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| AP1538 18V 3A 300KHz BUCK CONVERTER Features * * * * * * * * * * Input voltage : 3.6V to 18V Output voltage : 0.8V to VCC Output current : up to 3A Duty ratio: 0% to 99% PWM control Oscillation frequency: 300KHz typical Soft-start like, Current limit and Enable function Thermal Shutdown function Built-in internal SW P-channel MOS SOP-8L and SOP-8L-DEP: Available in "Green" Molding Compound (No Br, Sb) Lead Free Finish / RoHS Compliant (Note 1) General Description AP1538 consists of step-down switching regulator with PWM control. These devices include a reference voltage source, oscillation circuit, error amplifier, internal PMOS. AP1538 provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to vary the duty ratio linearly from 0 up to 99%. This converter also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. An enable function, an over current protect function and a short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced from 300KHz to 50KHz. Also, an internal compensation block is built in to minimum external component count. With the addition of an internal P-channel Power MOS, a coil, capacitors, and a diode connected externally, these ICs can function as step-down switching regulators. They serve as ideal power supply units for portable devices when coupled with the SOP-8L and SOP-8L-DEP mini-packages, providing such outstanding features as low current consumption. Since this converter can accommodate an input voltage up to 18V, it is also suitable for the operation via an AC adapter. Applications * * * * * * * * PC Motherboard LCD Monitor Graphic Card DVD-Video Player Telecom Equipment ADSL Modem Printer and other Peripheral Equipment Microprocessor core supply Ordering Information AP 1538 XXX G - X Package S : SOP-8L SDP : SOP-8L-DEP Package Code S S SDP SDP Packaging (Note 2) SOP-8L SOP-8L SOP-8L-DEP SOP-8L-DEP Lead Free G : Green Packing U : Tube 13 : Tape & Reel Tube Quantity Part Number Suffix 100 -U NA NA 100 -U NA NA 13" Tape and Reel Quantity Part Number Suffix NA NA 2500/Tape & Reel -13 NA NA 2500/Tape & Reel -13 Device AP1538SG-U AP1538SG-13 AP1538SDPG-U AP1538SDPG-13 Notes: 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied, see EU Directive 2002/95/EC Annex Notes. 2. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. AP1538 Rev. 2 1 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Pin Assignments (1) SOP-8L (2) SOP-8L-DEP (Dual Exposed Pads) ( Top View ) Vss Vss Output Output FB 1 ( Top View ) Vss Vss Output Output FB 1 EN 2 OCSET 3 VCC 4 8 7 6 5 8 1 EN 2 OCSET 3 7 6 2 VCC 4 (Note 3) 5 Notes: 3. Exposed pad 1 is connected to VSS and exposed pad 2 is connected to Output. The board layout for exposed pads needs to be considered to avoid short circuit. Pin Descriptions Pin Name FB Pin No. 1 Description Feedback pin Power-off pin H: Normal operation (Step-down operation) L: Step-down operation stopped (All circuits deactivated) Add an external resistor to set max output current IC power supply pin Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin to reduce EMI GND Pin EN 2 OCSET VCC Output VSS 3 4 5, 6 7, 8 AP1538 Rev. 2 2 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Block Diagram Output Oscillation Circuit Vcc PWM-Switched Control Circuit Thermal Shutdown VEN 90uA Vss + Reference Voltage Source with Soft Start FB - EN OCSET Absolute Maximum Ratings Symbol ESD HBM ESD MM VCC VFB VEN VOUT PD TJ TST Parameter Human Body Model ESD Protection Machine Model ESD Protection VCC Pin Voltage Feedback Pin Voltage EN Pin Voltage Switch Pin Voltage Power Dissipation Operating Junction Temperature Range Storage Temperature Range Rating 7 450 VSS - 0.3 to VSS + 20 VSS - 0.3 to VCC VSS - 0.3 to VCC VSS - 0.3 to VCC Internally limited -40 to +125 -65 to +150 Unit KV V V V V V mW o o C C Caution: The absolute maximum ratings are rated values exceeding which the product could suffer physical damage. These values must therefore not be exceeded under any conditions. Recommended Operating Conditions Symbol VIN IOUT TA Notes: Parameter Input Voltage (Note 4) Output Current Operating Ambient Temperature Min 3.6 0 -20 Max 18 3 +85 Unit V A o C 4. For the operations in low input voltage, AP1538 can tolerate down to 3.6V but max output current loading will be less than 3A. For nominal applications in such low input voltage range, especially lower than 4V, a higher ROCSET with larger heat sink is recommended. AP1538 Rev. 2 3 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Electrical Characteristics (VIN = 12V, TA = 25C, unless otherwise specified) Symbol Parameter Conditions VFB Feedback Voltage IOUT = 0.1A IFB Feedback Bias Current IOUT = 0.1A Current Consumption During ISHDN VEN = 0V Power Off VOUT Line Regulation / VIN VOUT Load Regulation / VOUT fOSC Oscillation Frequency Frequency of Current Limit or fOSC1 Short Circuit Protection VIH EN Pin Input Voltage VIL ISH EN Pin Input Leakage Current ISL IOCSET OCSET Pin Bias Current RDS(ON) Internal MOSFET RDS(ON) EFFI TSHDN THYS JC Notes: Min 0.784 240 2.0 75 - Typ. 0.8 0.1 10 1 0.2 300 50 20 -10 90 110 70 92 150 55 24 26 Max 0.816 0.5 2 0.5 400 0.8 105 - Unit V A A % % KHz KHz V A A A m % C C o VIN = 5V~18V IOUT = 0.1 to 3A Measure waveform at SW pin Measure waveform at SW pin Evaluate oscillation at SW pin Evaluate oscillation stop at SW pin EN Pin High EN Pin Low -VIN=5V, VFB=0V VIN=12V, VFB=0V VIN=12V, VOUT = 5V IOUT=3A Efficiency Thermal shutdown threshold Thermal shutdown hysteresis SOP-8L (Note 5) Thermal Resistance Junction-to-Case SOP-8L-DEP (Note 5) C/W 5. Test condition for SOP-8L and SOP-8L-DEP: Devices mounted on 2oz copper, minimum recommended pad layout on top & bottom layer with thermal vias, double sided FR-4 PCB. AP1538 Rev. 2 4 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Typical Application Circuit VOUT = 5V/3A RA 6.8K VIN ROCSET COCSET Option 3K C IN 470uF CVcc 0.1uF R EN 100K C EN 0.1uF Vcc Output L1 22uH Cc Option (Note 8) AP 1538 OCSET EN FB V SS + C + COUT 470uF (Note 7) - 0.1uF D1 (Note 6) RB 1.3K VOUT =V FB x (1+ R A /RB ) R B = 0.7K~5 K ohm Notes: 6. Suggested DIODES Power Schottky P/N: B340 series or PDS340. 7. Suggested COUT for VOUT < 1V; 680F. 8. Typical feedback compensation (Cc): 5600pF. AP1538 Rev. 2 5 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Typical Performance Characteristics VIN vs. Frequency 326 324 322 (V OUT = 3.3V, IOUT = 0.2A) 0.820 0.815 0.810 VIN vs. VFB (V OUT = 3.3V, IOUT = 0.2A) FOSC (kHz) 316 314 312 310 308 306 0 2 4 6 8 10 V IN (V) 12 14 16 18 V FB (V) 320 318 0.805 0.800 0.795 0.790 0.785 0.780 0 2 4 6 8 10 V IN (V) 12 14 16 18 Line Regulation 3.40 3.35 3.30 (V OUT = 3.3V, IOUT = 0.2A) 3.35 3.34 3.33 3.32 3.31 3.30 3.29 3.28 3.27 3.26 3.25 0.0 0.5 Load Regulation (V IN = 12V) V OUT (V) 3.20 3.15 3.10 3.05 3.00 0 2 4 6 8 10 V IN (V) 12 14 16 18 V OUT (V) 3.25 1.0 1.5 IOUT (A) 2.0 2.5 3.0 Efficiency 100 90 80 60 50 40 30 20 10 0 0.0 1.0 IOUT (A) 2.0 VOUT=3.3V VOUT=5V 3.0 70 (V IN = 12V) 7.5 7.0 6.5 Switch Current Limit (TA = 25C) Current Limit (A) Efficiency (%) 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 0 2 4 6 8 10 V IN (V) 12 14 16 18 ROCSET=6.8k ROCSET=3.9k AP1538 Rev. 2 6 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Typical Performance Characteristics Current Limit vs. Temperature 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 -25 0 25 50 75 Ambient Temperature (C) 100 (V IN=12V, ROCSET =6.8k) (Continued) Current Limit (A) VOUT Ripple (VIN = 12V, VOUT = 3.3V, IOUT = 0.1A) VOUT Ripple (VIN = 12V, VOUT = 3.3V, IOUT = 3.0A) Load Transient Response (VIN = 12V, VOUT = 3.3V, IOUT = 0.1~3A) AP1538 Rev. 2 7 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Test Circuit Oscillation open VCC OUTPUT FB open A VCC OUTPUT FB OCSET A + EN VSS - OCSET EN VSS Enable function test Feedback function test VCC + - OUTPUT FB OCSET EN VSS + V Operation function test AP1538 Rev. 2 8 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Functional Description PWM Control The AP1538 is a DC/DC converter that employs pulse width modulation (PWM) scheme. Its pulse width varies in the range of 0% to 99%, based on the output current loading. The output ripple voltage caused by the PWM high frequency switching can easily be reduced through an output filter. Therefore, this converter provides a low ripple output supply over a broad range of input voltage & output current loading Under Voltage Lockout The under voltage lockout circuit of the AP1538 assures that the high-side MOSFET driver remains in the off state whenever the supply voltage drops below 3.3V. Normal operation resumes once VCC rises above 3.5V. Current Limit Protection The current limit threshold is set by external resistor ROCSET connected from VCC supply to OCSET pin. The internal sink current IOCSET (90uA typical) across this resistor sets the voltage at OCSET pin. When the PWM voltage is less than the voltage at OCSET, an over-current condition is triggered. The current limit threshold is given by the following equation: Inductor Selection For most designs, the operates with inductors of 22H to 33H. The inductor value can be derived from the following equation: L= (VIN - VOUT )TON 2 x I L x f osc Where IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple current. Choose inductor ripple current approximately 15% of the maximum load current 3A, IL=0.45A. The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (3A+0.225A). Input Capacitor Selection This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage. The RMS current rating requirement for the input capacitor of a buck regulator is approximately 12 the DC load current. A low ESR input capacitor sized for maximum RMS current must be used. A 470F low ESR capacitor for most applications is sufficient. Output Capacitor Selection The output capacitor is required to filter the output voltage and provides regulator loop stability. The important capacitor parameters are the 100KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating and capacitance value. For the output capacitor, the ESR value is the most important parameter. The output ripple can be calculated from the following formula. IPEAK x RDS(ON) = IOCSET x ROCSET IPEAK > IOUT (MAX) + 2 where, ( I) I = VIN - VOUT VOUT x FS x L VIN VRIPPLE = IL x ESR The bulk capacitor's ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient. An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings may be needed to provide the low ESR values required for low output ripple voltage. PCB Layout Guide If you need low TC & TJ or large PD (Power Dissipation), The dual SW pins(5& 6) and Vss pins(7& 8)on the SOP-8L package are internally connected to die pad, The evaluation board should be allowed for maximum copper area at output (SW) pins. 1. Connect FB circuits (R1, R2, C1) as closely as possible and keep away from inductor flux for pure VFB. 2. Connect C3 to Vcc and Vss pin as closely as possible to get good power filter effect. 3. Connect R4 to Vcc and OCSET pin as closely as possible. 4. Connect ground side of the C2 & D1 & C4 as closely as possible and use ground plane for best performance. IPEAK is the output peak current; RDS (ON) is the MOSFET ON resistance; FS is the PWM frequency (300KHz typical). Also, the inductor value will affect the ripple current I. The above equation is recommended for input voltage range of 5V to 18V. For input voltage lower than 5V or ambient temperature over 100C, higher ROCSET is recommended. The recommended minimum ROCSET value is summarized below: VOUT (V) 0.8 1.0 1.2 1.8 2.5 3.3 5.0 VIN (V) 12V 3.0K 3.0K 3.0K 3.0K 3.0K 3.0K 3.0K 5V 4.7K 5.6K 5.6K 5.6K 5.6K 5.6K N/A 18V 3.3K 3.9K 3.9K 3.9K 3.9K 3.9K 4.7K AP1538 Rev. 2 9 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Functional Description (Continued) Keep the gap of exposed pads from short circuit. Top Side Layout Guide Recommended exposed-pads gap: 30~40mil (0.75~1mm) Use vias to conduct the heat into the backside of PCB layer. The heat sink at output (SW) pins should be allowed for maximum solder-painted area. Bottom Side Layout Guide Brown: IC exposed pads. Red: recommended layout. AP1538 Rev. 2 10 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Functional Description (Continued) VIN R4 C2 R5 C6 C7 Option Vcc Output L1 VOUT R1 AP1538 OCSET EN V SS FB C1 Option + - C8 + - C4 C3 D1 R2 Figure: Layout numbering comparison. AP1538 Rev. 2 11 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Marking Information (1) SOP-8L ( Top View ) 8 5 Logo Part No. AP1538 YYWW X X 1 4 G : Green Internal code Xth week: 01~52 Year : "07" = 2007 "08" = 2008 ~ SOP-8L (2) SOP-8L-DEP ( Top View ) 8 5 Logo Part No. AP1538 YYWW X X E 1 4 G : Green E : SOP-8L-DEP Internal code Xth week: 01~52 Year : "07" = 2007 "08" = 2008 ~ SOP-8L-DEP AP1538 Rev. 2 12 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Package Information (1) SOP-8L ( All Dimensions in mm ) 3.70/4.10 5.79/6.20 0.08/0.25 0.254 0.38/1.27 Gauge Plane Seating Plane Detail "A" 7~9 1.30/1.50 1.75max. 0.20typ 0.35max. 45 7~9 Detail "A" 3.70/4.10 1.27typ 4.80/5.30 0.3/0.5 0.78 8x-0.41 5.1 6x-1.27 8x-1.0 Land Pattern Recommendation (Unit: mm) (2) SOP-8L-DEP 1.8 1.65 8 8 5 C L 1.8 0.95 8x-1.55 EXPOSED PAD 5 3.85/3.95 5.90/6.10 5.4 2.35 1.0 C L Top View 1 4 0.3/0.5 9(all side) 1 4 Land Pattem Recommendation (Unit: mm) 0.35Typ. 45 8x-0.60 6x-1.27 1.63Max. 1.4/1.5 4.85/4.95 0.685 2.05Typ. 1 4 EXPOSED PAD 0.254 Gauge Plane Seating Plane 1.15Typ. 2.15Typ. 0.9 C L 0/0.13 0.20 0.15/0.25 R0 .1 1.27Typ. View"A" 0.62/0.82 View"A" 8 5 1.7 C L 1.7 0.713 Bottom view AP1538 Rev. 2 13 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER IMPORTANT NOTICE Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to any product herein. Diodes Incorporated does not assume any liability arising out of the application or use of any product described herein; neither does it convey any license under its patent rights, nor the rights of others. The user of products in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on our website, harmless against all damages. LIFE SUPPORT Diodes Incorporated products are not authorized for use as critical components in life support devices or systems without the expressed written approval of the President of Diodes Incorporated. AP1538 Rev. 2 14 of 14 www.diodes.com JUNE 2008 (c) Diodes Incorporated |
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