AP1538 18V 3A 300KHz BUCK CONVERTER General Description Features • • • • • • • • • • 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. 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) Applications • • • • • • • • PC Motherboard LCD Monitor Graphic Card DVD-Video Player Telecom Equipment ADSL Modem Printer and other Peripheral Equipment Microprocessor core supply Typical Application Circuit Vcc VIN Output ROCSET COCSET 3K Option C IN OCSET 470uF CVcc 0.1uF R EN 100K 22uH Cc AP 1538 EN VOUT = 5V/3A L1 Option* RA 6.8K + FB V SS D1** C + 0.1uF - COUT 470uF*** RB 1.3K C EN 0.1uF VOUT = V FB x (1+ R A /RB ) R B= 0.7K~5K ohm Notes: AP1538 Rev. 5 DS31451 * Typical feedback compensation (Cc): 5600pF. ** Suggested DIODES Power Schottky P/N: B540 series or PDS540. *** Suggested COUT for VOUT < 1V; 680uF. 1 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Ordering Information AP 1538 XXX G - 13 Device Package Green Packing S : SOP-8L SDP : SOP-8L-DEP G : Green 13 : Tape & Reel Package Code Packaging (Note 2) S SDP SOP-8L SOP-8L-DEP AP1538SG-13 AP1538SDPG-13 Notes: 13” Tape and Reel Quantity Part Number Suffix 2500/Tape & Reel 2500/Tape & Reel -13 -13 1. EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at http://www.diodes.com/products/lead_free.html 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. Pin Assignments (1) SOP-8L (2) SOP-8L-DEP (Dual Exposed Pads) ( Top View ) ( Top View ) 8 Vss EN 2 7 Vss Output OCSET 3 6 Output Output VCC 4 5 Output Vss FB 1 8 EN 2 7 Vss OCSET 3 6 VCC 4 5 FB 1 1 2 Notes: (Note 3) 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. AP1538 Rev. 5 DS31451 2 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Pin Descriptions Pin Name Pin No. Description FB 1 Feedback pin EN 2 Power-off pin H: Normal operation (Step-down operation) L: Step-down operation stopped (All circuits deactivated) OCSET 3 Add an external resistor to set max output current VCC 4 IC power supply pin Output 5, 6 Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin to reduce EMI VSS 7, 8 GND Pin Block Diagram Output Oscillation Circuit Reference Voltage Source with Soft Start Vcc + PWM-Switched Control Circuit FB - Thermal Shutdown VEN EN AP1538 Rev. 5 DS31451 3 of 13 www.diodes.com 90uA Vss OCSET OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Absolute Maximum Ratings Symbol Parameter Rating Unit ESD HBM Human Body Model ESD Protection 5.5 KV ESD MM Machine Model ESD Protection 200 V VSS - 0.3 to VSS + 20 V VCC VCC Pin Voltage VFB Feedback Pin Voltage VSS - 0.3 to VCC V VEN EN Pin Voltage VSS - 0.3 to VCC V VOUT Switch Pin Voltage VSS - 0.3 to VCC V PD Power Dissipation Internally limited mW TJ Operating Junction Temperature Range TST Storage Temperature Range -40 to +125 o C -65 to +150 o 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. 5 DS31451 4 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Electrical Characteristics (VIN = 12V, TA = 25°C, 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) Min 0.784 - Typ. 0.8 0.1 Max 0.816 0.5 Unit V µA - 10 - µA VIN = 5V~18V - 1 2 % IOUT = 0.1 to 3A - 0.2 0.5 % Measure waveform at SW pin 240 300 400 KHz Measure waveform at SW pin - 50 - KHz 2.0 75 - 20 -10 90 110 70 0.8 105 - - 92 - % - 150 55 24 26 - °C °C 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 EFFI Efficiency TSHDN THYS Thermal shutdown threshold Thermal shutdown hysteresis SOP-8L (Note 5) Thermal Resistance Junction-to-Case SOP-8L-DEP (Note 5) θJC Notes: V µA µA µA mΩ o 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. 5 DS31451 5 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Typical Performance Characteristics 326 VIN vs. Frequency VIN vs. VFB (V OUT = 3.3V, IOUT = 0.2A) (V OUT = 3.3V, IOUT = 0.2A) 0.820 324 322 0.815 0.810 320 318 V FB (V) FOSC (kHz) 0.805 0.800 316 314 0.795 312 310 0.790 0.785 308 306 0.780 0 2 4 6 8 10 V IN (V) 12 14 16 0 18 2 Line Regulation 3.35 3.30 V OUT (V) V OUT (V) 3.25 3.20 3.15 3.10 3.05 3.00 0 2 4 6 8 10 V IN (V) 12 14 16 18 0.0 0.5 6.5 70 6.0 Current Limit (A) 7.0 80 60 50 40 30 20 VOUT=3.3V 10 VOUT=5V 14 16 18 1.5 IOUT (A) 2.0 2.5 3.0 (TA = 25C) 2.0 5.5 5.0 4.5 4.0 3.5 ROCSET=6.8k 3.0 ROCSET=3.9k 2.5 3.0 IOUT (A) AP1538 Rev. 5 DS31451 1.0 7.5 1.0 12 Switch Current Limit (V IN = 12V) 90 0 0.0 8 10 V IN (V) (V IN = 12V) 3.35 3.34 3.33 3.32 3.31 3.30 3.29 3.28 3.27 3.26 3.25 Efficiency 100 6 Load Regulation (V OUT = 3.3V, IOUT = 0.2A) 3.40 Efficiency (%) 4 6 of 13 www.diodes.com 0 2 4 6 8 10 V IN (V) 12 14 16 18 OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Typical Performance Characteristics (Continued) Current Limit (A) Current Limit vs. Temperature (V IN=12V, ROCSET =6.8k) 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 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. 5 DS31451 7 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Test Circuit VCC OUTPUT Oscillation open open FB OCSET A EN + - VSS Enable function test VCC + - A OUTPUT VCC OUTPUT OCSET EN FB VSS Feedback function test FB OCSET EN + VSS V - Operation function test AP1538 Rev. 5 DS31451 8 of 13 www.diodes.com OCTOBER 2009 © 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 Inductor Selection For most designs, the operates with inductors of 22µH to 33µH. The inductor value can be derived from the following equation: 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. Where ΔIL 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). 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: IPEAK × R DS(ON) = IOCSET × R OCSET VIN − VOUT VOUT × fs × ΔI VIN 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 1⁄2 the DC load current. A low ESR input capacitor sized for maximum RMS current must be used. A 470µF 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. (ΔI) IPEAK > IOUT(MAX) + 2 where, ΔI = L= VIN − VOUT VOUT × fs × L VIN V RIPPLE = ΔIL × ESR 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 ΔI. The above equation is recommended for input voltage range of 5V to 18V. For input voltage lower than 5V or ambient temperature over 100°C, higher ROCSET is recommended. 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. The recommended minimum ROCSET value is summarized below: VOUT (V) 0.8 1.0 1.2 1.8 2.5 3.3 5.0 5V 4.7K 5.6K 5.6K 5.6K 5.6K 5.6K N/A AP1538 Rev. 5 DS31451 VIN (V) 12V 3.0K 3.0K 3.0K 3.0K 3.0K 3.0K 3.0K 18V 3.3K 3.9K 3.9K 3.9K 3.9K 3.9K 4.7K 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. 9 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Functional Description (Continued) Keep the gap of exposed pads from short circuit. Recommended exposed-pads gap: 30~40mil (0.75~1mm) Top Side Layout Guide 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. Brown: IC exposed pads. Red: recommended layout. Reference pads layout dimension: Output: 90 x 50 mil Vss: 90 x 60 mil Bottom Side Layout Guide AP1538 Rev. 5 DS31451 10 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Functional Description (Continued) Vcc VIN Output C7 Option R4 C2 C1 Option AP1538 VOUT R1 + FB OCSET V SS EN C3 L1 R5 D1 C8 + C4 - R2 C6 Figure: Layout numbering comparison. Marking Information (1) SOP-8L ( Top View ) 8 5 Logo Part Number AP1538 YY WW X X 1 G : Green YY : Year : 08, 09,10~ WW : Week : 01~52; 52 represents 52 and 53 week X : Internal Code 4 (2) SOP-8L-DEP ( Top View ) 8 5 Logo Part No. AP1538 YY WW X X E 1 AP1538 Rev. 5 DS31451 G : Green YY : Year : 08, 09,10~ WW : Week : 01~52; 52 represents 52 and 53 week X : Internal Code SOP-8L-DEP 4 11 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER Package Information ( All Dimensions in mm ) 0.254 0.10/0.20 3.85/3.95 5.90/6.10 (1) Package type: SOP-8L Gauge Plane Seating Plane 0.62/0.82 Detail "A" 7°~9° 7°~9° 0.15/0.25 1.75max. 1.30/1.50 0.35max. 45° Detail "A" 0°/8° 0.3/0.5 1.27typ 4.85/4.95 5.4 8x-0.60 8x-1.55 6x-1.27 Land Pattern Recommendation (Unit: mm) (2) Package type: SOP-8L-DEP CL 1.8 1.65 1.8 0.95 8 5 8x-1.55 8 EXPOSED PAD 1.0 2.35 5.4 3.85/3.95 5.90/6.10 5 CL Top View 4 1 0.35Typ. 0.254 0.15/0.25 1.15Typ. 2.05Typ. 0 °/ View"A" 1.27Typ. 4.85/4.95 8° 1.63Max. 1.4/1.5 .1 0.685 6x-1.27 8x-0.60 45° R0 4 1 0.3/0.5 9°(all side) 4 1 Gauge Plane Seating Plane EXPOSED PAD 0.9 8 CL 0.62/0.82 0/0.13 0.20 2.15Typ. Land Pattem Recommendation (Unit: mm) View"A" 5 1.7 1.7 0.713 CL Bottom view AP1538 Rev. 5 DS31451 12 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated AP1538 18V 3A 300KHz BUCK CONVERTER IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. 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Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks. LIFE SUPPORT Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright © 2009, Diodes Incorporated www.diodes.com AP1538 Rev. 5 DS31451 13 of 13 www.diodes.com OCTOBER 2009 © Diodes Incorporated