation current and the DC resistance. The FAN4855 operates with a typical inductance of 10µH. The lower the resistance, the higher the efficiency. The saturation current should be rated higher than 0.8A, which is the typical threshold to switch off the N-channel power FET. Table 2. Recommended Inductors Supplier MuRata Coilcraft Coiltronics Sumida Manufacturer Part Number LQ66C100M4 DT1608C-103 UP1B100 CDR63B-100 The LBO-pin goes active low when the voltage on the LBI-pin decreases below the set threshold typical voltage of 390 mV, which is set by to the internal reference voltage. REV. 1.0.0 3/17/04 9 PRODUCT SPECIFICATION Careful design of printed circuit board is recommended since high frequency switching and high peak currents are present in DC/DC converters applications. A general rule is to place the converter circuitry well away from any sensitive analog components. The printed circuit board layout should be based on some simple rules to minimize EMI and to ensure good regulation performances: 1. Place the IC, inductor, input and output capacitor as close together as possible. 2. Keep the output capacitor as close to the FAN4855 as possible with very short traces to VOUT and GND pins. Typically it should be within 0.25 inches or 6 mm. 3. Keep the traces for the power components wide, typically > 50 mils or 1.25 mm. 4. Place the external networks for LBI and FB close to FAN4855, but away from the power components as far as possible to prevent voltage transient from coupling into sensitive nodes. 5. On multilayer boards use component side copper for grounding around the IC and connect back to a quiet ground plane using vias. The ground planes act as electromagnetic shields for some of the RF energy radiated. 6. 10 Application Example The FAN4855 can be used as a constant current source to drive white LEDs like QTLP670C-IW. As shown in the diagram below, the current is maintained constant over a wide range of input voltages. L = 10µH D1 62Ω FAN4855 1 2 3 4 + + Cin 10µF 8 7 6 5 + D2 D3 Cout 10µF D4 LED Current (mA) Layout and Grounding Considerations FAN4855 62Ω 62Ω 62Ω 20 19.8 19.6 19.4 19.2 19 18.8 18.6 18.4 18.2 18 0 1 2 3 4 5 Input Voltage (V) The connection of the GND pin of the IC (pin 8) to the overall grounding system should be directly to the bottom of the output filter capacitor. A star grounding system radiating from where the power enters the PCB, is a recommended practice. REV. 1.0.0 3/17/04 PRODUCT SPECIFICATION FAN4855 Mechanical Dimensions Package: T08, 8-Pin TSSOP 0.113 - 0.123 (2.87 - 3.12) 8 0.169 - 0.177 0.246 - 0.258 (4.29 - 4.50) (6.25 - 6.55) PIN 1 ID 1 0.026 BSC (0.65 BSC) 0.043 MAX (1.10 MAX) 0°-8° 0.033 - 0.037 (0.84 - 0.94) 0.008 - 0.012 (0.20 - 0.30) 0.002 - 0.006 (0.05 - 0.71) 0.020 - 0.028 (0.51 - 0.71) 0.004 - 0.008 (0.10 - 0.20) SEATING PLANE 11 REV. 1.0.0 3/17/04 FAN4855 PRODUCT SPECIFICATION Mechanical Dimensions Package: 8-Pin MSOP 0.118 ± 0.004 [3 ± 0.1] -A8 5 SYMM C L 0.118±0.004 [3±0.1] -B- 0.193±0.004 [4.9±0.1] 0.189 [4.8] 0.040 [1.02] TYP PIN 1 IDENT 0.016 [0.41] TYP 1 0.0256 [0.65] TYP 4 (0.0256) TYP [0.65] 0.030 - 0.037 [0.76 - 0.94] LAND PATTERN RECOMMENDATION R 0.005 TYP [0.13] 0.005 R TYP [0.13] GAGE PLANE (0.010) [0.25] D _ C_ 0.002[0.05] C 0.002 - 0.006 TYP [0.06 - 0.15] 0.012+0.002 TYP [0.3 ± 0.05] 0.002[0.05] M A S 0.034 [0.84] E S 0.021±0.005 [0.53±0.12] 0.375 [0.953] 0°-6° TYP SEATING PLANE 0.007±0.002 [0.18±0.05] TYP REV. 1.0.0 3/17/04 12 PRODUCT SPECIFICATION FAN4855 Ordering Information (TA = -40°C to +85°C) Part Number Package Packing FAN4855MTC 8 Pin TSSOP Rails FAN4855MTCX 8 Pin TSSOP Tape and Reel FAN4855MU 8 Pin MSOP Rails FAN4855MUX 8 Pin MSOP Tape and Reel DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 3/17/04 0.0m 005 Stock#DS30004855 2004 Fairchild Semiconductor Corporation