BM2576 3A DC/DC GENERAL DESCRIPTION FEATURES The BM2576 series are step-down switching regulators with Guaranteed 3A output current all required active functions. It is capable of driving 3A load 3.3V, 5V, and adjustable versions with excellent line and load regulations. These devices are Wide input voltage range, up to 40V available in fixed output voltages of 3.3V, 5V, and an Internal oscillator of 52KHz fixed frequency adjustable output version. Wide adjustable version output voltage range, from 1.23V to 37V±4% max over line and load conditions The BM2576 series offers a high-efficiency replacement for Low standby current, typ. 70µA, at shutdown mode popular three-terminal linear regulators. Also it requires a Requires only 4 external components minimum number of external components. It substantially not Thermal shutdown and current limit protection only reduces the area of board size but also the size of the P+ product enhancement tested heat sink, and in some cases no heat sink is required. ±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. APPLICATIONS LCD Monitors ADD-ON Cards Switching Regulators High Efficiency Step-Down Regulators Car Electronic ORDERING INFORMATION Package Type TO-220 TO-263 Temperature Range Output Voltage BM2576SCN220 BM2576SCN263 -40℃ ~ +125℃ 3.3V BM2576ZJCN220 BM2576ZJCN263 -40℃ ~ +125℃ 5.0V BM2576CN220 BM2576CN263 -40℃ ~ +125℃ ADJ. 2003/08/07 www.bookly.com Page 1 BM2576 3A DC/DC PIN CONFIGURATION TO-263 Top View TO-220 Top View ENABLE GND 5 4 3 V OUT V IN 2 1 FB ENABLE 1 2 GND V OUT V IN FB 3 4 5 ABSOLUTE MAXIMUM RATINGS Input Voltage (VPOWER) …….………………………………………….……. +45V ENABLE Pin Input Voltage ….…………………………………. –0.3V ≦V≦VIN Operating Junction Temperature Range, TJ ……………...… 0℃ to +150℃ Storage Temperature ………………………………….….…... -65℃ to +150℃ Lead Temperature (10 sec.) ……..……………………..….…………….... 260℃ POWER DISSIPATION TABLE Package ΘJA (℃/W) TO-220 TO-263 45 45 Derating factor (mW/℃) TA >= 25℃ 22.2 22.2 TA <= 25℃ Power rating (mW) 2775 2775 TA = 70℃ TA = 85℃ Power rating (mW) Power rating (mW) 1776 1443 1776 1443 Note: 1. ΘJA : Thermal Resistance-Junction to Ambient, DF: Derating factor, PO: Power consumption. 2. Junction Temperature Calculation: TJ = TA + (PD x ΘJA ), PO = DF x (TJ – TA) The ΘJA numbers are guidelines for the thermal performance of the device/PC-board system. All of the above assume no ambient airflow. ΘJT : Thermal Resistance-Junction to Ambient, TC: case (Tab) temperature, TJ = TC + (PD x ΘJA ) RESOMMENDED OPERATING CONDITIONS Parameter Input Voltage (VIN) Temperature Range 2003/08/07 Symbol VIN TJ www.bookly.com Min. -40 Typ. Max 40 125 Units V ℃ Page 2 BM2576 3A DC/DC ELECTRICAL CHARACTERISTICS Electrical Characteristics at IOUT = 0mA, and TJ = +25℃; unless otherwise noted Parameter Device Output Voltage BM2576S (Note 1) BM2576ZJ Test circuit of Figure 1 Output Voltage BM2576S 6V<=VIN <=40V (Note 1) BM2576ZJ 8V<=VIN <=40V BM2576S 6V<=VIN <=40V BM2576ZJ 8V<=VIN <=40V BM2576 (Adj) Test circuit of Figure 2 Output Voltage (Note 1) Feedback Voltage (Note 1) Feedback Voltage (Note 1) Feedback Voltage (Note 1) BM2576 (Adj) BM2576 (Adj) V V 3.135 3.300 3.482 V 4.750 5.000 5.250 V VOUT =5V 1.217 1.230 1.243 V 0.5A<=ILOAD <=3A 1.193 1.230 1.267 V 1.180 1.230 1.286 V -40℃<=TJ<=125℃ Test circuit of Figure 1 0.5A<=ILOAD <=3A, -40℃<=TJ<=125℃ 75 ILOAD =3A Note 2 47 52 58 -40℃<=TJ<=125℃ 42 52 63 5 10 mA 70 200 µA 1.4 1.8 -40℃<=TJ<=125℃ VOUT =5V TJ=25℃ -40℃<=TJ<=125℃ Note 5 Current Limit Note 2,4 Output Leakage Current Note 3 VIH (VOUT =0V) % TJ=25℃ (Adj. Version only) Duty Cycle (ON) 77 TJ=25℃ ILOAD =3A (Note 4) % 77 ILOAD =3A, VOUT =5V ENABLE = 5V 2003/08/07 V 5.100 V Standby Current ENABLE Input Current 3.366 5.000 3.432 Note 3 ENABLE Threshold Voltage 3.300 4.900 5.200 Quiescent Current Feedback Bias Current 3.234 3.300 Test circuit of Figure 2 BM2576(adj) Saturation Voltage Max. 5.000 8V<=VIN <=40V, VOUT =5V BM2576ZJ Oscillator Frequency Typ. 3.168 0.5A<=ILOAD <=3A, Test circuit of Figure 2 Unit Min. 4.800 0.5A<=ILOAD <=3A 8V<=VIN <=40V, VOUT =5V BM2576S Efficiency BM2576 Test Conditions 2.0 50 100 500 93 98 TJ=25℃ 4.2 7 8.8 3.5 7.2 9.0 VOUT =0V 0.3 2 VOUT =-1V 9 20 2.2 -40℃<=TJ<=125℃ 2.4 VIL (VOUT = Normal Output TJ=25℃ Voltage) -40℃<=TJ<=125℃ IIH ( ENABLE = 5V) IIH ( ENABLE = 0V) www.bookly.com 1.4 1.2 V nA % -40℃<=TJ<=125℃ TJ=25℃ kHz A mA V 1.0 0.8 12 30 0 10 Page 3 V µA BM2576 3A DC/DC 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 connect to VOUT. Note 5: FB is removed from VOUT and connected to 0V. BLOCK DIAGRAM 2003/08/07 www.bookly.com Page 4 BM2576 3A DC/DC APPLICATION CIRCUIT BM2576 BM2576 2003/08/07 www.bookly.com Page 5 BM2576 3A DC/DC TYPICAL CHARACTERISTICS 2003/08/07 www.bookly.com Page 6 BM2576 3A DC/DC 2003/08/07 www.bookly.com Page 7 BM2576 3A DC/DC APPLICATION INFORMATION It is required that VIN must be bypassed with at least a 100uF electrolytic capacitor for stability. Also, it is strongly recommended the capacitor’s leads must be dept short, and located near the regulator as possible. For low operating temperature range, for example, below -25℃, 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 age. Paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. Output Capacitors (COUT) An output capacitor is also required to filter the output voltage and is needed for loop stability. The capacitor should be located near the BM2576 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 (220uF – 1000uF) 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 provide a return path for the inductor current when the switch is off. It should be located close to the BM2576 using short leads and short printed circuit traces as possible. To satisfy the need of 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). Besides, 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. 2003/08/07 www.bookly.com Page 8 BM2576 3A DC/DC Output Voltage Ripple and Transients 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 voltages at the switcher frequency, typically about 1% of the output voltages, and may also contain short voltage spikes 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 (30uH & 100uF) (as shown in Figure 3) will possibly provide a 10X reduction in output ripple voltage and transients. Inductor Selection The BM2576 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 forced 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. Inductors are available in different styles such as pot core, toriod, 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 voltages in the scope probe. 2003/08/07 www.bookly.com Page 9 BM2576 3A DC/DC 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. 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 BM2576 as possible in order to minimize the noise introduction. ENABLE 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. 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 either connection may be used. Heatsink and Thermal Consideration Although the BM2576 requires only a small heatsink for most cases, the following thermal consideration is important for all operation. With the package thermal resistances θJA and θJC, total power dissipation can be estimated as follows: PD = (VIN x IQ) + (VOUT / VIN)(ILOAD x VSAT); When no heatsink is used, the junction temperature rise can be determined by the following: ∆TJ = PD x θJA; With the ambient temerpature, the actual junction temperature will be: TJ = ∆TJ + TA; If the actual operating junction temperature is out of the safe operating junction temperature (typically 125℃), then a heatsink is required. When using a heatsink, the junction temperature rise will be reduced by the following: ∆TJ = PD x (θJC + θinterface + θHeatsink); 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. 2003/08/07 www.bookly.com Page 10 BM2576 3A DC/DC PACKAGE DIMENSION TO-220 (N220) C B S T F A B C A D F G J K 1 2 3 4 5 N R S K T G N R J D TO-263 (N263) C D L K B I A G 2003/08/07 F E www.bookly.com Page 11