LM2575S-ADJ/TR

LM2575 1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR FEATURES • • • • • • • • • Fixed 3.3-V, 5-V, 12-V, and 15-V Options With ±5% Regulation (Max) Over Line, Load, and Temperature Conditions Adjustable Option With a Range of 1.23 V to 37 V and ±4% Regulation (Max) Over Line, Load, and Temperature Conditions Specified 1-A Output Current Wide Input Voltage Range…4.75 V to 40 V Requires Only Four External Components (Fixed Versions) and Uses Readily Available Standard Inductors 52-kHz (Typ) Fixed-Frequency Internal Oscillator TTL Shutdown Capability With 50-µA (Typ) Standby Current High Efficiency…as High as 88% (Typ) Thermal Shutdown and Current-Limit Protection With Cycle-by-Cycle Current Limiting APPLICATIONS • • • • Simple High-Efficiency Step-Down (Buck) Regulator Pre-Regulator for Linear Regulators On-Card Switching Regulators Positive-to-Negative Converter (Buck-Boost) DESCRIPTION/ORDERING INFORMATION The LM2575 greatly simplifies the design of switching power supplies by conveniently providing all the active functions needed for a step-down (buck) switching regulator in an integrated circuit. Accepting a wide input voltage range and available in fixed output voltages of 3.3 V, 5 V, 12 V, 15 V, or an adjustable output version, the LM2575 has an integrated switch capable of delivering 1 A of load current, with excellent line and load regulation. The device also offers internal frequency compensation, a fixed-frequency oscillator, cycle-by-cycle current limiting, and thermal shutdown. In addition, a manual shutdown is available via an external ON/OFF pin. The LM2575 represents a superior alternative to popular three-terminal linear regulators. Due to its high efficiency, it significantly reduces the size of the heat sink and, in many cases, no heat sink is required. Optimized for use with standard series of inductors available from several different manufacturers, the LM2575 greatly simplifies the design of switch-mode power supplies by requiring a minimal addition of only four to six external components for operation. The LM2575 is characterized for operation over the virtual junction temperature range of 0 °C to 85 °C. http://www.hgsemi.com.cn 1 2018 AUG LM2575 FUNCTIONAL BLOCK DIAGRAM VIN Unregulated DC Input Internal Regulator 1 + ON/OFF On/Off 5 CIN FEEDBACK 4 R2 R1 1 k
Fixed-Gain Error Amp + _ Comparator + _ Driver 1-A Switch OUTPUT L1 2 + D1 1.23-V Band-Gap Reference VOUT COUT GND 52-kHz Oscillator Reset Thermal Shutdown Current Limit 3 L O A D 3.3 V: R2 = 1.7 k
5 V: R2 = 3.1 k
12 V: R2 = 8.84 k
15 V: R2 = 11.3 k
ADJ: R1 = Open, R2 = 0 Ω A. Pin numbers are for the KTT (TO-263) package. FEEDBACK 4 7-V to 40-V Unregulated DC Input +VIN LM2575-05 1 3 + GND 5 OUTPUT 2 L1 L2 330 µH 20 µH 5-V Regulated Output 1-A Load ON/OFF CIN 100 µF D1 1N5819 + COUT 330 µF C1 100 µF + Optional Output Ripple Filter A. Pin numbers are for the KTT (TO-263) package. Figure 1. Typical Application Circuit (Fixed Version) http://www.hgsemi.com.cn 2 2018 AUG LM2575 Absolute Maximum Ratings (1) over operating free-air temperature range (unless otherwise noted) VIN MIN MAX 42 V –0.3 VIN V –1 V Supply voltage ON/OFF pin input voltage Output voltage to GND (steady state) TJ Maximum junction temperature Tstg Storage temperature range (1) –65 UNIT 150 °C 150 °C Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. Package Thermal Data (1) (1) PACKAGE BOARD θJC PDIP (N) High K, JESD 51-7 51°C/W TO-263 (KTT) High K, JESD 51-5 θJCB θJA 67°C/W TBD TBD Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambient temperature is PD = (TJ(max) – TA)/θJA. Operating at the absolute maximum TJ of 150°C can affect reliability. Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) VIN Supply voltage TJ Operating virtual junction temperature http://www.hgsemi.com.cn 3 MIN MAX 4.75 40 UNIT V 0 85 °C 2018 AUG LM2575 Electrical Characteristics ILOAD = 200 mA, VIN = 12 V for 3.3-V, 5-V, and adjustable versions, VIN = 25 V for 12-V version, VIN = 30 V for 15-V version (unless otherwise noted) (see Figure 2) PARAMETER TEST CONDITIONS VIN = 12 V, ILOAD = 0.2 A LM2575-33 4.75 V ≤ VIN ≤ 40 V, 0.2 A ≤ ILOAD ≤ 1 A VIN = 12 V, ILOAD = 0.2 A LM2575-05 VOUT Output voltage LM2575-12 LM2575-15 Feedback voltage η Efficiency LM2575-ADJ 8 V ≤ VIN ≤ 40 V, 0.2 A ≤ ILOAD ≤ 1 A MAX 3.3 3.366 25°C 3.168 3.3 3.432 Full range 3.135 25°C 5 5 25°C 4.8 4.75 VIN = 25 V, ILOAD = 0.2 A 25°C 11.76 12 12.24 15 V ≤ VIN ≤ 40 V, 0.2 A ≤ ILOAD ≤ 1 A 25°C 11.52 12 12.48 Full range 11.4 VIN = 30 V, ILOAD = 0.2 A 25°C 14.7 15 15.3 18 V ≤ VIN ≤ 40 V, 0.2 A ≤ ILOAD ≤ 1 A 25°C 14.4 15 15.6 Full range 14.25 15 15.75 25°C 1.217 1.23 1.243 25°C 1.193 1.23 1.267 Full range 1.18 8 V ≤ VIN ≤ 40 V, VOUT = 5 V, 0.2 A ≤ ILOAD ≤ 1 A LM2575-12 VIN = 15 V, ILOAD = 1 A LM2575-15 VIN = 18 V, ILOAD = 1 A 88 LM2575-ADJ VIN = 12 V, VOUT = 5 V, ILOAD = 1 A 77 Saturation voltage Maximum duty cycle ICL Peak current IL Output leakage current IQ Quiescent current ISTBY Standby quiescent current VIH (1) 25°C 50 Full range (3) (1) (2) VIN = 40 (4), Output = 0 V VIN = 40 (4), Output = –1 V (4) OFF (ON/OFF pin = 5 V) ON/OFF logic input level VIL ON (VOUT = nominal voltage) IIH OFF (ON/OFF pin = 5 V) OFF (ON/OFF pin = 0 V) % 100 nA 500 25°C 47 Full range 42 52 58 63 0.9 Full range OFF (VOUT = 0 V) ON/OFF input current 88 25°C 25°C IOUT = 1 A (2) V 1.28 77 VOUT = 5 V (ADJ version only) V 12.6 VIN = 12 V, ILOAD = 1 A VSAT 5.2 5.25 LM2575-05 Oscillator frequency 5.1 Full range VIN = 12 V, VOUT = 5 V, ILOAD = 0.2 A UNIT 3.465 4.9 75 fo (2) (3) (4) TYP 3.234 VIN = 12 V, ILOAD = 1 A Feedback bias current (1) TJ LM2575-33 IIB IIL MIN 25°C kHz 1.2 V 1.4 25°C 93 98 25°C 1.7 2.8 Full range 1.3 % 3.6 2 25°C A 4 7.5 30 mA 25°C 5 10 mA 25°C 50 200 µA 25°C 2.2 Full range 2.4 25°C 1.4 1.2 Full range 25°C 1 V 0.8 12 30 0 10 µA In the event of an output short or an overload condition, self-protection features lower the oscillator frequency to ∼18 kHz and the minimum duty cycle from 5% to ∼2%. The resulting output voltage drops to ∼40% of its nominal value, causing the average power dissipated by the IC to lower. Output is not connected to diode, inductor, or capacitor. Output is sourcing current. Feedback is disconnected from output and connected to 0 V. To force the output transistor off, FEEDBACK is disconnected from output and connected to 12 V for the adjustable, 3.3-V, and 5-V versions; and 25 V for the 12-V and 15-V versions. http://www.hgsemi.com.cn 4 2018 AUG LM2575 APPLICATION INFORMATION Layout Guidelines With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasitic inductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result in unwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated by heavy lines should be minimized. Optimal results can be achieved by single-point grounding (see Figure 2) or by ground-plane construction. For the same reasons, the two programming resistors used in the adjustable version should be located as close as possible to the regulator to keep the sensitive feedback wiring short. Fixed Output Voltage Versions FEEDBACK 4 +VIN LM2575-xx Fixed Output 1 OUTPUT 3 + GND VOUT 330 µH 2 VIN Unregulated DC Input L1 5 ON/OFF L O A D D1 CIN 100 µF + COUT 330 µF CIN = 100 µF, Aluminum Electrolytic COUT = 330 µF, Aluminum Electrolytic D1 = Schottky L1 = 330 µH Adjustable Output Voltage Versions +VIN 1 FEEDBACK 4 LM2575 (ADJ) OUTPUT 2 7-V to 60-V Unregulated DC Input L1 VOUT 330 µH R2 + CIN 100 µF 3 GND 5 ON/OFF D1 11DQ06 + L O A D COUT 330 µF R1 VOUT = VREF(1 + R2/R1) = 5 V Where, VREF = 1.23 V R1 = 2 k
R2 = 6.12 k
A. Pin numbers are for the KTT (TO-263) package. Figure 2. Test Circuit and Layout Guidelines http://www.hgsemi.com.cn 5 2018 AUG LM2575 APPLICATION INFORMATION (continued) Input Capacitor (CIN) For stability concerns, an input bypass capacitor (electrolytic, CIN ≥ 47 µF) needs to be located as close as possible to the regulator. For operating temperatures below –25°C, CIN may need to be larger in value. In addition, since most electrolytic capacitors have decreasing capacitances and increasing ESR as temperature drops, adding a ceramic or solid tantalum capacitor in parallel increases the stability in cold temperatures. To extend the capacitor operating lifetime, the capacitor RMS ripple current rating should be: I C,RMS  1.2( t on )I , where: T LOAD V ton  OUT {buck regulator}, and VIN T |VOUT| ton  {buck−boost regulator} (|V OUT|
V IN) T Output Capacitor (COUT) For both loop stability and filtering of ripple voltage, an output capacitor also is required, again in close proximity to the regulator. For best performance, low-ESR aluminum electrolytics are recommended, although standard aluminum electrolytics may be adequate for some applications. Based on the following equation: Output Ripple Voltage = (ESR of COUT) × (inductor ripple current) Output ripple of 50 mV to 150 mV typically can be achieved with capacitor values of 220 µF to 680 µF. Larger COUT can reduce the ripple 20 mV to 50 mV peak-to-peak. To improve further on output ripple, paralleling of standard electrolytic capacitors may be used. Alternatively, higher-grade capacitors such as “high frequency”, “low inductance”, or “low ESR” can be used. The following should be taken into account when selecting COUT: • At cold temperatures, the ESR of the electrolytic capacitors can rise dramatically (typically 3× nominal value at –25°C). Because solid tantalum capacitors have significantly better ESR specifications at cold temperatures, they should be used at operating temperature lower than –25°C. As an alternative, tantalums also can be paralleled to aluminum electrolytics and should contribute 10% to 20% to the total capacitance. • Low ESR for COUT is desirable for low output ripple. However, the ESR should be greater than 0.05 Ω to avoid the possibility of regulator instability. Hence, a sole tantalum capacitor used for COUT is most susceptible to this occurrence. • The capacitor’s ripple current rating of 52 kHz should be at least 50% higher than the peak-to-peak inductor ripple current. Catch Diode As with other external components, the catch diode should be placed close to the output to minimize unwanted noise. Schottky diodes have fast switching speeds and low forward voltage drops and, thus, offer the best performance, especially for switching regulators with low output voltages (VOUT < 5 V). If a high-efficiency, fast-recovery, or ultra-fast-recovery diode is used in place of a Schottky, it should have a soft recovery (versus abrupt turn-off characteristics) to avoid the chance of causing instability and EMI. Standard 50-/60-Hz diodes, such as the 1N4001 or 1N5400 series, are NOT suitable. Inductor Proper inductor selection is key to the performance-switching power-supply designs. One important factor to consider is whether the regulator will be used in continuous (inductor current flows continuously and never drops to zero) or in discontinuous mode (inductor current goes to zero during the normal switching cycle). Each mode has distinctively different operating characteristics and, therefore, can affect the regulator performance and requirements. In many applications, the continuous mode is the preferred mode of operation, since it offers greater output power with lower peak currents, and also can result in lower output ripple voltage. The advantages of continuous mode of operation come at the expense of a larger inductor required to keep inductor current continuous, especially at low output currents and/or high input voltages. http://www.hgsemi.com.cn 6 2018 AUG LM2575 APPLICATION INFORMATION (continued) The LM2575 can operate in either continuous or discontinuous mode. With heavy load currents, the inductor current flows continuously and the regulator operates in continuous mode. Under light load, the inductor fully discharges and the regulator is forced into the discontinuous mode of operation. For light loads (approximately 200 mA or less), this discontinuous mode of operation is perfectly acceptable and may be desirable solely to keep the inductor value and size small. Any buck regulator eventually will operate in discontinuous mode when the load current is light enough. The type of inductor chosen can have advantages and disadvantages. If high performance/quality is a concern, then more-expensive toroid core inductors are the best choice, as the magnetic flux is contained completely within the core, resulting in less EMI and noise in nearby sensitive circuits. Inexpensive bobbin core inductors, however, generate more EMI as the open core will not confine the flux within the core. Multiple switching regulators located in proximity to each other are particularly susceptible to mutual coupling of magnetic fluxes from each other’s open cores. In these situations, closed magnetic structures (such as a toroid, pot core, or E-core) are more appropriate. Regardless of the type and value of inductor used, the inductor never should carry more than its rated current. Doing so may cause the inductor to saturate, in which case the inductance quickly drops, and the inductor looks like a low-value resistor (from the dc resistance of the windings). As a result, switching current rises dramatically (until limited by the current-by-current limiting feature of the LM2575) and can result in overheating of the inductor and the IC itself. Note that different types of inductors have different saturation characteristics. Output Voltage Ripple and Transients As with any switching power supply, the output of the LM2575 will have a sawtooth ripple voltage at the switching frequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth ripple current and the ESR of the output capacitor (see note on COUT). Furthermore, the output also may contain small voltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch and the parasitic inductance of COUT. These voltage spikes can be minimized through the use of low-inductance capacitors. There are several ways to reduce the output ripple voltage: a larger inductor, a larger COUT, or both. Another method is to use a small LC filter (20 µH and 100 µF) at the output. This filter can reduce the output ripple voltage by a factor of 10 (see Figure 2). Feedback Connection For fixed voltage options, FEEDBACK must be wired to VOUT. For the adjustable version, FEEDBACK must be connected between the two programming resistors. Again, both of these resistors should be in close proximity to the regulator, and each should be less than 100 kΩ to minimize noise pickup. ON/OFF Input ON/OFF should be grounded or be a low-level TTL voltage (typically