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| A8483 Package EK: MLP/TDFN, 3 x 3 mm 0.75 mm Nominal Height 1.2 MHz Step-up Converter for Display Bias Supply The A8483 is a current mode step-up dc-to-dc converter, available in a 5-pin 3 mm x 3 mm thermally enhanced MLP/TDFN lead (Pb) free package. Smaller external components and integrated 36 V switch reduce component count and footprint for a variety of applications. APPLICATIONS OLED bias supply / WLED backlight Portable battery-powered equipment Cellular phones PDAs (Personal Digital Assistant) Camcorders, personal stereos, MP3 players, cameras Mobile GPS systems Approximate Scale 1:1 FEATURES Output voltage up to 35 V 2.5 to 10 V input 0.9 to 18 V input with separate bias supply Delivers 15 V at 15 mA with 2.7 V input Constant 1.2 MHz switching frequency provides low noise 350 mA switch current limit 1 A shutdown current Low-noise PWM/analog dimming VOUT 5 VIN VSUPPLY C1 1 F EN 4 Enable R2 39 k L1 10 H 1 SW D1 IOUT1 + IOUT2 = 15 mA 5 VIN L1 10 H 1 SW D1 R1 732 k FB 3 VOUT2 R2 39 k D2 -12 V VOUT1 +12 V OLED A8483 GND 2 FB 3 R1 820 k C2 1 F VSUPPLY C1 1 F EN 4 Enable A8483 GND 2 C2 0.47 F C3 0.47 F Li-ion 2.5 V to 5.5 V Li-ion 2.5 V to 5.5 V C4 0.47 F Figure 1. OLED Bias Supply. Use for cell phones, MP3 players, DSCs, and PDAs. 32 V, 18 mA VOUT 5 VIN VSUPPLY C1 1 F 5V EN 4 Enable R2 15 k L1 10 H 1 SW D1 R1 768 k for VOUT = 32 V 604 k for VOUT = 25 V 25 V, 25 mA Figure 2. Small LCD Bias Supply. Li+ battery to 12 V. Connect either VZ or VBIAS VZ 7.5 V L1 22 H 1 SW D1 R1 768 k for VOUT = 32 V 604 k for VOUT = 25 V R2 15 k VOUT 32 V, 40 mA 25 V, 80 mA A8483 GND 2 FB 3 C2 1 / 50 V F VSUPPLY 12 V C1 1 F VBIAS 5V 5 VIN EN 4 Enable A8483 GND 2 FB 3 C2 1 / 50 V F C3 0.1 F Figure 3. LCD TV, Plasma TV Bias, FED Display, Varactor Diode Bias. Using 5 V input. VOUT 5 VIN VSUPPLY C1 1 F EN 4 Enable Cf 0.01 F L1 10 H 1 SW D1 C2 0.22 F VC Analog Voltage or PWM R1 47 Figure 4. LCD TV, Plasma TV Bias, FED Display, Varactor Diode Bias. Using 12 V input. VOUT 5 VIN L1 10 H 1 SW D1 R1 560 k FB 3 R3 160 k R2 47 k Cf 1 nF C2 1 F OLED Cf for PWM dimming only VC A8483 GND 2 FB 3 R2 5 k R3 24 k VSUPPLY Li-ion 2.5 V to 5.5 V C1 1 F EN 4 Enable A8483 GND 2 Li-ion 2.5 V to 5.5 V Figure 5. WLED Backlighting. A8483-DS, Rev. 1 Analog Voltage or PWM 10 kHz Figure 6. OLED Bias Supply. Use for low-noise PWM dimming, or with analog voltage through the FB pin. A8483 1.2 MHz Step-up Converter for Display Bias Supply Functional Block Diagram FB SW A1 VIN VREF 1.25 V 615 mV RC CC A2 R S Q Driver Ramp Generator EN Enable 1.2 MHz Oscillator GND Terminal List Table Pin 1 2 3 4 5 Name SW GND FB EN VIN Function Internal power FET Ground Feedback input Enable input Input supply Device Pin-out Diagram SW 1 GND 2 FB 3 5 VIN 4 EN Absolute Maximum Ratings SW Pin ..................................................................................-0.3 to 36 V Remaining Pins .................................................................... -0.3 to 10 V Operating Ambient Temperature , TA .................................... -40C to 85C Junction Temperature, TJ(max)............................................................. 150C Storage Temperature, TS .................................................. -55C to 150C Package Thermal Characteristics RJA = 50 C/W, on a 4-layer board. Additional information is available on the Allegro Web site. A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 2 A8483 Characteristics Input Voltage Range Supply Current Feedback Reference Voltage Feedback Input Current Switch Current Limit Switch Frequency Switch Maximum Duty Cycle Switch Saturation voltage Switch Leakage Current Enable Input Input Threshold Low Input Threshold High Input Leakage 1.2 MHz Step-up Converter for Display Bias Supply Symbol VIN ISUP VFB IFB ISWLIM FSW D VCE(SAT) ISL VIL VIH Leakage - Active: IOUT = 15 mA, VOUT = 12 V Shutdown (EN = 0 V) - VFB = 0.615 V - - - ISW = 0.2 A VSW = 36 V - - IIL Test Conditions Min. 2.5 - - 590 - - 0.8 85 - - - 1.5 - Typ. - 2.5 0.1 615 50 350 1.2 90 350 - - - - Max. 10 3.5 1 640 100 - 1.6 - - 5 0.4 - 1 Units V mA A mV nA mA MHz % mV A V V A ELECTRICAL CHARACTERISTICS at TA = 25C, VIN = 3 V (unless otherwise noted) Operating Characteristics (VIN = 3 V) Efficiency versus Input Voltage VOUT = 15 V; Toko 1098AS-100M Inductor Feedback Bias Current versus Temperature VFB = 0.615 V 90 85 80 Efficiency (%) IFB (nA) 10 65 62 59 56 53 50 2 3 4 5 6 VIN (V) 7 8 9 -50 0 50 Temperature (C) 100 150 75 70 65 60 55 50 IOUT (mA) 25 15 2 Switching Frequency versus Temperature 1.25 1.20 FSW (MHz) Quiescent Supply Current versus Temperature 2.6 2.5 ISUPQ (mA) 1.15 1.10 1.05 1.00 -50 0 50 Temperature (C) 100 150 2.4 2.3 2.2 2.1 -50 0 50 Temperature (C) Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 100 150 3 A8483-DS, Rev. 1 A8483 1.2 MHz Step-up Converter for Display Bias Supply Functional Description Pin Functions VIN. Supply to the control circuit. A bypass capacitor, C1, must be connected from close to this pin to GND. GND. Ground reference connected directly to the ground plane. The feedback resistor should have a separate connection directly to this point. EN. Voltage lower than 0.4 V disables the A8483 and puts the control circuit into the low-power sleep mode. Voltage greater than 1.5 V fully enables the A8483. SW. Low-side switch connection between the inductor, L1, and ground. Because rapid changes of current occur at this pin, the traces on the PCB that are connected to this pin should be minimized. In addition, L1 and the diode, D1, should be connected as close to this pin as possible. FB. Feedback pin for OLED voltage control or WLED current control. The reference voltage is 615 mV. Connect the feedback resistor close to this pin to minimize noise. A typical WLED backlight supply is shown in figure 8. The load current, ILOAD, is set by the selecting the external sense resistor, R1, to produce 615 mV at the desired load, for example: R1 = 0.615 ILOAD . (2) Voltage sensed across the FB pin is compared with the internal 615 mV reference to produce an error signal. The switch current is sensed by the internal sense resistor and compared to the error signal for current mode PWM control. As the error signal increases, ILOAD , increases to increase either output voltage, VOUT, or current, IOUT , such that the FB pin voltage follows the internal 615 mV reference voltage. As ILOAD is reduced, the energy required in the inductor, L1, also reduces, resulting in the inductor current dropping to zero for low load current levels. This is known as Discontinuous mode operation and results in some low-frequency ripple. The average load current will, however, remain regulated down to zero. In Discontinuous mode, when ILOAD drops to zero, the voltage at the SW pin rings, due to the resonant LC circuit formed by L1 and the switch and diode D1 capacitance. This ringing is lowfrequency and is not harmful. It can be damped with a resistor across the inductor but this will reduce efficiency and is not recommended. Device Operation The A8483 uses a 1.2 MHz constant switching frequency currentmode control scheme to regulate the output voltage or current through the load. A typical OLED bias supply is shown in figure 7. For driving OLEDs, output voltage is sensed by the FB pin through a voltage divider network. Output voltage, VOUT (V), is set according to the following equation: VOUT = R1 + R2 R2 0.615 . (1) VOUT 5 VIN VSUPPLY C1 1 F EN 4 Enable R2 39 k L1 10 H 1 SW D1 5 VIN L1 10 H 1 SW D1 VOUT OLED A8483 GND 2 FB 3 R1 820 k C2 1 F VSUPPLY C1 1 F EN 4 Enable A8483 GND 2 FB 3 R2 5 k R1 47 R3 24 k C2 0.22 F VC Analog Voltage or PWM Li-ion 2.5 V to 5.5 V Li-ion 2.5 V to 5.5 V Cf 0.01 F Figure 7. OLED Bias Supply. Use for cell phones, MP3 players, DSCs, and PDAs. (Circuit also shown in figure 1.) Figure 8. WLED Backlighting. (Circuit also shown in figure 5.) A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 4 A8483 Dimming Control 1.2 MHz Step-up Converter for Display Bias Supply Applications Information Soft Start Output voltage rise time at power-on can be extended by using a soft start circuit, such as the one shown in figure 14 for an OLED application, and in figure 16 for a WLED application. At poweron, the device duty cycle begins initially at a high level, drawing a large current from the input supply, VIN. The soft-start circuits shown can reduce the level of current flow by controlling the FB pin. When a signal is applied to the EN pin, capacitor C3 discharges, pulling the FB pin high, and reducing VOUT to a minimum. When the EN signal is removed, C3 recharges and as it does, the voltage drop across R3 reduces, allowing the device duty cycle to VOUT 5 VIN VSUPPLY Li-ion 2.5 V to 5.5 V C1 1 F EN 4 Enable R3 160 k R2 47 k L1 10 H 1 SW D1 R1 560 k FB 3 Cf 1 nF C2 1 F OLED Cf for PWM dimming only VC VOUT 5 VIN VSUPPLY C1 1 F EN 4 Enable R3 47 k VC Q1 R2 47 k L1 10 H 1 SW D1 R1 560 k FB 3 Cf 1 nF C2 10 F OLED C2 0.22 F R2 80 VOUT 5 VIN VSUPPLY Li-ion 2.5 V to 5.5 V C1 1 F EN 4 Enable R1 80 Q1 L1 10 H 1 SW D1 FB 3 VC Display dimming can be achieved by controlling the output voltage, VOUT , using the FB pin. The circuitry behind the FB pin is flexible, to accommodate a variety of schemes used for dimming: * Adjust the duty cycle of the pulse train applied to the FB pin through resistor R3, as shown in figure 11. Capacitor Cf is used to generate the average voltage level. Variation of output voltage with PWM duty cycle is shown in figure 9. * Apply a constant dc voltage to the FB pin through resistor R3, as shown in figure 12. Variation of output voltage with dc voltage are shown in figure 10. * Selection of the resistor connected between the FB pin and GND, as shown in figure 12 for OLED applications, and in figure 13 for WLED applications. The voltage drop across the transistor should be negligible compared to the FB sense voltage. 17 15 13 VOUT (V) A8483 GND 2 Analog Voltage or PWM 10 kHz 11 9 7 5 3 10 20 30 40 50 60 70 80 90 Duty Cycle (%) Figure 11. OLED Bias Supply. Use for low-noise PWM dimming, or with analog voltage through the FB pin. A8483 GND 2 Li-ion 2.5 V to 5.5 V Figure 9. PWM Dimming Control of Duty Cycle. Performance of 5 V input circuit shown in figure 3. 20 18 16 14 VOUT (V) Figure 12. OLED Dimming Control. Single-bit resolution using external transistor. 12 10 8 6 4 2 0 0.2 0.4 0.6 VC (V) 0.8 1 A8483 GND 2 Figure 10. DC Voltage Dimming Control of Duty Cycle. Performance of circuit shown in figure 11. Figure 13. WLED Dimming Control. Single-bit resolution using external transistor. Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 A8483-DS, Rev. 1 A8483 1.2 MHz Step-up Converter for Display Bias Supply increase gradually. When the voltage drop across R3 is reduced to less than about 0.8 V, the feedback from the sense resistor, R1, takes over full control of the output voltage. The length of the soft start delay depends on the combined effect of R2, R3, R4, C3 and the amplitude of the EN signal. The delay can be adjusted by the selection of these values. VOUT 5 VIN VSUPPLY Li-ion 2.5 V to 5.5 V C1 1 F EN 4 L1 10 H 1 SW D1 R1 820 k OLED FB 3 D2 Enable R4 47 k C3 10 nF R3 24 k R2 39 k A8483 GND 2 C2 1 F Component Selection The component values shown in figure 1 are sufficient for most applications. To reduce output ripple, the value of the output inductor, L1, may be increased, but in most cases this results in excessive board area and additional cost. Inductor Selection (L1). With an internal PWM frequency of Figure 14. OLED Soft Start Circuit EN VOUT 1.2 MHz, the optimum inductor value for most cases would be 10 H. The inductor should have low winding resistance, typically < 1 , and the core should have low losses at 1.2 MHz. For worst-case conditions of high output voltage and current, and low input voltage, the inductor should be rated at the switch current limit of 350 mA. If high temperature operation is required, derating should be considered. In some cases where lower inductor currents are expected, the current rating can be decreased. Several inductor manufacturers, including Coilcraft, Murata, Panasonic, Sumida, Taiyo Yuden, and TDK, have and are developing suitably small-size inductors. Two recommended inductors are: * TDK: NLCV32T-100K-PF, 10 H * Toko: 1098AS-100M, 10 H Diode Selection (D1). The diode should have a low forward volt- IIN Figure 15. OLED Soft Start Circuit. Performance of circuit shown in figure 14. VOUT 5 VIN VSUPPLY C1 1 F EN 4 L1 22 H 1 SW D1 A8483 GND 2 FB 3 D2 R2 5 k C2 0.22 F Li-ion 2.5 V to 5.5 V Enable R4 47 k C3 0.01 F R3 24 k R1 4.75 age to reduce conduction losses, and a low capacitance to reduce switching losses. Schottky diodes can provide both these features if carefully selected. The forward voltage drop is a natural advantage for Schottky diodes, and it reduces as the current rating of the component increases. However, as the current rating increases, the diode capacitance also increases, so the optimum selection is usually the lowest current rating above the circuit maximum. In this application, an average current rating of 100 to 200 mA is usually sufficient. Capacitor Selection. Because the values recommended for the Figure 16. WLED Soft Start Circuit C1. A 1.0 F capacitor on the VIN pin is suitable for most applications. In cases where large inductor currents are switched, a larger capacitor may be needed. C2. The output capacitor can be as small as 0.22 F for most applications and most VIN / VOUT combinations. Increasing this capacitor value aids in reducing ripple and increasing efficiency in low input voltage / high output voltage conditions. Suitable capacitors are available from: TDK, Taiyo Yuden, Murata, Kemet, and AVX. capacitors are low, ceramic capacitors are the best choice for this application. To reduce performance variation over temperature changes, low drift types such as X7R and X5R should be used. A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 6 A8483 1.2 MHz Step-up Converter for Display Bias Supply IOUT1 + IOUT2 = 15 mA 5 VIN VSUPPLY C1 1 F EN 4 Enable R2 39 k D2 L1 10 H Line Regulation 1 SW D1 R1 732 k FB 3 VOUT2 -12 V VOUT1 +12 V 13.0 12.8 12.6 12.4 A8483 GND 2 C2 0.47 F C3 0.47 F VOUT1 Li-ion 2.5 V to 5.5 V VOUT (V) 12.2 12.0 11.8 11.6 11.4 11.2 11.0 2.5 3.5 4.5 5.5 VOUT2 C4 0.47 F VIN (V) Figure 17. Line Regulation Perfomance for Small LCD Bias Supply, IOUT1 = IOUT2 = 7.5 mA (circuit also shown in figure 2) VOUT 5 VIN VSUPPLY C1 1 F 5V EN 4 Enable R2 15 k L1 10 H 1 SW D1 32 V, 18 mA 25 V, 25 mA 34 32 Load Regulation VOUT (V) A8483 GND 2 FB 3 R1 768 k for VOUT = 32 V 604 k for VOUT = 25 V 30 VOUT = 32 V C2 1 / 50 V F 28 26 24 22 20 0 10 20 30 40 VOUT = 25 V IOUT (mA) Figure 18.Load Regulation for LCD TV, Plasma TV Bias, FED Display, Varactor Diode Bias; VSUPPLY = 5 V (circuit also shown in figure 3) Connect either VZ or VBIAS VZ 7.5 V VSUPPLY 12 V C1 1 F VBIAS 5V 5 VIN EN 4 Enable C3 0.1 F L1 22 H 1 SW D1 VOUT 32 V, 40 mA 25 V, 80 mA 34 32 Load Regulation C2 1 / 50 V F VOUT (V) A8483 GND 2 FB 3 R1 768 k for VOUT = 32 V 604 k for VOUT = 25 V R2 15 k 30 28 26 24 22 20 0 20 40 VOUT = 32 V VOUT = 25 V 60 80 100 IOUT (mA) Figure 19. Load Regulation for LCD TV, Plasma TV Bias, FED Display, Varactor Diode Bias; VSUPPLY = 12 V (circuit also shown in figure 4). The A8483 can operate with a VSUPPLY from 0.9 to 18 V with a separate bias supply to operate the A8483 in the normal VIN range. The bias voltage can be supplied by an external power supply, such as 3.3 or 5 V, or by using a suitable Zener diode, VZ , for VSUPPLY > 10 V. A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 7 A8483 1.2 MHz Step-up Converter for Display Bias Supply Use the following complete part number when ordering: Part Number A8483EEKTR-T Packing 7-in. reel, 1500 pieces/reel Description Surface Mount Leadframe plating 100% matte-tin. Solder pad layout compatible with SOT23-5 (SOT95P280-5). Package EK , MLP/TDFN 3.15 .124 2.85 .112 Preliminary dimensions, for reference only (reference JEDEC MO-229 WEEA) Dimensions in millimeters U.S. Customary dimensions (in.) in brackets, for reference only Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Exposed thermal pad (reference dimensions only, terminal #1 identifier appearance at supplier discretion) C Reference pad layout (reference IPC SON95P300X310-7WEEAN); adjust as necessary to meet application process requirements D Reference pad layout with contact pads only; adjust as necessary to meet application process requirements 5X 0.08 [.003] C 5X 0.45 .018 0.30 .012 0.10 [.004] M C A B 0.05 [.002] M C 0.95 .037 0.50 .020 0.30 .012 1 A 5 A B 3.15 .124 2.85 .112 2 C SEATING PLANE 0.80 .031 0.70 .028 0.20 .008 REF 0.05 .002 0.00 .000 1 2 R0.20 .008 REF B 1.00 .039 NOM 5 2.00 .079 NOM 2.00 .079 MAX 0.45 .018 MIN 0.85 .033 MIN 5 0.45 .018 MIN 0.85 .033 MIN 0.45 .018 MIN 5 2.10 .083 MIN 3.80 .150 MAX 0.20 x 0.20 .008 x .008 REF 1.00 MAX .039 2.10 .083 MIN 3.80 .150 MAX 1 D 0.95 .037 0.50 .020 MIN 1 C 0.95 .037 0.50 .020 MIN A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 8 A8483 1.2 MHz Step-up Converter for Display Bias Supply The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. Copyright(c) 2005 AllegroMicrosystems, Inc. A8483-DS, Rev. 1 Allegro MicroSystems, Inc. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 9 |
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