TS2576 3A Step Down Switching Voltage Regulator Pin assignment: 1. Input 2. Output 3. Ground 4. Feedback 5. Enable 52KHz Oscillating Frequency Output Current up to 3A Enable Input Control General Description The TS2576 Series are step-down switching regulators with all required active functions. It is capable of driving 3A load with excellent line and load regulations. These devices are available in fixed output voltages of 3.3V, 5V, and an adjustable output version. The TS2576 series offers a high-efficiency replacement for popular three-terminal linear regulators. Also it requires a minimum number of external components. It substantially not only reduces the area of board size but also the size of heat sink, and in some cases no heat sink is required. The ±4% tolerance on output voltage within specified input voltages and output load conditions is guaranteed. Also, the oscillator frequency accuracy is within ±10%. External shutdown is included. Featuring 70µA (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. This series are offered in 5-pin TO-263, TO-220 package. Features Ordering Information Guaranteed 3A output current 3.3V, 5V, and adjustable versions Wide input voltage range, up to 40V Internal oscillator of 52KHz fixed frequency Part No. Operating Temp. (Ambient) TO-220-5L TS2576CZ5-xx o -20 ~ +85 C TS2576CZ5 Wide adjust version output voltage range, from 1.23V Package to 37V ±4% max. at over line and load conditions. TS2576CM5-xx Low standby current, typ. 70µA, at shutdown mode TS2576CM5 Requires only 4 external components Thermal shutdown and current limit protection P+ product enhancement tested TO-263-5L Note: Where xx denotes voltage option, available are 12V, 5V and 3.3V. Leave blank for adjustable version. Contact factory for additional voltage options. Applications LCD Monitors Efficient Pre-regulator for Linear Regulators ADD-ON Cards Switching Regulators Positive to Negative converter (Buck-Boost) High Efficiency Step-Down Regulators Absolute Maximum Rating Input Voltage ENABLE Pin Input Voltage Vin +45 V Vin (operate) -0.3V ≤ V ≤ Vin V PD Internal Limited Power Dissipation Operating Junction Temperature Range TJ Storage Temperature Range TSTG W -0 ~ +150 o C -65 ~ +150 o C o Lead Soldering Temperature (260 C) TO-220-5L / TO-263-5L Package TS2576 5 1-7 S 2003/12 rev. A Block Diagram Electrical Characteristics o Vin = 12V, IL = 500mA, Ta = 25 C unless otherwise specified. Parameter Conditions Min Typ Max 3.3 1.02|Vo| Unit TS2576-3.3V Output Voltage (Note 1) Vin=12V, IL=0.5A (Figure 1) 0.98|Vo| Output Voltage (Note 1) 0.5A ≤ IL ≤ 3A, 6V ≤ Vin ≤ 40V 0.96|Vo| 1.04|Vo| V % (Figure 1) Efficiency Vin=12V, IL=3A -- 75 -- 5.0 1.02|Vo| TS2576-5V Output Voltage (Note 1) Vin=12V, IL=0.5A(Figure 1) 0.98|Vo| Output Voltage (Note 1) 0.5A ≤ IL ≤ 3A, 8V ≤ Vin ≤ 40V 0.96|Vo| 1.04|Vo| V % (Figure 1) Efficiency Vin=12V, IL=3A -- 77 -- 12 1.02|Vo| TS2576-12V Output Voltage (Note 1) Vin=25V, IL=0.5A (Figure 1) 0.98|Vo| Output Voltage(Note 1) 0.5A ≤ IL ≤ 3A, 15V ≤ Vin ≤ 40V 0.96|Vo| 1.04|Vo| V % (Figure 1) Efficiency Vin=15V, IL=3A -- 88 -- 1.23 1.02|Vo| TS2576 Feedback Voltage (Note 1) Vin=12V, Vout=5V,IL=0.5A (Figure 2) 0.98|Vo| Feedback Voltage (Note 1) 0.5A ≤ IL ≤ 3A, 8V ≤ Vin ≤ 40V, 0.96|Vo| 1.04|Vo| V -- % Vout=5V (Figure 2) Efficiency TS2576 Vin=12V, Vout=5V, IL=3A 2-7 -- 77 2003/12 rev. A All Output Voltage Version (Vin=12V for 5V, 3.3V and Adjustable version, Vin=25V for 12V version, IL = 500mA) Oscillator Frequency (Note 2) 47 52 58 kHz -- 5 10 mA Standby Current ENABLE =5V -- 70 200 uA Saturation Voltage (Note 4) ILOAD=3A -- 1.4 1.8 V Feedback Bias Current VOUT=5V (Adj. Version only) -- 50 100 nA Duty Cycle (Note 5) Operating (ON) 93 98 -- % A Quiescent Current (Note 3) Current Limit (Note 2)(Note 4) Output Leakage Current (Note 3) ENABLE Threshold Voltage ENABLE Input Current 4.2 7.0 8.8 VOUT=0V -- 0.3 2 VOUT=-1V -- 7.5 30 2.2 1.4 -- VIL(VOUT=Normal Output Voltage) -- 1.2 1.0 IIH (ENABLE =5V) -- 12 30 IIH (ENABLE =0V) -- 0 10 VIH (VOUT=0V) mA V uA Note 1: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. Refer to Application information for details. Note 2: The oscillator frequency reduces to approximately 11KHz in the event of fault conditions, such as output short or overload. And the regulated output voltage will drop approximately 40% from the nominal output voltage. This self-protection feature lowers the average power dissipation by lowering the minimum duty cycle from 5% down to approximately 2%. Note 3: For these parameters, FB is removed from VOUT and connected to +12V to force the output transistor OFF. Note 4: VOUT pin sourcing current. No diode, inductor or capacitor connected to VOUT. Note 5: FB is removed from VOUT and connected to 0V. TS2576 3-7 2003/12 rev. A Typical Application Circuit Figure 1 Fixed Voltage Version Figure 2: Adjustable Voltage Version Figure 3: LC filter for Low Output Ripple TS2576 4-7 2003/12 rev. A Application Information Inductor Selection It is required that VIN must be bypassed with at least a 100µF electrolytic capacitor for stability. Also, it is strongly recommended the capacitor’s leads must be dept short, and located near the regulator as possible. The TS2576 can be used for either continuous or discontinuous modes of operation. Each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. With relatively heavy load currents, the circuit operates in the continuous mode (inductor current always flowing). But under light Load conditions, the circuit will be force to the discontinuous mode (inductor current falls to zero for a period of time). For light loads (less than approximately 300mA) it may be desirable to operate the regulator in the discontinuous mode, primarily because of the lower inductor values required for the discontinuous mode. Indictors are available in different styles such as pot core, toroid, E-frame, bobbin core, et., as well as different core materials such as ferrites and powdered iron. The least expensive, the bobbin core type, consists of wire wrapped on a ferrite rod core. This type of construction makes for an inexpensive inductor, but since the magnetic flux is not completely contained within the core, it generates more electromagnetic interference (EMI). This EMI can cause problems in sensitive circuits, or can give incorrect scope readings because of induced voltage in the scope probe. An inductor should not be operated beyond its maximum rated current because it may saturate. When an inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding). This will cause the switch current to rise very rapidly. Different inductor types have different saturation characteristics, and this should be well considered when selecting as inductor. For low operating temperature range, for example, below o -25 C, the input capacitor value may need to be larger. This is due to the reason that the capacitance value of electrolytic capacitors decreases and the ESR increases with lower temperatures and ago. Paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. Output Capacitor An output capacitor is also required to filter the output voltage and is needed for loop stability. The capacitor should be located near the TS2576 using short PC board traces. Low ESR types capacitors are recommended for low output ripple voltage and good stability. Generally, low value or low voltage (less than 12V) electrolytic capacitors usually have higher ESR numbers, For example, the lower capacitor values (220µF - 1000µF) will yield typically 50mV to 150mV of output ripple voltage, while larger-value capacitors will reduce the ripple to approximately 20mV to 50mV. The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of the output capacitor and the amplitude of the inductor ripple current ( IIND) Output Ripple Voltage = ( IIND) x (ESR of COUT) Some capacitors called “high-frequency”, “low-inductance”, or “low-ESR” are recommended to use to further reduce the output ripple voltage to 10mV or 20mV. However, very low ESR capacitors, such as tantalum capacitors, should be carefully evaluated. Catch Diode This diode is required to return path for the inductor current when the switch is off. It should be located close to the TS2576 using short leads and short printed circuit traces as possible. To satisfy the need to fast switching speed and low forward voltage drop, Schottky diodes are widely used to provide the best efficiency, especially in low output voltage switching regulators (less than 5V). Beside, Fast-Recovery, high-efficiency, or ultra fast recovery diodes are also suitable. But some types with an abrupt turn-off characteristic may cause instability and EMI problems. A fast recovery diode with soft recovery characteristics is better choice. TS2576 5-7 Feedback Connection For fixed output voltage version, the FB (feedback) pin must be connected to VOUT. For the adjustable version, it is important to place the output voltage ratio resistors near TS2576 as possible in order to minimize the noise introduction. Enable Input It is required that the ENABLE must not be left open. For normal operation, connect this pin to a ”LOW” voltage (typically, below 1.6V). On the other hand, for standby mode, connect this pin with a “HIGH” voltage. This pin can be safely pulled up to +VIN without a resistor in series with it. 2003/12 rev. A Grounding To maintain output voltage stability, the power ground connections must be low-impedance. For the 5-lead TO-220 and TO-263 style package, both the tab and pin 3 are ground and rather connection may be used. Thermal Characteristics The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output capacitor. The output ripple voltage of a switching power supply will contain a sawtooth ripple voltage at the switcher frequency, typically about 1% of the output voltages, and may also contain short voltage spokes of the sawtooth waveform. Due to the fast switching action, and the parasitic inductance of the output filter capacitor, there is voltage spikes presenting at the peaks of the sawtooth waveform. Cautions must be taken for stray capacitance. Wiring inductance, and even the scope probes used for transients evaluation. To minimize these voltage spikes, shortening the lead length and PCB traces is always the first thought. Further more, an additional small LC filter (30µH & 100µF) (as shown in Figure 3) will possibly provide a 10X reduction in output ripple voltage and transients. Heatsink and Thermal Consideration Although the TS2576 requires only a small heatsink for most cases, the following thermal consideration is important for all operation. With the package thermal resistances Өja and Өjc , total power dissipation can be estimated as follows: PD= (Vin x Iq) + (Vout / Vin) (Iout x Vsat); When no heatsink is used, the junction temperature rise can be determined by the following: ∆TJ = PD x Өja With the ambient temperature, the actual junction temperature will be: Tj = ∆Tj + Ta If the actual operating junction temperature is out of the safe operating junction temperature (typically 125oC), then a heatsink is required. When using a heatsink, the junction temperature rise will be reduced by the following : ∆Tj= PD x (Өjc + Ө interface + Ө heatsink ); Also one can see from the above, it is important to choose an heatsink with adequate size and thermal resistance, such that to maintain the regulator’s junction temperature below the maximum operating temperature. TS2576 6-7 2003/12 rev. A TO-220-5L Mechanical Drawing G B A TO-220 DIMENSION H C DIM M N L I F K E MILLIMETERS INCHES A MIN 10.00 MAX 10.50 MIN 0.394 MAX 0.413 B 3.240 4.440 0.128 0.175 C D 2.440 0.260 2.940 1.020 0.096 0.010 0.116 0.040 E 1.570 1.830 0.062 0.072 F G 13.31 4.475 14.13 5.225 0.524 0.176 0.556 0.206 H 1.170 1.370 0.046 0.054 I J 27.60 2.175 29.44 2.925 1.087 0.086 1.159 0.115 K 0.297 0.477 0.012 0.019 L 8.280 8.800 0.326 0.346 M N 6.010 14.29 6.510 15.31 0.237 0.563 0.256 0.603 J D TO-263-5L Mechanical Drawing TO-263 DIMENSION A E F J B I C G D TS2576 H 7-7 DIM MILLIMETERS MIN MAX INCHES MIN MAX A 10.220 10.260 0.402 0.404 B C 14.600 0.750 15.870 0.770 0.575 0.030 0.625 0.030 D 1.573 1.827 0.062 0.072 E F 4.560 1.240 4.570 1.270 0.179 0.049 0.180 0.050 G 2.280 2.790 0.090 0.110 H I 0.280 8.240 0.320 8.280 0.011 0.324 0.013 0.326 J 1.540 1.800 0.060 0.071 2003/12 rev. A