FAN5308 800mA High-Efficiency Step-Down DC-DC Converter Features Description ■ 96% efficiency, synchronous operation Designed for use in battery-powered applications, the FAN5308 is a high-efficiency, low-noise synchronous PWM current mode and pulse skip (power-save) mode DC-DC converter. It can provide up to 800mA of output current over an input range from 2.5V to 5.5V. The output voltage can be externally adjusted over a range of 0.8V to 5.5V by means of an external voltage divider. ■ Adjustable output voltage options from 0.8V to VIN ■ 2.5V to 5.5V input voltage range ■ Up to 800mA output current ■ Fixed-frequency 1.3MHz PWM operation ■ High-efficiency, power-save mode ■ 100% duty cycle low-dropout operation tm At moderate and light loads, pulse skipping modulation is used. Dynamic voltage positioning is applied and the output voltage is shifted 0.8% above nominal value for increased headroom during load transients. At higher loads, the system automatically switches over to current mode PWM control, operating at 1.3MHz. A current mode control loop with fast transient response ensures excellent line and load regulation. To achieve high efficiency and ensure long battery life, the quiescent current is reduced to 25µA in power-save mode, and the supply current drops below 1µA in shut-down mode. The FAN5308 is available in a 3x3mm 6-lead MLP package. ■ Soft-start ■ Output over-voltage protection ■ Dynamic output voltage positioning ■ 25µA quiescent current ■ Thermal shutdown and short-circuit protection ■ Pb-free 3x3mm 6-lead MLP package Applications ■ Pocket PCs, PDAs ■ Cell phones ■ Battery-powered portable devices ■ Digital cameras ■ Hard disk drives ■ Set-top boxes ■ Point-of-load power ■ Notebook computers ■ Communications equipment Ordering Information Product Number Output Voltage Package Type Order Code FAN5308 Adjustable 3x3mm 6-Lead MLP FAN5308MPX Typical Application VIN CIN PGND SW 1 2 10μF EN 3 6 P1 (AGND) 5 4 VOUT 1.2V (800mA) 3.3μH NC R1 5KΩ R2 10KΩ FB COUT 2 x 10μF Figure 1. Typical Application © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter June 2007 VIN 1 PGND 2 EN 3 P1 (AGND) 6 SW 5 NC 4 FB Figure 2. Pin Assignment for 3x3mm 6-Lead MLP Pin Description Pin # Name P1 AGND 1 VIN 2 PGND 3 EN Enable Input. Logic high enables the chip and logic low disables the chip, reducing the supply current to less than 1µA. Do not float this pin. 4 FB Feedback Input. Adjustable voltage option, connect this pin to the resistor divider. 5 NC No Connection Pin. 6 SW Switching Node. This pin is connected to the internal MOSFET switches. © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 Description Analog Ground. P1 must be soldered to the PCB ground. Supply Voltage Input. Power Ground. This pin is connected to the internal MOSFET switches. This pin must be externally connected to AGND. www.fairchildsemi.com 2 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Pin Configuration Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Parameter Min. Max. Unit VIN -0.3 7.0 V Voltage On Any Other Pin -0.3 VIN V 260 °C Lead Soldering Temperature (10 seconds) Junction Temperature Storage Temperature -65 Thermal Resistance, Junction-to-Case (θJC), 3x3mm 6-lead MLP(1) Electrostatic Discharge Protection (ESD) Level(2) HBM 4 CDM 1 150 °C 150 °C 8 °C/W kV Notes: 1. Junction-to-ambient thermal resistance, θJA, is a strong function of PCB material, board thickness, thickness and number of copper planes, number of via used, diameter of via used, available copper surface, and attached heat sink characteristics. 2. Using Mil Std. 883E, method 3015.7 (Human Body Model) and EIA/JESD22C101-A (Charged Device Model). Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings. Parameter Min. Supply Voltage Range 2.5 Output Voltage Range, Adjustable Version 0.8 Typ. Output Current Inductor(3) Input Capacitor (3) Output Capacitor (3) Max. Unit 5.5 V VIN V 800 mA 3.3 µH 10 µF 2 x 10 µF Operating Ambient Temperature Range -40 +85 °C Operating Junction Temperature Range -40 +125 °C Note: 3. Refer to the Applications section for details. © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 3 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Absolute Maximum Ratings VIN = VOUT + 0.6V (minimum 2.5V) to 5.5V, IOUT = 350mA, VOUT =1.2V, EN = VIN, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Symbol VIN Parameter Input Voltage Conditions 0 mA ≤ IOUT ≤ 800 mA Min. IOUT = 0mA, Device is not switching IQ Quiescent Current IOUT = 0mA, Device is switching(4) Shutdown Supply Current EN = GND VUVLO Under-Voltage Lockout Threshold VIN Rising VENH Enable High Input Voltage VENL Enable Low Input Voltage ISD IEN EN Input Bias Current PMOS On Resistance RDS-ON NMOS On Resistance ILIM P-channel Current Limit fOSC Oscillator Frequency Ilkg_(N) Ilkg_(P) VREF tST Typ. 2.5 20 Max. Units 5.5 V 35 µA R2 =10kΩ 50 µA R2 =100kΩ 25 µA 1.9 Hysteresis 0.1 1.0 µA 2.1 2.3 V 150 mV 1.3 V 0.4 V µA EN = VIN or GND 0.01 0.10 VIN = VGS = 5.5V 250 350 VIN = VGS = 2.5V 300 400 VIN = VGS = 5.5V 200 300 VIN = VGS = 2.5V 250 350 1300 1500 2000 mA 1000 1300 1500 KHz 0.1 1 µA 0.1 1 µA 2.5V < VIN < 5.5V N-Channel Leakage Current VDS = 5.5V P-Channel Leakage Current VDS = 5.5V mΩ mΩ Line Regulation IOUT = 10mA 0.16 %/V Load Regulation 350mA ≤ IOUT ≤ 800mA 0.15 % 0.8 V Reference Voltage Output DC Voltage Accuracy(5) 0mA ≤ IOUT ≤ 800mA Over-Temperature Protection PWM Mode Only 350mA ≤ IOUT ≤ 800mA Start-Up Time IOUT = 800mA, COUT = 20µF -3 +3 % Rising Temperature 150 °C Hysteresis 20 °C 800 µs Notes: 4. Refer to the Application section for details. 5. For output voltages ≤ 1.2V, a 40µF output capacitor value is required to achieve a maximum output accuracy of 3% while operating in power-save mode (PFM mode). © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 4 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Electrical Characteristics TA = 25°C, CIN = 10µF, COUT = 20µF, L = 3.3µH, R2 = 10kΩ, unless otherwise noted. 100 95 Efficiency (%) Efficiency (%) 90 85 VIN = 5V 80 V OUT = 3.3V VIN = 3.6V 75 VIN = 3.6V V OUT = 3V VOUT = 1.2V 70 65 60 1 10 100 1000 100 95 90 85 80 75 70 65 60 VIN = 5.5V 55 50 45 40 35 0.1 1 V OUT = 3.3V VIN = 3.9V 10 Load Current (mA) 100 1000 Load Current (mA) Figure 3. Efficiency vs. Load Current Figure 4. Efficiency vs. Load Current 100 1.214 V OUT = 1.2V 1.212 R 2 = 100kΩ 1.210 90 Output Voltage (V) 80 Efficiency (%) R 2 = 100kΩ 70 V IN = 5.5V 60 VIN = 2.5V 50 V IN = 3. 6V 40 VIN = 5V 1.208 1.206 1.204 1.202 1.200 1.198 1.196 1.194 30 0.1 1 10 100 1.192 1000 0 200 400 Load Current (mA) Figure 5. Efficiency vs. Load Current 1000 1400 Oscillator Frequency (kHz) V OUT = 1. 2V 70 Quiescent Current (μA) 800 Figure 6. Output Voltage vs. Load Current 80 60 50 40 600 Load Current (mA) R 2 = 10kΩ 30 20 10 0 2.5 R 2 = 100kΩ 3.0 3.5 4.0 4.5 5.0 1360 1340 VIN = 5.5V 1320 1300 1280 V IN = 3.6V 1260 1240 1220 VIN = 2.5V 1200 -40 5.5 -20 0 20 40 60 80 100 Temperature (°C) Input Voltage (V) Figure 8. Frequency vs. Temperature Figure 7. Quiescent Current vs. Input Voltage © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 1380 www.fairchildsemi.com 5 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Typical Performance Characteristics Inductor Current (200mA/div) Output SW Node Voltage Voltage (20mV/div) (2V/div) SW Node Voltage (2V/div) Inductor Output Current Voltage (200mA/div) (5mV/div) Time (1μs/div) 600mA 100mA Time (5μs/div) Figure 10. Power-Save Mode Inductor Load Current Current Step (500mA/div) Inductor Load Current Output Current Step Voltage (50mV/div) (500mA/div) Figure 9. PWM Mode VOUT = 1.2V Output Voltage (50mV/div) VOUT = 1.2V 100mA 600mA Time (10μs/div) Time (10μs/div) Figure 11. Load Transient Response Inductor Output Voltage at Current Voltage Enable Pin (400mA/div) (5V/Div) (500mV/div) Inductor Output Current Voltage (500mV/div) (200mA/div) Voltage at Enable Pin (5V/Div) Figure 12. Load Transient Response VOUT = 1.2V IOUT = 10mA Time (200μs/div) Time (100μs/div) Figure 13. Start-Up Response © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 VOUT = 1.2V IOUT = 800mA Figure 14. Start-Up Response www.fairchildsemi.com 6 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Typical Performance Characteristics (Continued) TA = 25°C, CIN = 10µF, COUT = 20µF, L = 3.3µH, R2 = 10kΩ, unless otherwise noted. FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Block Diagram VIN EN DIGITAL SOFT START UNDER-VOLTAGE LOCKOUT IS REF PFM COMP IS CURRENT SENSE FB ERROR AMP LOGIC CONTROL COMP MOSFET SW DRIVER 0.8V GND IS OVERVOLTAGE COMP OSC SLOPE COMPENSATION REF FB NEG. LIMIT COMP NEG. LIMIT SENSE GND Figure 15. Block Diagram Detailed Operation Description PFM (Power-Save) Mode The FAN5308 is a step-down converter operating in a current-mode PFM/PWM architecture with a typical switching frequency of 1.3MHz. At moderate to heavy loads, the converter operates in pulse-width-modulation (PWM) mode. At light loads, the converter enters a power-save mode (PFM pulse skipping) to keep the efficiency high. As the load current decreases and the inductor current reaches negative value, the converter enters pulse-frequency-modulation (PFM) mode. The transition point for the PFM mode is given by the equation: 1 – ( V OUT ⁄ V IN ) I OUT = V OUT × -------------------------------------------2×L×f PWM Mode The typical output current, when the device enters PFM mode, is 150mA for input voltage of 3.6V and output voltage of 1.2V. In PFM mode, the device operates with a variable frequency and constant peak current, thus reducing the quiescent current to minimum. Consequently, the high efficiency is maintained at light loads. As soon as the output voltage falls below a threshold, set at 0.8% above the nominal value, the P-channel transistor is turned on and the inductor current ramps up. The P-channel switch turns off and the N-channel turns on as the peak inductor current is reached (typical 450mA). In PWM mode, the device operates at a fixed frequency of 1.3MHz. At the beginning of each clock cycle, the Pchannel transistor is turned on. The inductor current ramps up and is monitored via an internal circuit. The Pchannel switch is turned off when the sensed current causes the PWM comparator to trip when the output voltage is in regulation or when the inductor current reaches the current limit (set internally to typically 1500mA). After a minimum dead time, the N-channel transistor is turned on and the inductor current ramps down. As the clock cycle is completed, the N-channel switch is turned off and the next clock cycle starts. ©2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 EQ. 1 www.fairchildsemi.com 7 The reference and the circuit remain reset until the VIN crosses its UVLO threshold. The FAN5308 has an internal soft-start circuit that limits the inrush current during start-up. This prevents possible voltage drops of the input voltage and eliminates the output voltage overshoot. The soft-start is implemented as a digital circuit, increasing the switch current in four steps to the P-channel current limit (1500mA). Typical start-up time for a 20µF output capacitor and a load current of 800mA is 800µs. Short-Circuit Protection The switch peak current is limited cycle-by-cycle to a typical value of 1500mA. In the event of an output voltage short circuit, the device operates with a frequency of 400kHz and minimum duty cycle; therefore, the average input current is typically 200mA. 100% Duty Cycle Operation As the input voltage approaches the output voltage and the duty cycle exceeds the typical 95%, the converter turns the P-channel transistor continuously on. In this mode, the output voltage is equal to the input voltage, minus the voltage drop across the P-channel transistor: VOUT = VIN – ILOAD × (RdsON + RL) Thermal Shutdown When the die temperature exceeds 150°C, a reset occurs and remains in effect until the die cools to 130°C. At that time, the circuit is allowed to restart. EQ. 2 where: RdsON = P-channel switch on resistance ILOAD = Output current RL = Inductor DC resistance ©2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 8 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter UVLO and Soft Start The N-channel transistor is turned off before the inductor current becomes negative. At this time, the P-channel is switched on again, starting the next pulse. The converter continues these pulses until the high threshold (typical 1.6% above nominal value) is reached. A higher output voltage in PFM mode gives additional headroom for the voltage drop during a load transient from light to full load. The voltage overshoot during this load transient is also minimized due to active regulation during turn on of the N-channel rectifier switch. The device stays in sleep mode until the output voltage falls below the low threshold. The FAN5308 enters the PWM mode as soon as the output voltage can no longer be regulated in PFM with constant peak current. Setting the Output Voltage Capacitors Selection The internal reference is 0.8V (typical). The output voltage is divided by a resistor divider, R1 and R2 to the FB pin. The output voltage is given by: For best performances, a low-ESR input capacitor is required. A ceramic capacitor of at least 10µF, placed close to the VIN and AGND pins, is recommended. The output capacitor determines the output ripple and the transient response. R1 V OUT = V REF × 1 + -------- R2 EQ. 3 Capacitor Value where R1 + R2 < 800KΩ. According to this equation, and assuming desired output voltage of 1.5096V, and given R2 = 10kΩ, the calculated value of R1 is 8.87kΩ. If quiescent current is a key design parameter, a higher value feedback resistor can be used (e.g. R2 = 100kΩ) and a small bypass capacitor of 10pF is required in parallel with the upper resistor, as shown in Figure 16. VIN CIN PGND SW 1 2 10µF EN 6 P1 (AGND) 3 NC 5 R1 FB 4 R2 Taiyo Yuden JMK212BJ106MG TDK C2012X5ROJ106K Murata JMK316BJ106KL GRM32ER61C106K Table 2: Recommended Capacitors PCB Layout Recommendations COUT 2 x 10µF 5KΩ Part Number C3216X5ROJ106M VOUT 1.2V (800mA) Cf 3.3µH 10µF Vendor The recommended PCB layout is shown in Figure 17. The inherently high peak currents and switching frequency of power supplies require careful PCB layout design. 10KΩ Figure 16. Setting the Output Voltage Inductor Selection The inductor parameters directly related to the device’s performances are saturation current and DC resistance. The FAN5308 operates with a typical inductor value of 3.3µH. The lower the DC resistance, the higher the efficiency. For saturation current, the inductor should be rated higher than the maximum load current plus half of the inductor ripple current. This is calculated as follows: 1 – ( V OUT ⁄ V IN ) ∆I L = V OUT × ----------------------------------------------L×f EQ. 4 Figure 17. Recommended PCB Layout Use wide traces for high-current paths and place the input capacitor, the inductor, and the output capacitor as close as possible to the integrated circuit terminals. To minimize voltage stress to the device resulting from everpresent switching spikes, use an input bypass capacitor with low ESR. Note that the peak amplitude of the switching spikes depends upon the load current; the higher the load current, the higher the switching spikes. The resistor divider that sets the output voltage should be routed away from the inductor to avoid RF coupling. The ground plane at the bottom side of the PCB acts as an electromagnetic shield to reduce EMI. where: ∆IL = Inductor Ripple Current f = Switching Frequency L = Inductor Value Inductor Value Vendor Part Number 3.3µH Panasonic ELL6PM3R3N 3.3µH Murata LQS66C3R3M04 Table 1: Recommended Inductors For more board layout recommendations, download the Fairchild application note PCB Grounding System and FAN2001/FAN2011 High-Performance DC-DC Converters (AN-42036). ©2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 9 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Applications Information FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter Mechanical Dimensions Dimensions are in millimeters unless otherwise noted. Figure 18. 3x3mm 6-Lead MLP © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 10 FAN5308 — 800mA High-Efficiency Step-Down DC-DC Converter © 2005 Fairchild Semiconductor Corporation FAN5308 Rev. 1.0.2 www.fairchildsemi.com 11