ISL8009A ® Data Sheet February 13, 2008 1.5A Low Quiescent Current 1.6MHz High Efficiency Synchronous Buck Regulator The ISL8009A is a high efficiency, monolithic, synchronous step-down DC/DC regulator that can deliver up to 1.5A continuous output current. It is optimized for generating low output voltages down to 0.8V. The supply voltage range of 2.7V to 5.5V, allows the use of single Li+cell, three NiMH cells or a regulated 5V input. The ISL8009A uses current mode control architecture to deliver very low duty cycle operation at high frequency with fast transient response and excellent loop stability. It has flexible operation mode selection of forced PWM mode and automatic PFM/PWM with as low as 17µA quiescent current, achieving high power conversion efficiency under light load condition, hence maximizing battery life. High 1.6MHz pulse-width modulation (PWM) switching frequency allows the use of small external components. FN6656.0 Features • High Efficiency Synchronous Buck Regulator with up to 95% Efficiency • 2ms Reset Timer • 2.7V to 5.5V Supply Voltage • 3% Output Accuracy Over-Temperature/Load/Line • 1.5A Guaranteed Output Current • 17µA Quiescent Supply Current in PFM Mode • Selectable Forced PWM Mode and PFM Mode • Less Than 1µA Logic Controlled Shutdown Current • 90% Maximum Duty Cycle for Lowest Dropout at 1.5A • Internal Current Mode Compensation • Internal Digital Soft-Start The ISL8009A integrates a pair of low ON-resistance P-Channel and N-Channel internal MOSFETs to maximize efficiency and minimize external component count. The 100% duty-cycle operation allows less than 400mV dropout voltage at 1.5A output current. • Peak Current Limiting, Short Circuit Protection The ISL8009A offers a 2ms Power-On-Reset (POR) timer at power-up. The timer output can be reset by RSI. When shutdown, ISL8009A discharges the output capacitor through a 100Ω resistor. Other features include internal digital soft-start, enable for power sequence, overcurrent protection, and thermal shutdown. • Small 8 Ld 2mmx3mm DFN The ISL8009A is offered in a 2mmx3mm 8 Ld DFN package with 1mm maximum height. The complete converter occupies less than 1cm2 area. • µC/µP, FPGA and DSP Power Ordering Information • Test and Measurement Systems PART NUMBER (Note) ISL8009AIRZ-T* TEMP. RANGE PART (°C) MARKING 09A PACKAGE (Pb-free) PKG. DWG. # • Over-Temperature Protection • Enable • Soft Discharge Disable • Pb-Free (RoHS Compliant) Applications • DC/DC POL Modules • Plug-in DC/DC Modules for Routers and Switchers • Portable Instruments Pinout ISL8009A (8 LD DFN) TOP VIEW -40 to +85 8 Ld 2x3 DFN L8.2x3 *Please refer to TB347 for details on reel specifications. NOTE: These Intersil Pb-free plastic packaged products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate PLUS ANNEAL - e3 termination finish, which is RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020. 1 VIN 1 8 LX EN 2 7 GND POR 3 6 VFB SKIP 4 5 RSI CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2008. All Rights Reserved All other trademarks mentioned are the property of their respective owners. ISL8009A Absolute Maximum Ratings (Reference to GND) Thermal Information Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.5V EN, RSI, SKIP, VFB, POR . . . . . . . . . . . . . . . . . -0.3V to VIN + 0.3V LX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -1.5V to 6.5V VFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.7V Thermal Resistance (Typical, Notes 1, 2) θJA (°C/W) θJC (°C/W) 8 Ld 2x3 DFN Package . . . . . . . . . . 65 6 Junction Temperature Range. . . . . . . . . . . . . . . . . .-55°C to +125°C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65°C to +150°C Pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/Pb-FreeReflow.asp Recommended Operating Conditions VIN Supply Voltage Range . . . . . . . . . . . . . . . . . . . . . . 2.7V to 5.5V Load Current Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0A to 1.5A Ambient Temperature Range . . . . . . . . . . . . . . . . . . .-40°C to +85°C CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact product reliability and result in failures not covered by warranty. NOTES: 1. θJA is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See Tech Brief TB379. 2. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside. 3. Limits established by characterization and are not production tested. Electrical Specifications Unless otherwise noted, all parameter limits are guaranteed over the recommended operating conditions and the typical specifications are measured at the following conditions: TA = +25°C, EN = VIN, RSI = SKIP = 0V, VIN = 5V, L = 2.2µH, C1 = C2 = 20µF, IOUT = 0A to 1.5A, unless otherwise noted. See “Typical Applications” on page 8. PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS Rising - 2.5 2.7 V Falling 2.2 2.4 - V SKIP = VIN, no load at the output - 17 30 µA SKIP = VIN, no load at the output and no switches switching, design info only - 15 - µA SKIP = GND, no load at the output - 3.7 6 mA VIN = 5.5V, EN = low - 0.1 2 µA 0.784 0.8 0.816 V INPUT SUPPLY VIN Undervoltage Lockout Threshold Quiescent Supply Current VUVLO IVIN Shutdown Supply Current ISD OUTPUT REGULATION VFB Regulation Voltage VVFB VFB Bias Current IVFB VFB = 0.75V - 0.1 - µA Output Voltage Accuracy VIN = VO + 0.5V to 5.5V, IO = 0A to 1A (Note 3) -3 - 3 % Line Regulation VIN = VO + 0.5V to 5.5V (minimal 2.7V) - 0.2 - %/V Adjustable version, design info only - 20 - µA/V VIN = 5.5V, IO = 200mA - 0.12 0.22 Ω VIN = 2.7V, IO = 200mA - 0.16 0.27 Ω VIN = 5.5V, IO = 200mA - 0.11 0.22 Ω VIN = 2.7V, IO = 200mA - 0.15 0.27 Ω 1.8 2.1 2.6 A 90 - - % 1.35 1.6 1.75 MHz - 70 100 ns - 1.1 - ms COMPENSATION Error Amplifier Trans-Conductance LX P-Channel MOSFET ON-Resistance N-Channel MOSFET ON-Resistance P-Channel MOSFET Peak Current Limit IPK IO = 1.5A LX Maximum Duty Cycle PWM Switching Frequency fS LX Minimum On-Time SKIP = low (forced PWM mode) Soft-Start-Up Time 2 FN6656.0 February 13, 2008 ISL8009A Electrical Specifications Unless otherwise noted, all parameter limits are guaranteed over the recommended operating conditions and the typical specifications are measured at the following conditions: TA = +25°C, EN = VIN, RSI = SKIP = 0V, VIN = 5V, L = 2.2µH, C1 = C2 = 20µF, IOUT = 0A to 1.5A, unless otherwise noted. See “Typical Applications” on page 8. (Continued) PARAMETER SYMBOL Soft-Discharge Resistor TEST CONDITIONS Enable = 0 MIN TYP MAX UNITS 80 100 120 Ω - - 0.3 V - 2 - ms - 0.01 0.1 µA POR Output Low Voltage Sinking 1mA, VFB = 0.7V Delay Time POR Pin Leakage Current POR = VIN = 3.6V Minimum Supply Voltage for Valid POR Signal 1.2 - - V Internal PGOOD Low Rising Threshold Percentage of nominal regulation voltage 89.5 92 94.5 % Internal PGOOD Low Falling Threshold Percentage of nominal regulation voltage 85 88 91 % Internal PGOOD High Rising Threshold Percentage of nominal regulation voltage 108 112 114 % Internal PGOOD High Falling Threshold Percentage of nominal regulation voltage 104 107 110 % - 50 - µs - - 0.4 V Internal PGOOD Delay Time EN, SKIP, RSI Logic Input Low Logic Input High 1.4 - - V - 0.1 1 µA Thermal Shutdown - 140 - °C Thermal Shutdown Hysteresis - 25 - °C Logic Input Leakage Current Pulled up to 5.5V Pin Descriptions VFB VIN Input supply voltage. Connect a 10µF ceramic capacitor to power ground. Buck regulator output feedback. Connect to the output through a resistor divider for adjustable output voltage (ISL8009A-ADJ). For preset output voltage, connect this pin to the output. RSI EN Regulator enable pin. Enable the output when driven to high. Shutdown the chip and discharge output capacitor when driven to low. Do not leave this pin floating. POR 2ms timer output. At power-up or EN HI, this output is a 2ms delayed Power-Good signal for the output voltage. This output can be reset by a low RSI signal. 2ms starts when RSI goes to high. SKIP Mode Selection pin. Connect to logic high or input voltage VIN for PFM mode; connect to logic low or ground for forced PWM mode. Do not leave this pin floating. This input resets the 2ms timer. When the output voltage is within the PGOOD window, an internal timer is started and generates a POR signal 2ms later when RSI is low. A high RSI resets POR and RSI high to low transition restarts the internal counter if the output voltage is within the window, otherwise the counter is reset by the output voltage condition. Exposed Pad The exposed pad must be connected to the GND pin for proper electrical performance. The exposed pad must also be connected to as much as possible for optimal thermal performance. LX Switching node connection. Connect to one terminal of inductor. GND System ground. 3 FN6656.0 February 13, 2008 ISL8009A Typical Operating Performance (Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V, EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) 100 100 90 90 70 2.5VOUT - PWM 1.5VOUT - PWM 60 EFFICIENCY (%) EFFICIENCY (%) 80 1.8VOUT - PWM 50 1.2VOUT - PWM 40 30 20 2.5VOUT - PFM 80 1.5VOUT - PFM 1.8VOUT - PFM 70 1.2VOUT - PFM 60 50 10 0 0.00 0.25 0.50 0.75 1.00 1.25 40 0.05 1.50 0.10 0.15 0.20 OUTPUT LOAD (A) 0.25 0.30 0.35 0.40 0.45 0.50 OUTPUT LOAD (A) FIGURE 1. EFFICIENCY vs LOAD, VIN = 3.3V PWM FIGURE 2. EFFICIENCY vs LOAD, VIN = 3.3V PFM 100 100 90 90 70 2.5VOUT - PWM 1.5VOUT - PWM 60 1.8VOUT - PWM 50 EFFICIENCY (%) EFFICIENCY (%) 80 3.3VOUT - PWM 40 30 1.2VOUT - PWM 20 2.5VOUT - PFM 80 3.3VOUT - PFM 1.5VOUT - PFM 70 1.8VOUT - PFM 60 1.2VOUT - PFM 50 10 0 0.00 0.25 0.50 0.75 1.00 1.25 40 0.05 1.50 0.15 0.25 FIGURE 3. EFFICIENCY vs LOAD, VIN = 5V PWM 0.45 0.55 0.65 0.75 FIGURE 4. EFFICIENCY vs LOAD, VIN = 5V PFM 1.54 1.24 2.8VIN - PWM 5VIN - PWM 1.53 5VIN - PFM 1.22 1.21 3.3VIN-PFM 1.20 1.19 1.18 3.3VIN - PWM 2.8VIN - PFM 1.52 2.8VIN - PWM 5VIN - PWM 5VIN - PFM 1.51 1.50 3.3VIN-PFM 1.49 1.48 3.3VIN - PWM 2.8VIN - PFM 1.47 1.17 1.16 0.00 OUTPUT VOLTAGE (V) 1.23 OUTPUT VOLTAGE (V) 0.35 OUTPUT LOAD (A) OUTPUT LOAD (A) 0.25 0.50 0.75 1.00 OUTPUT LOAD (A) 1.25 FIGURE 5. VOUT REGULATION vs LOAD, VOUT = 1.2V 4 1.50 1.46 0.00 0.25 0.50 0.75 1.00 1.25 1.50 OUTPUT LOAD (A) FIGURE 6. VOUT REGULATION vs LOAD, VOUT = 1.5V FN6656.0 February 13, 2008 ISL8009A Typical Operating Performance (Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V, EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued) 1.84 2.54 2.53 5.5VIN - PFM 5.5VIN - PWM 1.82 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 1.83 1.81 2.7VIN - PWM 1.80 4VIN-PFM 1.79 1.78 4VIN - PWM 1.77 1.76 0.00 0.25 2.7VIN - PFM 2.51 2.50 2.49 0.50 0.75 1.00 OUTPUT LOAD (A) 1.25 2.46 0.00 1.50 0.25 0.50 0.75 1.00 OUTPUT LOAD (A) 1.25 1.50 FIGURE 8. VOUT REGULATION vs LOAD, VOUT = 2.5V 0.7 2.8VIN - PWM 4VIN - PWM 3.38 5.5VIN - PFM POWER DISSIPATION (W) OUTPUT VOLTAGE (V) 3.3VIN - PWM 2.47 3.42 5.5VIN - PWM 3.36 3.34 3.32 4VIN - PFM 3.3VIN - PWM 5VIN-PFM 3.30 0.6 0.5 0.4 0.3 2.8VIN - PFM 0.2 3.3VIN - PWM 3.3VIN-PFM 5VIN - PWM 3.28 0.1 3.26 0.00 0.0 0.00 5VIN - PFM 0.25 0.50 0.75 1.00 OUTPUT LOAD (A) 1.25 1.50 FIGURE 9. VOUT REGULATION VS LOAD, VOUT = 3.3V 0.25 0.50 0.75 1.00 OUTPUT LOAD (A) 1.25 1.50 FIGURE 10. POWER DISSIPATION vs LOAD, 1.6 MHz, VOUT = 1.8V 45 2.5 0.75A LOAD 40 NO LOAD- PWM 35 OUTPUT VOLTAGE (V) POWER DISSIPATION (mW) 3.3VIN - PFM 2.48 FIGURE 7. VOUT REGULATION vs LOAD, VOUT = 1.8V 3.40 5VIN - PFM 5VIN - PWM 2.52 30 25 20 15 NO LOAD - PFM 10 2.0 1.5 1.5A LOAD 1.0 NO LOAD 0.5 5 0 2.75 3.25 3.75 4.25 4.75 5.25 VIN (V) FIGURE 11. POWER DISSIPATION vs VIN AT NO LOAD, VOUT = 1.8V 5 0.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) FIGURE 12. OUTPUT VOLTAGE REGULATION vs VIN PWM MODE FN6656.0 February 13, 2008 ISL8009A Typical Operating Performance (Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V, EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued) OUTPUT VOLTAGE (V) 2.0 NO LOAD 1.5 0.75A LOAD 1.0 LX 2V/DIV 1.5A LOAD 0.5 VOUT RIPPLE 20mV/DIV 0.0 -0.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 IL 0.2A/DIV INPUT VOLTAGE (V) FIGURE 13. OUTPUT VOLTAGE REGULATION vs VIN SKIP MODE FIGURE 14. STEADY STATE OPERATION AT NO LOAD (PWM), 1µs/DIV LX 2V/DIV VOUT RIPPLE 20mV/DIV LX 2V/DIV IL 0.5A/DIV VOUT RIPPLE 20mV/DIV IL 0.2A/DIV FIGURE 15. STEADY STATE OPERATION AT NO LOAD (PFM), 1µs/DIV FIGURE 16. STEADY STATE OPERATION WITH FULL LOAD, 1µs/DIV LX 2V/DIV LX 2V/DIV VOUT RIPPLE 50mV/DIV IL 1A/DIV VOUT RIPPLE 50mV/DIV IL 1A/DIV FIGURE 17. LOAD TRANSIENT (PWM), 200µs/DIV 6 FIGURE 18. LOAD TRANSIENT (PFM), 200µs/DIV FN6656.0 February 13, 2008 ISL8009A Typical Operating Performance (Unless otherwise noted, operating conditions are: TA = +25°C, VVIN = 5V, EN = VIN, RSI = SKIP = 0V, L = 2.2µH, C1 = 20µF, C2 = 20µF, IOUT = 0A) (Continued) EN 2V/DIV EN 2V/DIV VOUT 1V/DIV VOUT 0.5V/DIV IL 1A/DIV IL 1A/DIV POR 1V/DIV POR 2V/DIV FIGURE 19. SOFT-START AT NO LOAD, 500µs/DIV FIGURE 20. SOFT-START WITH PRE-BIASED 1V, 500µs/DIV LX 2V/DIV EN 2V/DIV VOUT 0.5V/DIV IL 0.5A/DIV IL 1A/DIV VOUT 1V/DIV POR 5V/DIV POR 2V/DIV FIGURE 21. SOFT-START AT FULL LOAD, 500µs/DIV FIGURE 22. OUTPUT SHORT CIRCUIT, 10.0µs/DIV VOUT 1V/DIV IL 1A/DIV POR 5V/DIV FIGURE 23. OUTPUT SHORT CIRCUIT RECOVERY, 500µs/DIV 7 FN6656.0 February 13, 2008 ISL8009A Typical Applications L 2.2µH INPUT 2.7V TO 5.5V VIN OUTPUT 1.8V TO 1.5A LX C2 20µF C1 20µF R2 124k GND ISL8009A EN R3 100k R1 100k POR VFB SKIP RSI FIGURE 24. TYPICAL APPLICATION DIAGRAM Block Diagram SKIP BANDGAP 390k 0.8V VIN OSCILLATOR EAMP + EN SHUTDOWN 27pF SOFT- START SHUTDOWN + COMP PWM/PFM LOGIC CONTROLLER PROTECTION DRIVER + LX GND VFB SLOP SLOPE E COMP COMP 0.864V + + CSA1 + OCP 0.85V + 0.736V + SKIP POR 2ms DELAY 0.17V ZERO - CROSS SENSING RSI 0.2V SCP + FIGURE 25. FUNCTIONAL BLOCK DIAGRAM 8 FN6656.0 February 13, 2008 ISL8009A Theory of Operation The ISL8009A is a step-down switching regulator optimized for battery-powered handheld applications. The regulator operates at 1.6MHz fixed switching frequency under heavy load condition to allow small external inductor and capacitors to be used for minimal printed-circuit board (PCB) area. At light load, the regulator reduces the switching frequency, unless forced to the fixed frequency to minimize the switching loss and to maximize the battery life. The quiescent current when the output is not loaded is typically only 17µA. The supply current is typically only 0.1µA when the regulator is shutdown. The output voltage is regulated by controlling the reference voltage to the current loop. The bandgap circuit outputs a 0.8V reference voltage to the voltage control loop. The feedback signal comes from the VFB pin. The soft-start block only affects the operation during the start-up and will be discussed separately. The error amplifier is a transconductance amplifier that converts the voltage error signal to a current output. The voltage loop is internally compensated with the 30pF and 300kΩ RC network. The maximum EAMP voltage output is precisely clamped to the bandgap voltage (1.172V). VEAMP PWM Control Scheme The ISL8009A employes the current-mode pulse-width modulation (PWM) control scheme for fast transient response and pulse-by-pulse current limiting. Figure 25 shows the block diagram. The current loop consists of the oscillator, the PWM comparator COMP, the current sensing circuit, and the slope compensation for the current loop stability. The current sensing circuit consists of the resistance of the P-Channel MOSFET when it is turned on and the current sense amplifier CSA. The gain for the current sensing circuit is typically 0.4V/A. The control reference for the current loops comes from the error amplifier EAMP of the voltage loop. The PWM operation is initialized by the clock from the oscillator. The P-Channel MOSFET is turned on at the beginning of a PWM cycle and the current in the MOSFET starts to ramp up. When the sum of the current amplifier CSA and the compensation slope (0.675V/µs) reach the control reference of the current loop, the PWM comparator COMP sends a signal to the PWM logic to turn off the P-MOSFET and to turn on the N-Channel MOSFET. The N-MOSFET stays on until the end of the PWM cycle. Figure 26 shows the typical operating waveforms during the PWM operation. The dotted lines illustrate the sum of the compensation ramp and the current-sense amplifier CSA output. VCSA1 Duty DUTY Cycle CYCLE IL VOUT FIGURE 26. PWM OPERATION WAVEFORMS SKIP Mode The ISL8009A enters a pulse-skipping mode at light load to minimize the switching loss by reducing the switching frequency. Figure 27 illustrates the skip-mode operation. A zero-cross sensing circuit shown in Figure 25 monitors the N-MOSFET current for zero crossing. When 8 consecutive cycles of the N-MOSFET crossing zero are detected, the regulator enters the skip mode. During the 8 detecting cycles, the current in the inductor is allowed to become negative. The counter is reset to zero when the current in any cycle does not cross zero. CLOCK Clock 88CYCLES Cycles CURRENT LIMIT Current Limit IL LOAD LoadCURRENT Current 0 NOMINAL++1.5% Nominal 1.5% VOUT NOMINAL Nominal FIGURE 27. SKIP MODE OPERATION WAVEFORMS 9 FN6656.0 February 13, 2008 ISL8009A Once the skip mode is entered, the pulse modulation starts being controlled by the SKIP comparator shown in Figure 25. Each pulse cycle is still synchronized by the PWM clock. The P-MOSFET is turned on at the clock and turned off when its current reaches 20% of the current limit value (0.2V at the CSA output). As the average inductor current in each cycle is higher than the average current of the load, the output voltage rises cycle over cycle. When the output voltage reaches 1.5% above the nominal voltage, the P-MOSFET is turned off immediately and the inductor current is fully discharged to zero and stays at zero. The output voltage reduces gradually due to the load current discharging the output capacitor. When the output voltage drops to the nominal voltage, the P-MOSFET will be turned on again at the clock, repeating the previous operations. The regulator resumes normal PWM mode operation when the output voltage drops 1.5% below the nominal voltage. . VO MIN 25ns RSI 2ms 2ms POR FIGURE 28. RSI AND POR TIMING DIAGRAM UVLO When the input voltage is below the undervoltage lock out (UVLO) threshold, the regulator is disabled. Soft-Start-Up The ISL8009A has a SKIP pin that controls the operation mode. When the SKIP pin is driven to low or shorted to ground, the regulator operates in a forced PWM mode. The forced PWM mode remains the fixed PWM frequency at light load instead of entering the skip mode. The soft start-up eliminates the in-rush current during the start-up. The soft-start block outputs a ramp reference to both the voltage loop and the current loop. The two ramps limit the inductor current rising speed as well as the output voltage speed so that the output voltage rises in a controlled fashion. At the very beginning of the start-up, the output voltage is less than 0.2V; hence the PWM operating frequency is 1/3 of the normal frequency. Overcurrent Protection Power MOSFETs The overcurrent protection is realized by monitoring the CSA output with the OCP comparator, as shown in Figure 25. The current sensing circuit has a gain of 0.4V/A, from the N-MOSFET current to the CSA output. When the CSA output reaches 0.8V, (which is equivalent to 2A for the switch current) the OCP comparator is tripped to turn off the P-MOSFET immediately. The power MOSFETs are optimized for best efficiency. The ON-resistance for the P-MOSFET is typically 120mΩ and the ON-resistance for the N-MOSFET is typically 110mΩ. Mode Control Short-Circuit Protection A short-circuit protection SCP comparator monitors the VFB pin voltage for output short-circuit protection. When the VFB is lower than 0.2V, the SCP comparator forces the PWM oscillator frequency to drop to 1/3 of the normal operation value. This comparator is effective during start-up or an output short-circuit event. RSI/POR Function When powering up, the open-collector Power-On-Reset output holds low for about 1ms after VO reaches the preset voltage. When the active-HI reset signal RSI is issued, POR goes to low immediately and holds for the same period of time after RSI comes back to LOW. The output voltage is unaffected (refer to Figure 28). When the function is not used, connect RSI to ground and leave the pull-up resistor, R4, open at the POR pin. The POR output also serves as a 1ms delayed Power-Good signal when the pull-up resistor, R4, is installed. The RSI pin needs to be directly (or indirectly through resistor, R5) connected to ground for this to function properly. 10 Duty Cycle The ISL8009A features duty cycle operation to maximize the battery life. When the battery voltage drops to a level that the ISL8009A can no longer maintain the regulation at the output, the regulator completely turns on the P-MOSFET. The maximum drop out voltage under the duty-cycle operation is the product of the load current and the ON-resistance of the P-MOSFET. Enable The Enable (EN) input allows the user to control the turning on or off of the regulator for purposes such as power-up sequencing. When the regulator is enabled, there is typically a 600µs delay for waking up the bandgap reference, then the soft-start-up begins. When the regulator is disabled, the P-MOSFET and the N-MOSFET are turned off immediately. The 100Ω soft discharge resistor from LX to GDN is activated and pulls the output to 0V. Thermal Shutdown The ISL8009A has built-in thermal protection. When the internal temperature reaches +140°C, the regulator is completely shutdown. As the temperature drops to +120°C, the ISL8009A resumes operation by stepping through a soft-start-up. FN6656.0 February 13, 2008 ISL8009A Applications Information Output Voltage Setting Resistor Selection Output Inductor and Capacitor Selection To consider steady state and transient operation, ISL8009A typically uses a 3.3µH output inductor. Higher or lower inductor values can be used to optimize the total converter system performance. For example, for higher output voltage 3.3V application, in order to decrease the inductor current ripple and output voltage ripple, the output inductor value can be increased. The inductor ripple current can be expressed in Equation 1: VO ⎞ ⎛ V O • ⎜ 1 – ---------⎟ V IN⎠ ⎝ ΔI = --------------------------------------L • fS (EQ. 1) The inductor’s saturation current rating needs be at least larger than the peak current. The ISL8009A protects the typical peak current 2.1A. The saturation current needs to be over 2.4A for maximum output current application. ISL8009A uses internal compensation network and the output capacitor value is dependant on the output voltage. The ceramic capacitor is recommended to be X5R or X7R. The recommended minimum output capacitor values are shown in Table 1. TABLE 1. OUTPUT CAPACITOR VALUE vs VOUT VOUT (V) COUT (µF) L (µH) 0.8 10 1.0~2.2 1.2 10 1.2~2.2 1.6 10 1.8~2.2 1.8 10 1.8~3.3 2.5 10 1.8~3.3 3.3 10 1.8~4.7 3.6 10 1.8~4.7 The resistors R2 and R3 shown in Figure 24 set the output voltage for the adjustable version. The output voltage can be calculated by Equation 2: R 2⎞ ⎛ V O = 0.8 • ⎜ 1 + -------⎟ R 3⎠ ⎝ (EQ. 2) where the 0.8V is the reference voltage. The voltage divider consists of R2 and R3 and increases the quiescent current by VO/(R2 + R3), so larger resistance is desirable. On the other hand, the VFB pin has leakage current that will cause error in the output voltage setting. The leakage current has a typical value of 0.1µA. To minimize the accuracy impact on the output voltage, select the R3 no larger than 200kΩ. For VO = 0.8V, it is recommended to short R2 and open R3. Layout Recommendation The layout is a very important converter design step to make sure the designed converter works well. For the ISL8009A buck converter, the power loop is composed of the output inductor L, the output capacitor COUT, the LX pin and the GND pin. It is necessary to make the power loop as small as possible. The heat of the IC is mainly dissipated through the thermal pad. Maximizing the copper area connected to the thermal pad is preferable. In addition, a solid ground plane is helpful for EMI performance. It is recommended to add 5 vias under the thermal pad connection to the solid ground plane. In Table 1, the minimum output capacitor value is given for different output voltages to make sure the whole converter system is stable. Input Capacitor Selection The main functions for the input capacitor are to provide decoupling of the parasitic inductance and to provide filtering function to prevent the switching current from flowing back to the battery rail. A 10µF, X5R or X7R ceramic capacitor is a good starting point for the input capacitor selection. 11 FN6656.0 February 13, 2008 ISL8009A Dual Flat No-Lead Plastic Package (DFN) L8.2x3 8 LEAD DUAL FLAT NO-LEAD PLASTIC PACKAGE MILLIMETERS 2X SYMBOL 0.15 C A A D 2X 0.15 C B MIN 0.80 0.90 1.00 - - - 0.05 - 0.32 5,8 1.75 7,8 1.90 7,8 0.20 REF 0.20 D D2 INDEX AREA B 0.10 A SIDE VIEW C SEATING PLANE - 1.65 - 3.00 BSC 1.65 e // 0.25 2.00 BSC 1.50 E E2 TOP VIEW NOTES A b E MAX A1 A3 6 NOMINAL 1.80 - 0.50 BSC - k 0.20 - - - L 0.30 0.40 0.50 8 C 0.08 C N 8 Nd 4 A3 2 3 Rev. 0 6/04 NOTES: 1. Dimensioning and tolerancing conform to ASME Y14.5-1994. D2 (DATUM B) 7 8 2. N is the number of terminals. 3. Nd refers to the number of terminals on D. D2/2 1 6 INDEX AREA 4. All dimensions are in millimeters. Angles are in degrees. 2 NX k (DATUM A) 6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature. E2 E2/2 7. Dimensions D2 and E2 are for the exposed pads which provide improved electrical and thermal performance. NX L 8. Nominal dimensions are provided to assist with PCB Land Pattern Design efforts, see Intersil Technical Brief TB389. N N-1 NX b e 8 5. Dimension b applies to the metallized terminal and is measured between 0.25mm and 0.30mm from the terminal tip. 5 0.10 (Nd-1)Xe REF. M C A B BOTTOM VIEW CL (A1) NX (b) L 5 SECTION "C-C" C C TERMINAL TIP e FOR EVEN TERMINAL/SIDE All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries. For information regarding Intersil Corporation and its products, see www.intersil.com 12 FN6656.0 February 13, 2008