LM2675M-12

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1. Describe

The LM2675M-12 series of regulators are monolithically integrated DC-DC converter circuits built on the LMDMOS process. These regulators provide all the active functions of a step-down (buck) switching regulator capable of driving 1A load current with excellent line and load regulation. The devices are available in fixed output voltages of 3.3 V, 5 V, 12 V, and adjustable output versions. These regulators require a minimal number of external components, are simple to use and include patented internal frequency compensation and fixed frequency oscillators. The LM2675M-12 series operates at a switching frequency of 260 kHz, thus allowing the use of smaller filter components than are required for low frequency switching regulators. Due to its very high efficiency (>90%), the copper traces on the printed circuit board are the only heat sinks required. This feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in the datasheet is a selection guide for diodes and capacitors designed for switch-mode power supplies. Additional features include ±1.5% tolerance of output voltage at specified input voltage and output load conditions, and ±10% of oscillator frequency. Includes external shutdown with typical 50µA standby current. The output switch includes current limit and thermal shutdown for full protection under fault conditions.

2. Feature

    1. Efficiency up to 96%

    2. Available in 8-Pin SOIC, PDIP, and 16-Pin WSON Packages

    3. Only 5 external components required

    4. 3.3V, 5V, 12V and adjustable output versions

    5. Adjustable version output voltage range: 1.21 V to 37 V

    6. Maximum output voltage tolerance at line and load conditions is ±1.5%

    7. Guaranteed 1A output load current

    8. Wide input voltage range: 8 V to 40 V

    9. 260kHz fixed frequency internal oscillator

  10. TTL shutdown capability, low power standby mode

  11. 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. Function description

The voltage regulation loop in the LM2675M-12 regulates the output voltage by keeping the voltage on the FB pin (VFB) the same as the internal REF voltage (VREF). A resistor divider pair is required to program the ratio from the output voltage VOUT to VFB. A resistor is connected from VOUT of the LM2674 to ground and the midpoint is connected to the FB pin. The voltage reference system produces an accurate voltage reference over the entire temperature range. The internal REF voltage is typically 1.21 V. To program the output voltage of the LM2675M-12 to a specific value VOUT, R1 can be calculated with R2 selected. The recommended range for R2 for most applications is 10 kΩ to 100 kΩ. If the resistor divider is connected incorrectly, the output voltage cannot be regulated due to a damaged feedback loop. If the FB pin is shorted to ground, the output voltage is driven close to VIN because the regulator sees a very low voltage on the FB pin and tries to regulate it. In this case, the load connected to the output may be damaged. Do not short the FB pin to ground when the LM2675M-12 is enabled. It is important to route feedback traces away from noisy areas of the PCB.

7. Application Information

The LM2675M-12 is a step-down DC-DC regulator. This device is typically used to convert higher DC voltages to lower DC voltages with a maximum output current of 1 A. The following design process can be used to select components for the LM2675M-12. When the output voltage is greater than about 6 V and the duty cycle at the minimum input voltage is greater than about 50%, the designer should choose the output filter carefully Element. Large hysteresis in current limit may be observed 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.