AP5100W

AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Description The AP5100 is a current mode step-down converter with a built-in power MOSFET to enable smallest solution size power conversion. BST Pin Assignments ( Top View ) 1 2 3 SOT26 6 5 7 4 SW IN EN With the low series resistance power switch it enables a constant output current of up to 1.2A over a wide input supply range. The load and line regulation has excellent response time over the operating input voltage and temperature range. The AP5100 is self protected, through a cycle-by-cycle current limiting algorithm and an on chip thermal protection. The AP5100 will provide the voltage conversion with a low count of widely available standard external components. The AP5100 is available in SOT26 package. GND FB Features • • • • • • • • • • • • VIN 4.75V to 24V Load current of up to 1.2A Internal Power MOSFET Stable with Low ESR Ceramic Output Capacitors Up to 90% Efficiency 0.1µA Shutdown Mode Fixed 1.4MHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Resistor divider adjustable Output: 0.81V to 15V SOT26: Available in “Green” Molding Compound (No Br, Sb) Lead Free Finish/RoHS Compliant (Note 1) Applications • • • • Distributed Power Systems Battery Charger Pre-Regulator for Linear Regulators WLED Drivers Notes: 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. Typical Application Circuit VIN C1 5 IN BST 1 C3 .1 L VOUT D1 R1 C6 C2 R2 FB 3 AP5100 ON OFF 4 EN SW 6 GND Figure 1. Efficiency vs. Load Current Figure 2. Typical Application Circuit 1 of 10 www.diodes.com AP5100 Document number: DS32130 Rev. 2 - 2 November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Typical Application Circuit (continiued) VIN C1 10µF 25V R3 100kohm 4 5 IN BST 1 6 C3 22nF D1 B230A L1 3.3µH R1 49.9kohm R2 16.2kohm C6 100pF AP5100 SW VOUT 3.3V C2 22µF 6.3V OFF ON EN GND FB 3 Figure 3. 1.4MHz, 3.3V Output at 1A Step-Down Converter VIN 6V -12V C1 10µF 25V R3 100Kohm 5 IN BST 1 6 C3 10nF AP5100 SW D1 - Vout L1 10µH C2 10µF 16V LED1 1N5819HW-7 - Vout OFF ON 4 EN - Vout GND FB 3 LED 2 R4 200Kohm 1% R2 40 ohm 1% - Vout LED 3 Figure 4. White LED Driver Application AP5100 Document number: DS32130 Rev. 2 - 2 2 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Pin Descriptions Pin Name BST GND FB Pin # 1 2 3 Description Bootstrap. To form a boost circuit, a capacitor is connected between SW and BST pins to form a floating supply across the power switch driver. This capacitor is needed to drive the power switch’s gate above the supply voltage. Typical values for CBST range from 0.1uF to 1uF. Ground. This pin is the voltage reference for the regulated output voltage. All control circuits are referenced to this pin. For this reason care must be taken in its layout. Feedback. To set the output voltage, connect this pin to the output resistor divider or directly to VOUT. To prevent current limit run away during a current limit condition, the frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 400mV. On/Off Control Input. Do not leave this pin floating. To turn the device ON, pull EN above 1.2V and to turn it off pull below 0.4V. If enable/disable is not used, connect a 100kOhm resistor between EN to VIN. Supply Voltage. The AP5100 operates from a +4.75V to +24V unregulated input. A decoupling capacitor C1 is required to prevent large voltage spikes from appearing at the input. Place this capacitor near the IC. Switch Output. This is the reference for the floating top gate driver. EN 4 IN SW 5 6 Functional Block Diagram Figure 5. Functional Block Diagram AP5100 Document number: DS32130 Rev. 2 - 2 3 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Absolute Maximum Ratings (Note 2) Symbol ESD HBM ESD MM VIN VSW VBST TST TJ TL θJA θJC Notes: Description Human Body Model ESD Protection Machine Model ESD Protection Supply Voltage Switch Voltage Boost Voltage All Other Pins Storage Temperature Junction Temperature Lead Temperature Junction to Ambient Thermal Resistance (Note 3) Junction to Case Thermal Resistance (Note 3) Rating 3 300 26 -0.3 to VIN + 0.3 VSW + 6 –0.3 to +6 -65 to +150 +150 +260 140 35 Unit KV V V V V V °C °C °C °C/W °C/W 2. Exceeding these ratings may damage the device. 3. Test condition for SOT26: Measured on approximately 1” square of 1 oz copper. Recommended Operating Conditions (Note 4) Symbol VIN TA VOUT Note: Description Supply Voltage Operating Ambient Temperature Range Output Voltage Rating 4.75 to 24 -25 to +85 0.81 to 15 Unit °C °C V 4. The device function is not guaranteed outside of the recommended operating conditions. Electrical Characteristics (VIN = 12V, TA = +25°C, unless otherwise noted) Symbol VFB IFB RDS(ON) Parameter Feedback Voltage Feedback Current Switch-On Resistance (Note 5) Switch Leakage Current Limit (Note 5) Oscillator Frequency Fold-back Frequency Maximum Duty Cycle Minimum On-Time (Note 5) Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis EN Input Low Voltage EN Input High Voltage EN Input Current IS IQ Note: Test Conditions 4.75V ≤ VIN ≤ 24V VFB = 0.8V VEN = 0V, VSW = 0V VFB = 0.6V VFB = 0V VFB = 0.6V Min 0.790 Typ. 0.810 0.1 0.35 2.4 1.4 480 87 100 4.0 150 Max 0.830 10 1.1 1.7 fSW tON Unit V µA Ω µA A MHz kHz % ns V mV 3.8 4.2 0.4 1.2 VEN = 2V VEN = 0V VEN = 0V VEN = 2V, VFB = 1V 0.3 0.1 0.1 0.4 140 V V µA Supply Current (Shutdown) Supply Current (Quiescent) Thermal Shutdown (Note 5) 1.0 1.0 µA mA °C 5. Guaranteed by design. AP5100 Document number: DS32130 Rev. 2 - 2 4 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Typical Performance Characteristics VIN = 12V, VOUT = 3.3V, L = 3.3uH, C1 = 10uF, C2 = 22uF, TA = +25°C, unless otherwise noted. Steady State Test (IOUT=0.5A) Load Transient Test (IOUT=0.2A to 0.8A. Step at 0.8A/us) Time- 1us/div Start-up Through Enable (No Load) Time- 100us/div Start-up through Enable (IOUT=1A, resistive load) Time- 50us/div Shutdown Through Enable (No Load) Time- 50us/div Shutdown Through Enable (IOUT=1A, resistive load) Time- 50us/div Time- 50us/div AP5100 Document number: DS32130 Rev. 2 - 2 5 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Typical Performance Characteristics (continued) Short Circuit Entry Short Circuit Recovery Time- 50us/div Time- 100us/div Applications Information OPERATION The AP5100 is a current mode control, asynchronous buck regulator. Current mode control assures excellent line and load regulation and a wide loop bandwidth for fast response to load transients. Figure. 4 depicts the functional block diagram of AP5100. The operation of one switching cycle can be explained as follows. At the beginning of each cycle, HS (high-side) MOSFET is off. The EA output voltage is higher than the current sense amplifier output, and the current comparator’s output is low. The rising edge of the 1.4MHz oscillator clock signal sets the RS Flip-Flop. Its output turns on HS MOSFET. When the HS MOSFET is on, inductor current starts to increase. The Current Sense Amplifier senses and amplifies the inductor current. Since the current mode control is subject to sub-harmonic oscillations that peak at half the switching frequency, Ramp slope compensation is utilized. This will help to stabilize the power supply. This Ramp compensation is summed to the Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS Flip-Flop is reset and HS MOSFET is turned off. The external Schottky rectifier diode (D1) conducts the inductor current. For one whole cycle, if the sum of the Current Sense Amplifier output and the Slope Compensation signal does not exceed the EA output, then the falling edge of the oscillator clock resets the Flip-Flop. The output of the Error Amplifier increases when feedback voltage (VFB) is lower than the reference voltage of 0.81V. This also increases the inductor current as it is proportional to the EA voltage. Setting the Output Voltage The output voltage can be adjusted from 0.81V to 15V using an external resistor divider. Table 1 shows a list of resistor selection for common output voltages. Resistor R1 is selected based on a design tradeoff between efficiency and output voltage accuracy. For high values of R1 there is less current consumption in the feedback network. However the trade off is output voltage accuracy due to the bias current in the error amplifier. R2 can be determined by the following equation: ⎛V ⎞ ⎜ ⎟ R1 = R 2 × ⎜ OUT − 1⎟ 0.81 ⎝ ⎠ Equation 1 VOUT (V) 1.8 2.5 3.3 5 R1 (kΩ) 80.6 (1%) 49.9 (1%) 49.9 (1%) 49.9 (1%) R2 (kΩ) 64.9 (1%) 23.7 (1%) 16.2 (1%) 9.53 (1%) Table 1. Resistor Selection for Common Output Voltages L= VOUT × (VIN − VOUT ) VIN × ΔIL × fSW Equation 2 Where ΔIL is the inductor ripple current. And fSW is the buck converter switching frequency. AP5100 Document number: DS32130 Rev. 2 - 2 6 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Applications Information (Continued) Setting the Output Voltage (Continued) Choose the inductor ripple current to be 30% of the maximum load current. The maximum inductor peak current is calculated from: ΔI IL(MAX) = ILOAD + L 2 Equation 3 Peak current determines the required saturation current rating, which influences the size of the inductor. Saturating the inductor decreases the converter efficiency while increasing the temperatures of the inductor, the MOSFET and the diode. Hence choosing an inductor with appropriate saturation current rating is important. A 1µH to 10µH inductor with a DC current rating of at least 25% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor’s DC resistance should be less than 200mΩ. Use a larger inductance for improved efficiency under light load conditions. ESR of the output capacitor dominates the output voltage ripple. The amount of ripple can be calculated from the equation below: Vout capacitor = ΔIinductor × ESR An output capacitor with ample capacitance and low ESR is the best option. For most applications, a 22µF ceramic capacitor will be sufficient. External Diode The external diode’s forward current must not exceed the maximum output current. Since power dissipation is a critical factor when choosing a diode, it can be calculated from the equation below: V Pdiode = (1 − OUT ) × Iout × 0.3V VIN Equation 5 Note: 0.3V is the voltage drop across the schottky diode. A diode that can withstand this power dissipation must be chosen. Input Capacitor The input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. The input capacitor has to sustain the ripple current produced during the on time on the upper MOSFET. It must hence have a low ESR to minimize the losses. Due to large dI/dt through the input capacitors, electrolytic or ceramics should be used. If a tantalum must be used, it must be surge protected. Otherwise, capacitor failure could occur. For most applications, a 4.7µF ceramic capacitor is sufficient. External Bootstrap Diode It is recommended that an external bootstrap diode be added when the input voltage is no greater than 5V or the 5V rail is available in the system. This helps improve the efficiency of the regulator. The bootstrap diode can be a low cost one such as IN4148 or BAT54. 5V BOOST DIODE Output Capacitor The output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the output voltage. The output capacitor is a basic component for the fast response of the power supply. In fact, during load transient, for the first few microseconds it supplies the current to the load. The converter recognizes the load transient and sets the duty cycle to maximum, but the current slope is limited by the inductor value. Maximum capacitance required can be calculated from the following equation: ΔIinductor 2 ) 2 Co = 2 −V 2 (Δ V + VOUT ) OUT L(IOUT + BST 1 AP5100 SW 6 10nF Figure 6. External Bootstrap Diode Under Voltage Lockout (UVLO) Under Voltage Lockout is implemented to prevent the IC from insufficient input voltages. The AP5100 has a UVLO comparator that monitors the internal regulator voltage. If the input voltage falls below the internal regulator voltage, the AP5100 will latch an under voltage fault. In this event the output will be pulled low and power has to be re-cycled to reset the UVLO fault. Equation 4 Where ΔV is the maximum output voltage overshoot. AP5100 Document number: DS32130 Rev. 2 - 2 7 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Applications Information (Continued) Internal Soft Start Soft start is traditionally implemented to prevent the excess inrush current. This in turn prevents the converter output voltage from overshooting when it reaches regulation. The AP5100 has an internal current source with a soft start capacitor to ramp the reference voltage from 0V to 0.810V. The soft start time is internally fixed at 200us (TYP). The soft start sequence is reset when there is a Thermal Shutdown, Under Voltage Lockout (UVLO) or when the part is disabled using the EN pin. Thermal Shutdown The AP5100 has on-chip thermal protection that prevents damage to the IC when the die temperature exceeds safe margins. It implements a thermal sensing to monitor the operating junction temperature of the IC. Once the die temperature rises to approximately 140°C, the thermal protection feature gets activated .The internal thermal sense circuitry turns the IC off thus preventing the power switch from damage. A hysteresis in the thermal sense circuit allows the device to cool down to approximately 120°C before the IC is enabled again. This thermal hysteresis feature prevents undesirable oscillations of the thermal protection circuit. Current Limit The AP5100 has cycle-by-cycle current limiting implementation. The voltage drop across the internal highside mosfet is sensed and compared with the internally set current limit threshold. This voltage drop is sensed at about 30ns after the HS turns on. When the peak inductor current exceeds the set current limit threshold, current limit protection is activated. During this time the feedback voltage (VFB) drops down. When the voltage at the FB pin reaches 0.4V, the internal oscillator shifts the frequency from the normal operating frequency of 1.4MHz to a foldback frequency of 480kHz. The current limit is reduced to 70% of nominal current limit when the part is operating at 480kHz. This low Fold-back frequency prevents runaway current. PC Board Layout This is a high switching frequency converter. Hence attention must be paid to the switching currents interference in the layout. Switching current from one power device to another can generate voltage transients across the impedances of the interconnecting bond wires and circuit traces. These interconnecting impedances should be minimized by using wide, short printed circuit traces. The input capacitor needs to be as close as possible to the IN and GND pins. The external feedback resistors should be placed next to the FB pin. AP5100 Document number: DS32130 Rev. 2 - 2 8 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency Ordering Information AP5100 W G - 7 Package W : SOT26 Device Package Code W Packaging (Note 6) SOT26 Green G : Green Packing 7 : Tape & Reel AP5100WG-7 Note: 13” Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7 6. 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. Marking Information SOT26 ( Top View ) 6 5 4 7 XX Y W X 1 2 3 XX : Identification Code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week X : A~Z : Green Identification Code AJ Part Number AP5100W Package SOT26 Package Outline Dimensions (All Dimensions in mm) SOT26 AP5100 Document number: DS32130 Rev. 2 - 2 9 of 10 www.diodes.com November 2010 © Diodes Incorporated AP5100 1.2A Step-Down Converter with 1.4MHz Switching Frequency 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. 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