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1. Describe
The LM2674M-ADJ/NOPB series of regulators are monolithic integrated circuits built on the LMDMOS process. These regulators provide all the active functions of step-down (buck) switching regulators capable of driving 500 mA load current and load regulation with excellent line driving. These devices are available in fixed output voltages of 3.3 V, 5 V, 12 V and adjustable output versions. Requiring a minimum number of external components, these regulators are simple to use and include patented internal frequency compensation and a fixed frequency oscillator. The LM2674 series operates at a switching frequency 260 kHz, allowing smaller filter components than required for lower frequency switching regulators. Due to its very high efficiency (>90%), the copper traces on the printed circuit board are the only heat sink required. A range of standard inductors for use with the LM2674M-ADJ/NOPB are available from several different manufacturers. This feature greatly simplifies the design of advanced integrated circuits using these switch-mode power supplies. Also included in the datasheet are selector guides for diodes and capacitors designed to Operates in switch mode power supplies.
2. Feature
1. Efficiency up to 96%
2. Available in 8-pin SOIC, PDIP and 16-pin WSON packages
3. Simple and easy to use design
4. Only 5 external components required
5. Use off-the-shelf standard inductors
6. 3V, 5V, 12V and adjustable output versions
7. Adjustable version output voltage range: 1.21 V to 37 V
8. Maximum output voltage tolerance at line and load conditions is ±1.5%
9. Guaranteed 500mA output load current
10. 0.25-Ω DMOS output switch
11. Wide input voltage range: 8 V to 40 V
12. 260kHz fixed frequency internal oscillator
13. TTL shutdown capability, low power standby mode
14. Thermal shutdown and current limit protection
3. Application
1. Simple high efficiency (>90%) step-down (Buck) regulator
2. High Efficiency Preregulators for Linear Regulators
3. Positive and negative converter
4. Pin configuration
5. Pin Description
6. Application Information
The LM2674M-ADJ/NOPB is a step-down DC-DC regulator. It is typically used to convert a higher DC voltage to a lower DC voltage with a maximum output current of 0.5 A. The following design procedure can be used to select the components of the LM2674M-ADJ/NOPB. Alternatively, WEBENCH® software can be used to generate a complete design. When generating designs, WEBENCH software uses an iterative design process and accesses a comprehensive component database. When the output voltage is greater than about 6 V, the duty cycle at the minimum input voltage is greater than about 50%, and the designer must choose the output filter components carefully. Large hysteresis may be observed in current limit when an application designed for these specific operating conditions encounters a current limit fault condition. This affects the output voltage of the device until the load current decreases enough for the current limit protection circuit to reset itself. If the output capacitor is large enough, it is possible that as the output tries to recover, the output capacitor charging current is large enough to be fully resolved by repeatedly retriggering the current limit circuit before the output. This is exacerbated by higher output voltage settings, as the output capacitance varies with the square of the output voltage (½ CV2), requiring an increase in charging current. A simple test to determine if this may be the case for a suspect application is to apply a short across the converter's output, then remove the shorted output condition. With the selection of external components in the appropriate application, the output returns to smooth. Practical External Components Experimentally found to work well under these specific operating conditions are COUT = 47 µF, L = 22 µH.
