Techcode® 3A 52KHz ÓÉ Foxit PDF Editor ±à¼°æȨËùÓÐ (c) by Foxit Software Company, 2004 ½öÓÃÓÚÆÀ¹À¡£ DATASHEET PWM Buck DC/DC Converter TD2576 汪工 ＴＥＬ：１３８２８７１９４１０ ＱＱ：１９２９７９４２３８ General Description Features The TD2576 is a series of easy to use fixed and adjustable step-down (buck) switch-mode voltage regulators. These devices are available in fixed output voltage of 3.3V, 5V, and an adjustable output version. Both versions are capable of driving a 3A load with excellent line and load regulation. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation, and a fixed-frequency oscillator. The output voltage is guaranteed to ±3% tolerance under specified input voltage and output load conditions. The oscillator frequency is guaranteed to ±15%. External shutdown is included, featuring typically 80 µA standby current. Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions. The TD2576 is available in TO-220B-5L TO220-5L and TO-263-5L packages. z z z z z z z z z z z z 3.3V, 5V and adjustable output versions Output adjustable from 1.23v to 43V Fixed 52KHz frequency internal oscillator Guaranteed 3A output load current Input voltage range up to 45V Low power standby mode, IQ typically 80 µA TTL shutdown capability Excellent line and load regulation Requires only 4 external components High efficiency Thermal shutdown and current limit protection Available in TO-220B/TO220 and TO-263 packages Applications z z z z z z z Simple High-efficiency step-down regulator On-card switching regulators Positive to negative converter LCD monitor and LCD TV DVD recorder and PDP TV Battery charger Step-down to 3.3V for microprocessors Package Types TO220B5L TO2205L TO2635L Figure 1. Package Types of TD2576 December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 1 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Pin Configurations Figure 2 Pin Configuration of TD2576 (Top View) Pin Description Pin Number Pin Name 1 Vin 2 Output 3 GND 4 FB 5 ON/OFF Description Input supply voltage Switching output Ground Output voltage feedback ON/OFF shutdown Active is “Low” or floating December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 2 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Ordering Information TD2576 □ □ Circuit Type Output Voltage: 33:3.3V 50:5V ADJ:ADJ Package T:TO220B-5L L:TO220-5L S:TO263-5L Function Block Figure 3 Function Block Diagram of TD2576 December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 3 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Absolute Maximum Ratings Note1: Stresses greater than those listed under Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability. Parameter Symbol Value Unit Input Voltage VIN -0.3 to 45 V Feedback Pin Voltage VFB -0.3 to Vin+0.3 V ON/OFF Pin Voltage VEN -0.3 to Vin+0.3 V Output Pin Voltage VSW -0.3 to Vin+0.3 V Power Dissipation PD Internally limited mW Operating Junction Temperature TJ 150 ºC Storage Temperature TSTG -65 to 150 ºC Lead Temperature (Soldering, 10 sec) TLEAD 260 ºC 2000 V ESD (HBM) MSL Level3 Thermal Resistance-Junction to Ambient Thermal Resistance-Junction to Case 23 3.5 RθJA RθJC ºC / W ºC / W Recommended Operating Conditions Parameter Symbol Min. Max. Unit Input Voltage VIN 3.6 45 V Operating Junction Temperature TJ -40 125 ºC Operating Ambient Temperature TA -40 85 ºC December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 4 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Electrical Characteristics Specifications with boldface type are for full operationg temperature range, the other type are for TJ=25OC. Note1: Thermal resistance with copper area of approximately 3 in2. Parameters Symbol Test Condition Min. Typ. Max. Unit Feedback bias current Ib Adjustable only, VFB=1.3V 10 50/100 nA Quiescent current IQ VFB=12V force driver off 5 10 mA Standby quiescent current ISTBY ON/OFF=5V, VIN=36V 80 200/250 uA Oscillator frequency FOSC 52 58 KHz Saturation voltage VSAT IOUT=3A 1.2 1.4/1.5 V Current Limit ICL Peak Current (VFB=0V) 4.5 5.5/6.5 A Output leakage current IL IL Output=0V (VFB=12V) 50 uA 2 30 mA 1.3 0.6 V Output leakage current 47 Output=-1V (VIN=36V) ON/OFF pin logic input Threshold voltage VIL VIH IH IL ON/OFF pin input current Low (Regulator ON) High (Regulator OFF) VLOGIC=2.5V(Regulator 2.0 1.3 V 5 15 uA VLOGIC=0.5V(Regulator ON) 0.02 5 uA OFF) Thermal Resistance Junction to Case θJC TO220B-5L/TO220-5L TO263-5L 2.5 3.5 Thermal Resistance Junction to Ambient (Note1) θJA TO220B-5L/TO220-5L TO263-5L 28 23 O C/W O C/W December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 5 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Electrical Characteristics(Cont.) Specifications with boldface type are for full operationg temperature range, the other type are for TJ=25OC. Note1: Thermal resistance with copper area of approximately 3 in2. Parameters Symbol Vout: Output Voltage TD2576 ADJ η: Efficiency Vout: Output Voltage TD2576 Test Condition 11V ≤ VIN ≤ 45V, 0.2A ≤ ILOAD≤3A, VOUT for 9V Min. 1.193/ 1.180 VIN=12V,VOUT=9V,ILOAD =3A 4.75V≤VIN≤45V, 0.2A≤ ILOAD≤3A Typ. 1.23 Max. 1.267/ 1.280 88 3.168/ 3.135 3.3 Unit V % 3.432/ 3.465 V 3.3V η: Efficiency Vout: Output Voltage TD2576 VIN=12V, ILOAD=3A 7V ≤ VIN ≤ 45V, 0.2A ≤ ILOAD≤3A 76 4.800/ 4.750 5.0 % 5.200/ 5.250 V 5V η: Efficiency VIN=12V, ILOAD=3A 83 % December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 6 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Typical Performance Characteristics Figure 4. Output Voltage vs. Temperature Figure 5. Switching Frequency vs. Temperature Figure 6. Output Saturation Characteristics Figure 7. Quiescent Current vs. Temperature December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 7 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Typical Performance Characteristics(Cont.) Figure 8. ON/OFF Pin Voltage Figure 9. ON/OFF Pin Sink Current Figure 10. Output Saturation Characteristics December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 8 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Typical Application Circuit Figure 11. Typical Application of TD2576 For 3.3V Input Voltage Inductor (L1) 6V ~ 18V 6V ~ 45V 47uh 68uh Output Capacitor (Cout) Through Hole Electrolytic Surface Mount Tantalum 470uf/25V 330uf/6.3V 560uf/25V 330uf/6.3V Table 1. TD2576 Series Buck Regulator Design Procedure For 3.3V Figure 12. Typical Application of TD2576 For 5V Input Voltage Inductor (L1) 8V ~ 18V 8V ~ 45V 33uh 47uh Output Capacitor (Cout) Through Hole Electrolytic Surface Mount Tantalum 330uf/25V 220uf/10V 470uf/25V 330uf/10V Table 2. TD2576 Series Buck Regulator Design Procedure For 5V December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 9 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Figure 13. Typical Application of TD2576 For ADJ Note:In PCB layout. Reserved an area for CFF Vout 3.3V 5V 9V 12V R2 2.7K 11K 43K 13K R1 1.6K 3.6K 6.8K 1.5K Cf (Operational) 33nf 10nf 1.5nf 1nf Table 3. Vout VS. R1, R2, Cf Select Table Output Voltage 3.3V 5V 9V 12V Input Voltage 6V ~ 18V 6V ~45V 8V ~ 18V 8V ~45V 12V ~18V 12V ~45V 15V ~ 18V 15V ~45V Inductor (L1) 47uh 68uh 33uh 47uh 47uh 47uh 47uh 47uh Output Capacitor (Cout) Through Hole Electrolytic 470uf/25V 560uf/25V 330uf/25V 470uf/25V 330uf/25V 470uf/25V 220uf/25V 330uf/25V Table 4. Typical Application Buck Regulator Design Procedure December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 10 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Function Description Pin Functions +VIN This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator Ground Circuit ground. Output Internal switch. The voltage at this pin switches between (+VIN – VSAT) and approximately – 0.5V, with a duty cycle of approximately VOUT / VIN. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept a minimum. Feedback Senses the regulated output voltage to complete the feedback loop. ON/OFF Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 80uA. Pulling this pin below a threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin above 1.3V (up to a maximum of 25V) shuts the regulator down. If this shutdown feature is not needed, the ON /OFF pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the ON condition. Thermal Considerations The TD2576 is available in two packages, a 5-pin TO-220B/TO-220 and a 5-pin surface mount TO-263. The TO-220B/TO-220 package needs a heat sink under most conditions. The size of the heatsink depends on the input voltage, the output voltage, the load current and the ambient temperature. The TD2576 junction temperature rises above ambient temperature for a 3A load and different input and output voltages. The data for these curves was taken with the TD2576 (TO-220B/TO-220 package) operating as a buck switching regulator in an ambient temperature of 25oC (still air). These temperature rise numbers are all approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require more heat sinking. The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. The copper and the board are the heat sink for this package and the other heat producing components, such as the catch diode and inductor. The PC board copper area that the package is soldered to should be at least 0.4 in2, and ideally should have 2 or more square inches of 2 oz. Additional copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in2, only small improvements in heat dissipation are realized. If further thermal improvements are needed, double sided, multilayer PC board with large copper areas and/or airflow are recommended. The TD2576 (TO-263 package) junction temperature rise above ambient temperature with a 3A load for various input and output voltages. This data was taken with the circuit operating as a buck switching regulator with all components mounted on a PC board to simulate the junction temperature under actual operating conditions. This curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware that there are many factors that can affect the junction temperature. When load currents higher than 3A are used, double sided or multilayer PC boards with large copper areas and/or airflow might be needed, especially for high ambient temperatures and high output voltages. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (Once exception to December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 11 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Function Description(Cont.) this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further. Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to FB(TD2576-ADJ) The voltage divider divides the output voltage down by the ratio: VFB = VOUT * R1 / (R1 + R2) Thus the output voltage is: VOUT = 1.235 * (R1 + R2) / R1 R1 can be as high as 100KΩ, but a typical value is 10KΩ. Using that value, R2 is determined by: R2 ~= 8.18 * (VOUT – 1.235) (KΩ) For example, for a 3.3V output voltage, R1 is 10KΩ, and R2is 17KΩ. Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor results in less ripple current that in turn results in lower output ripple voltage. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. Choose an inductor that does not saturate under the worst-case load conditions. A good rule for determining the inductance is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum load current. Also, make sure that the peak inductor current (the load current plus half the peak to peak inductor ripple current) is below the TBDA minimum current limit. The inductance value can be calculated by the equation: L = (VOUT) * (VIN-VOUT) / VIN * f * ∆I Where VOUT is the output voltage, VIN is the input voltage, f is the switching frequency, and ∆I is the peak-to-peak inductor ripple current. Input Capacitor The input current to the step-down converter is discontinuous, and so a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. The input capacitor value should be greater than 10μF. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating. Its RMS current rating should be greater than approximately 1/2 of the DC load current. For insuring stable operation should be placed as close to the IC as possible. Alternately a smaller high quality ceramic 0.1μF capacitor may be placed closer to the IC and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. All ceramic capacitors should be places close to the TD2576. Output Capacitor The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple low. The characteristics of the output capacitor also affect the stability of the regulation control system. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 12 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Function Description(Cont.) and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: VRIPPLE ~= 1.4 * VIN * (fLC/fSW)^2 Where VRIPPLE is the output ripple voltage, VIN is the input voltage, fLC is the resonant frequency of the LC filter, fSW is the switching frequency. In the case of tanatalum or lowESR electrolytic capacitors, the ESR dominates the impedance at the switching frequency, and so the output ripple is calculated as: VRIPPLE ~= ∆I * RESR Where VRIPPLE is the output voltage ripple, ∆I is the inductor ripple current, and RESR is the equivalent series resistance of the output capacitors. Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the high-side switch is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Table 1 provides the Schottky rectifier part numbers based on the maximum input voltage and current rating. Choose a rectifier who’s maximum reverse voltage rating is greater than the maximum input voltage, and who’s current rating is greater than the maximum load current. Feedforward Capacitor (CFF) For output voltages greater than approximately 8V, an additional capacitor is required. The compensation capacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, R2. It provides additional stability for high output voltages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors. This capacitor type can be ceramic, plastic, silver mica, etc.(Because of the unstable characteristics of ceramic capacitors made with Z5U material, they are not recommended.) Note:In PCB layout. Reserved an area for CFF. Over Current Protection (OCP) The cycle by cycle current limit threshold is set between 4A and 5A. When the load current reaches the current limit threshold, the cycle by cycle current limit circuit turns off the high side switch immediately to terminate the current duty cycle. The inductor current stops rising. The cycle by cycle current limit protection directly limits inductor peak current. The average inductor current is also limited due to the limitation on peak inductor current. When the cycle by cycle current limit circuit is triggered, the output voltage drops as the duty cycle is decreasing. Thermal Management and Layout Consideration In the TD2576 buck regulator circuit, high pulsing current flows through two circuit loops. The first loop starts from the input capacitors, to the VIN pin, to the VOUT pins, to the filter inductor, to the output capacitor and load, and then returns to the input capacitor through ground. Current flows in the first loop when the high side switch is on. The second loop starts from the inductor, to the output capacitors and load, to the GND pin of the TD2576, and to the VOUT pins of the TD2576. Current flows in the second loop when the low side diode is on. In PCB layout, minimizing the two loops area reduces the December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 13 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Function Description(Cont.) noise of this circuit and improves efficiency. A ground plane is recommended to connect input capacitor, output capacitor, and GND pin of the TD2576. In the TD2576 buck regulator circuit, the two major power dissipating components are the TD2576 and output inductor. The total power dissipation of converter circuit can be measured by input power minus output power. Ptotal _loss = V IN × IIN – V O × IO The power dissipation of inductor can be approximately calculated by output current and DCR of inductor. Pinductor _loss= IO 2 × Rinductor × 1.1 The junction to ambient temperature can be got from power dissipation in the TD2576 and thermal impedance from junction to ambient. Several layout tips are listed below for the best electric and thermal performance. 1. Do not use thermal relief connection to the VIN and the GND pin. Pour a maximized copper area to the GND pin and the VIN pin to help thermal dissipation. 2. Input capacitor should be connected to the VIN pin and the GND pin as close as possible. 3. Make the current trace from VOUT pins to L to the GND as short as possible. 4. Pour copper plane on all unused board area and connect it to stable DC nodes, like VIN, GND, or VOUT. 5. Keep sensitive signal traces such as trace connecting FB pin away from the VOUT pins. T (jun-amb) =(Ptotalloss–Pinductorloss)× ΘJA The maximum junction temperature of TD2576 is 145°C, which limits the maximum load current capability. Please see the thermal de-rating curves for the maximum load current of the TD2576 under different ambient temperatures. The thermal performance of the TD2576 is trongly affected by the PCB layout. Extra care should be taken by users during the design process to nsure that the IC will operate under the recommended environmental conditions. December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 14 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Package Information TO220B5L December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 15 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Package Information(Cont.) TO2205L December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 16 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Package Information(Cont.) TO2635L December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 17 Techcode® DATASHEET 3A 52KHz TD2576 PWM Buck DC/DC Converter Design Notes December, 20, 2005. Techcode Semiconductor Limited www.tongchuangwei.com 18