LM2675MX-ADJ/NOPB

LM2675MX-ADJ/NOPB

Part Number: LM2675MX-ADJ/NOPB

Manufacturer: Texas Instruments

Description: IC REG BUCK ADJUSTABLE 1A 8SOIC

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LM2675MX-ADJ/NOPB Description

The monolithic integrated DC-DC converter circuits in the LM2675 family of regulators were created using the LMDMOS manufacturing process. These regulators provide all of the active operations necessary for a step-down (buck) switching regulator, which can drive a 1-A load current with excellent line and load regulation. These devices have 3.3 V, 5 V, and 12 V fixed output voltages and an adjustable output version.

These regulators are easy to operate, need minimal external components, and have patented internal frequency adjustment and a fixed frequency oscillator. Because the LM2675 series switches at 260 kHz, fewer filter components are possible than switching regulators operating at lower frequencies. The copper traces on the printed-circuit board are the only heat sinking because of its extremely high efficiency (>90%).

LM2675MX-ADJ/NOPB Features

  • The efficiency of 96% or more.
  • Accessible in 16-Pin WSON Package, PDIP, and 8-Pin SOIC packages.
  • It only needs five external components.
  • Versions include 3.3-V, 5-V, 12-V, and Adjustable Output.
  • 1 A output load current was guaranteed.
  • Fixed Frequency Internal Oscillator at 260 kHz.
  • Low-Power Standby Mode and TTL Shutdown Capability
  • Protection from current limits and thermal shutdown.

LM2675MX-ADJ/NOPB Applications

  • Simple High Efficiency (>90%) Step-Down (Buck) Regulator
  • Efficient Preregulator for Linear Regulators
  • Positive-to-Negative Converter

Detailed Description

Overview

To implement a step-down (buck) switching regulator, the LM2675 contains all of the necessary active functionalities. DMOS power MOSFETs are used as the internal power switch because of their excellent efficiency and large current capacity (up to 1 A) in power supply designs. The LM2675 is a power converter that was designed to be as simple to use as possible. Complete designs often call just a handful of external parts from known vendors. This data sheet and the TI WEBENCH® design tool make creating a fully functional switching power supply easy.

Feature Description

● Adjustable Output Voltage

By keeping the voltage on the FB pin (VFB) equal to the internal REF voltage, the LM2675’s regulation loop ensures a consistent and stable output voltage (VREF). It is possible to customize the ratio of VOUT to VFB via a resistor divider. The LM2674’s VOUT is linked to the ground via the resistor, and the FB pin is connected to the resistor’s midpoint. The voltage reference system generates a stable voltage standard independent of environmental conditions. The standard REF voltage inside is 1.21 V. Calculating R1 with a chosen R2 sets the output voltage of the LM2675 to the value VOUT that was programmed.

For a common use of the variable output voltage, please refer to the Programming Output Voltage section. In most cases, 10 k to 100 k is the sweet spot for R2. An improperly connected resistor divider breaks the feedback loop, rendering voltage regulation impossible. Since the regulator will attempt to regulate the very low voltage it perceives on the FB pin if it is shorted to ground, the output voltage will be driven close to VIN. The connected load to the output could be harmed in such a scenario. When the LM2675 is active, you must avoid connecting the FB pin to the ground. The feedback trace needs to be removed if there is a noisy spot on the PCB.

Device Functional Modes

● Shutdown Mode

To turn the LM2674 on and off electrically, use the ON/OFF pin. If the pin’s voltage drops below 1.4 V, the gadget will power down. Typically, this mode draws 20 A while on standby.

● Active Mode

The gadget switches on, and the output voltage climbs over the typical regulating level whenever the ON/OFF pin’s voltage reaches more than 1.4 V.

Application Information

There is a step-down DC-DC regulator called the LM2675. Common applications include reducing a greater DC voltage to a lower DC voltage, with a maximum output current of 1 A. Following is a design technique that can be used to choose LM2675 components. Careful consideration must be given to selecting the output filter components when the output voltage is larger than about 6 V and the duty cycle at minimal input voltage is greater than 50%. A considerable hysteresis in the current limit may be seen when an application optimized for these conditions is subjected to a fault state that exceeds the current limit. If the load current is too high, the current limit protection circuit may trip, lowering the device’s output voltage until the current is low enough to reset.

The LM2675 is intended to behave as follows when subjected to the current set of constraints:

Under the existing conditions, the LM2675 is expected to act as follows:

  1. As soon as the current in the inductor approaches the current limit level, the ON-pulse is abruptly cut off. Any imaginable scenario involving an application will result in this.
  2. The inductor can become saturated due to subharmonic oscillations; the current limit block is built to lower the duty cycle to below 50% to prevent this from happening.
  3. As soon as the inductor current drops below the current limit threshold, a brief period of relaxation occurs. The duty cycle gradually increases beyond 50% to the value needed to achieve control.

If the output capacitance is sufficiently high, that is another story. If so, the output capacitor charging current might be too high to prevent the output from fully stabilizing before the current limit circuit is repeatedly triggered. Because the output capacitor’s energy needs vary with the square of the output voltage (1/2 CV2), increasing the output voltage worsens this problem. Applying a short circuit across the converter’s output and clearing the shorted situation is a straightforward way to test for the presence of this issue in a potentially affected application.

When using well-chosen external components, the output of an application can recover smoothly after an error. Experiments have shown that COUT = 47 F and L = 22 H are good values for the exterior components under these conditions. Notably, even with these components, the maximum load current for a device with an ICLIM current limit is ICLIM/2 to avoid the possibility of the enormous current limit hysteresis.

For a maximum current of 1.5 A, for instance, it is essential to verify that the current limit of the selected switcher is at least 3 A if the input is 24 V and the configured output voltage is 18 V. The LM2675 uses frequency foldback in conjunction with the current limit in the event of a severe overcurrent or short-circuit. If the inductor current during any given cycle exceeds the current limit level, the switching frequency will drop to protect the integrated circuit. In the event of a severe short circuit, the frequency drops below 100 kHz.

Conclusion

Several manufacturers make LM2675-compatible standard inductors. These sophisticated ICs simplify switch-mode power supply design. The data sheet includes switch-mode power supply diode and capacitor choice recommendations. ±1.5% output voltage tolerance and ±10% oscillator frequency tolerance is also available. External shutdown includes 50-μA standby current. Current limiting and thermal shutdown safeguard the output switch from faults.

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