FAN5332ASX

FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch August 2005 FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch Features ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 1.5MHz Switching Frequency Low Noise Adjustable Output Voltage Up to 1.5A Peak Switch Current 1.5W Output Power Capability Low Shutdown Current: 18.5V, VIN ≥ 2.7V VOUT > 19.7V, VIN ≥ 3.2V, TON < 0.4Sec. VIN = 5V VIN = 3.6V VSHDN = 3.6V, No Switching VSHDN = 3.6V, Switching, VOUT = 20.7V VSHDN = 0V Device ON Device OFF VSHDN = 0V or VSHDN = 5.5V TA= 25°C 1.205 1 1.230 1 0.5 0.8 1.5 93 1.5 1.5 5 5 1 1.8 1.5 0.5 100 1.255 100 1.5 Conditions Min. -3 1.1 50 75 Typ. 1.5 Max. +3 Units % A mA mA 0.6 0.7 0.7 4.5 0.1 3 Ω Ω mA mA µA V V nA V nA % % MHz % mS mS µA Test Circuit VIN CIN 10µF 5 V 1 R1 160KΩ CF 82pF 2.7V to 5.5V L 6.8µH BAT54 COUT 2.2µF VOUT SW FAN5332A IN FB 3 R2 ON OFF 4 SHDN GND 2 10KΩ Figure 3. Test Circuit 4 FAN5332A Rev. 1.0.1 www.fairchildsemi.com FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch Typical Performance Characteristics TA = 25°C, CIN = 10µF, COUT = 2.2µF, L = 6.8µH, unless otherwise noted. Line Regulation 22 R OUT = 275Ω Full Load Efficiency 90 R OUT = 275Ω Output Voltage (V) 21 80 20 TA = 25°C TA = 85°C Efficiency (%) 70 TA = 25°C T A = 85°C 19 TA = -40°C 60 TA = -40°C 18 2.5 3.0 3.5 4.0 4.5 5.0 5.5 50 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Battery Voltage (V) Battery Voltage (V) No Load Battery Current vs. Battery Voltage 6 TA = 25°C Light Load Efficiency 85 I Load = 20mA 5 Battery Current (mA) 80 TA = 85°C 4 3 2 1 0 2.5 Efficiency (%) 75 I Load = 10mA TA = -40°C 70 65 3.0 3.5 4.0 4.5 5.0 5.5 60 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Battery Voltage (V) Battery Voltage (V) Load Transient Response V IN = 3.6V VOUT = 20.7V ROUT = 275Ω Start-Up Response Output Voltage (5V/ div ) ENABLE Inductor Voltage Current (5V/d iv) (50 0mA/di v) VIN = 3.6V Output Voltage (500m V/d iv) Load Regulation Load Current Step 75 mA 0mA Time (100 µs/div ) Tim e (500 µs/div) 5 FAN5332A Rev. 1.0.1 www.fairchildsemi.com FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch Block Diagram SHDN 4 Shutdown Circuitry VIN 5 SW 1 FB + Over Voltage - Comp 1.15 x VREF Thermal Shutdown R FB 3 + Error Amp Σ + Comp - R R S Q Driver n Ramp Generator Oscillator Current Limit Comparator - + + Amp Reference Soft-Start 0.03W 2 GND Figure 4. Block Diagram Circuit Description The FAN5332A is a pulse-width modulated (PWM) current-mode boost converter. The FAN5332A improves the performance of battery-powered equipment by significantly minimizing the spectral distribution of noise at the input caused by the switching action of the regulator. To facilitate effective noise filtering, the switching frequency was chosen to be high, 1.6MHz. An internal soft start circuitry minimizes in-rush currents. The timing of the soft start circuit was chosen to reach 95% of the nominal output voltage within maximum 5mS following an enable command when VIN = 2.7V, VOUT = 20.7V, ILOAD = 35mA and COUT (EFFECTIVE) =2.2µF. The device architecture is that of a current mode controller with an internal sense resistor connected in series with the N-channel switch. The voltage at the feedback pin tracks the output voltage at the cathode of the external Schottky diode (shown in the test circuit). The error amplifier amplifies the difference between the feedback voltage and the internal bandgap reference. The amplified error voltage serves as a reference voltage to the PWM comparator. The inverting input of the PWM comparator consists of the sum of two components: the amplified control signal received from the 30mΩ current sense resistor and the ramp generator voltage derived from the oscillator. The oscillator sets the latch, and the latch turns on the FET switch. Under normal operating conditions, the PWM comparator resets the latch and turns off the FET, thus terminating the pulse. Since the comparator input contains information about the output voltage and the control loop is arranged to form a negative feedback loop, the value of the peak inductor current will be adjusted to maintain regulation. Every time the latch is reset, the FET is turned off and the current flow through the switch is terminated. The latch can be reset by other events as well. Over-current condition is monitored by the current limit comparator which resets the latch and turns off the switch instantaneously within each clock cycle. Over-voltage condition is detected by a fast comparator limiting the duty cycle in a similar manner to over-current monitoring described above. Dimming may be accomplished by PWM modulating the SHDN input at a frequency around 100Hz. Over-Voltage Protection The voltage on the feedback pin is sensed by an OVP Comparator. When the feedback voltage is 15% higher than the nominal voltage, the OVP Comparator stops switching of the power transistor, thus preventing the output voltage from going higher. Applications Information Setting the Output Voltage The internal reference (VREF) is 1.23V (Typical). The output voltage is divided by a resistor divider, R1 and R2 to the FB pin. The output voltage is given by R1 V OUT = V REF  1 + ------  R 2 According to this equation, and assuming desired output voltage of 20.7V, good choices for the feedback resistors are, R1=160kΩ and R2=10kΩ. Inductor Selection The inductor parameters directly related to device performances are saturation current and dc resistance. The FAN5332A operates with a typical inductor value of 6.8µH. The lower the dc resistance, the higher the efficiency. Usually a trade-off between 6 FAN5332A Rev. 1.0.1 www.fairchildsemi.com FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch inductor size, cost and overall efficiency is needed to make the optimum choice. The inductor saturation current should be rated around 1.5A, which is the threshold of the internal current limit circuit. This limit is reached only during the start-up and with heavy load condition; when this event occurs the converter can shift over in discontinuous conduction mode due to the automatic turn-off of the switching transistor, resulting in higher ripple and reduced efficiency. Some recommended inductors are suggested in the table below: ered in applications such as a flash LED driver. An operation time of 0.4Sec. at maximum load, followed by a 3.6Sec. OFF time ensures stable operation even in the worst case, provided that the IC heat dissipation is optimized to lower the junction to ambient thermal resistance. The external passive components and the layout of the PCB play an important role in reaching the highest efficiency of the boost converter. For best results, the data sheet recommendations regarding external components and PCB layout should be followed closely. PCB Layout Recommendations The inherently high peak currents and switching frequency of power supplies require careful PCB layout design. Therefore, 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. The resistor divider that sets the output voltage should be routed away from the inductor to avoid RF coupling. A two layer PCB with the bottom layer as ground plane connected to the pin 2 of the IC is recommended. This ground plane acts as an electromagnetic shield to reduce EMI and parasitic coupling between components. Inductor Value Vendor 6.8µH 6.8µH 6.8µH TDK MURATA COOPER Part Number SLF7028T6R8M1R3 LQ566C6R8M04 SD414-6R8 Comment Low Profile High Efficiency Small Size Table 1: Recommended Inductors Capacitors Selection For best performance, low ESR input and output capacitors are required. Ceramic capacitors of CIN = 10µF and COUT = 2.2µF placed as close to the IC pins, are recommended for the lower input and output ripple. The output capacitor voltage rating should be according to the VOUT setting. Some capacitors are suggested in the table below. Capacitor Value 10µF 2.2µF Vendor Murata Murata Part Number GRM31CR70J106KA01B GRM32RR71E225KC01B Table 2: Recommended Capacitors A feed forward capacitor CF, is required for stability. The recommended value (R1 x CF) is around 13µS. Figure 5. Recommended PCB Layout Diode Selection The external diode used for rectification is usually a Schottky diode. Its average forward current and reverse voltage maximum ratings should exceed the load current and the voltage at the output of the converter respectively. A barrier Schottky diode such as BAT54 is preferred, due to its lower reverse current over the temperature range. Care should be taken to avoid any short circuit of VOUT to GND, even with the IC disabled, since the diode can be instantly damaged by the excessive current. Thermal Shutdown When the die temperature exceeds 150°C, a reset occurs and will remain in effect until the die cools to 130°C, at that time the circuit will be allowed to restart. Heavy Load Limitations In heavy load applications (POUT >1.5W) the power dissipated in steady state at high ambient temperature can increase the die temperature to the point where the thermal shutdown kicks in. To prevent this, a limited time operation should be consid- 7 FAN5332A Rev. 1.0.1 www.fairchildsemi.com FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch Mechanical Dimensions 5-Lead SOT-23Package B e c E H e1 D A A1 L Symbol Min A A1 B c D E e e1 H L α .087 .004 0º .035 .000 .008 .003 .106 .059 Inches Max .057 .006 .020 .010 .122 .071 .037 BSC .075 BSC .126 .024 10º Millimeters Min .90 .00 .20 .08 2.70 1.50 .95 BSC 1.90 BSC 2.20 .10 0º 3.20 .60 10º Notes Max 1.45 .15 .50 .25 3.10 1.80 Ordering Information Product Number FAN5332A Package Type 5-Lead SOT23 Order Code FAN5332ASX 8 FAN5332A Rev. 1.0.1 www.fairchildsemi.com FAN5332A High Efficiency, High Current Serial LED Driver and OLED Supply with 30V Integrated Switch TRADEMARKS The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and is not intended to be an exhaustive list of all such trademarks. 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PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Advance Information Product Status Formative or In Design Definition This datasheet contains the design specifications for product development. Specifications may change in any manner without notice. This datasheet contains preliminary data, and supplementary data will be published at a later date. Fairchild Semiconductor reserves the right to make changes at any time without notice in order to improve design. This datasheet contains final specifications. Fairchild Semiconductor reserves the right to make changes at any time without notice in order to improve design. Preliminary First Production No Identification Needed Full Production Obsolete Not In Production This datasheet contains specifications on a product that has been discontinued by Fairchild semiconductor. The datasheet is printed for reference information only. Rev. I16 9 FAN5332A Rev. 1.0.1 www.fairchildsemi.com