LM3481MMX/NOPB IC

Technical Specifications of LM3481MMX/NOPB

Datasheet	LM3481MMX/NOPB datasheet
Category	Integrated Circuits (ICs)
Family	PMIC – Voltage Regulators – DC DC Switching Controllers
Manufacturer	Texas Instruments
Series	–
Packaging	Tape & Reel (TR)
Part Status	Active
Output Type	Transistor Driver
Function	Step-Up, Step-Up/Step-Down
Output Configuration	Positive
Topology	Boost, Flyback, SEPIC
Number of Outputs	1
Output Phases	1
Voltage – Supply (Vcc/Vdd)	2.97 V ~ 40 V
Frequency – Switching	100kHz ~ 1MHz
Duty Cycle (Max)	85%
Synchronous Rectifier	No
Clock Sync	Yes
Serial Interfaces	–
Control Features	Enable, Frequency Control, Ramp, Soft Start
Operating Temperature	-40°C ~ 125°C (TJ)
Package / Case	10-TFSOP, 10-MSOP (0.118″, 3.00mm Width)
Supplier Device Package	10-VSSOP

Description for the LM3481

As a low-side N-FET controller, the LM3481 has a high level of performance and is flexible enough to be used in switching regulators. The part can be used in circuits that need a low-side FET, like boost, fly back, SEPIC, and a number of other similar designs. By running the LM3481 device at very high switching frequencies, which is possible, the size of the solution as a whole can be reduced.

By utilizing a single external resistor or synchronizing it to an external clock, the switching frequency of the LM3481 can be set to any number between 100kHz and 1MHz. This range of values is called the operating range of the LM3481. Current mode control not only limits the amount of current from cycle to cycle, but it also gives you a wider bandwidth and better response to sudden changes. You only need a single resistor on the outside to set the current limit.

The LM3481 component has several layers of protection, such as thermal shutdown, protection against short circuits, and protection against overvoltage. In power-saving shutdown mode, the total supply current is reduced to 5 A, which lets the power supply work in steps. An internal soft-start system controls the current flow when the machine starts up.

Features for the LM3481

• LM3481QMM are qualified for AEC-Q100 Grade 1 (operating junction temperature of –40°C to +125°C) and are made for use in cars.
• VSSOP package with 10 leads.
• The internal push-pull driver can handle up to 1 A of peak current.
• Current Limit and Shutdown When Too Hot.
• You can get the best frequency compensation with a capacitor and a resistor.

Applications

• Automotive Start-Stop Applications.
• Automotive ADAS Driver Information.
• Set-Top Boxes
• Boost for Audio Amplifiers

Detailed Description

The LM3481 component uses a fixed frequency, Pulse Width Modulated (PWM), and pulsed current mode control architecture. An external sense resistor is often part of an application circuit. This resistor measures the peak current going through an external MOSFET. The voltage made across this resistor is sent to the ISEN pin. After that, a level shift is done, and the resulting voltage is sent to the PWM comparator’s positive input. A voltage divider composed of external resistors monitors the output voltage, which is then sent to the negative input of the error amplifier (EA) (feedback pin, FB).

After the output of the error amplifier on the COMP pin is added to the slope correction ramp, it is sent to the negative input of the PWM comparator. The oscillator uses the SET/Blank-out and switches logic blocks to initialize the RS latch at the beginning of each switching cycle. Because of this, the DR pin, the gate of the external MOSFET, has to get a high signal. This turns on the MOSFET on the outside. When the PWM comparator’s positive input voltage exceeds its negative input voltage, the MOSFET outside is disabled, and the RS latch is reset.

Most of the time, when you measure the voltage across the sense resistor, you’ll see noise spikes that aren’t real. These spikes could force the PWM comparator to reset the RS latch before it should. Inside the integrated circuit is a blank-out circuit, whose duty is to keep the latch from being briefly reset by the PWM comparator after the latch has been set. This is done so that spikes won’t turn the latch off.

When there is either a very light or no load, more energy is sent to the output capacitor than to the load when the external MOSFET is active during the blank-out time. The LM3481 has a built-in overvoltage comparator that checks the voltage at the feedback pin (FB pin) and stops the output voltage from going up when this happens. To do this, you have to reset the RS latch. The latch will stay in the reset state until the output has dropped to a normal level. As a result, the working frequency drops when the load is light. This makes the machine very efficient.

Feature Description

Safety from Too Much Voltage The output voltage of the LM3481 has OVP, which stands for “overvoltage protection.” OVP is measured and written down at the feedback pin (FB). When the voltage at the feedback pin goes up by more than VFB + VOVP, OVP is triggered.

The power MOSFET will turn off when the drive pin, also called DR, goes low because of OVP. When the MOSFET is turned off, the voltage at the output will go down. The LM3481 will switch again when the feedback voltage reaches VFB + (VOVP – VOVP(HYS)).

● Bias Voltage

Either the LM3481’s internal bias comes from the internal bias voltage generator, shown in the block diagram, or the LM3481’s internal bias comes directly from the voltage at the VIN pin. When the input voltage exceeds 6 V, the LM3481’s internal bias voltage generator takes over and provides the bias. When the input voltage is less than 6 V, the internal IC bias is the input voltage. The voltage for the gate driver is sent out to the VCC pin, so an external capacitor with a value between 0.47 F and 4.7 F can be used to adjust it (depending on the requirements of the FET). Using a voltage source from the outside is not a good idea to try to bias the VCC pin.

● Short-Circuit Protection

If the voltage measured on the ISEN Pin, next to the sensing resistor, is more than 220 mV, the short-circuit current restriction will be turned on. The LM3481 has a comparator that slows the switching rate by a factor of eight when it finds a short. It stays like this until the short is removed, at which point it goes back to how it was before.

Device Functional Modes

After the input voltage rises above the UVLO threshold, the device is programmed to begin operating at the frequency determined by the pull-down resistor on the FA/SYNC/SD pin or by the waveform applied to the FA/SYNC/SD pin. The LM3481 will power down if the FA/SYNC/SD pin is pulled high.

Application Information

The LM3481 can either work in a continuous or discontinuous conduction mode. For always-on conduction operation, the following software was made. This mode of operation is more efficient and causes less EMI interference than the discontinuous mode.

● Design Requirements

The designer needs to know the range of input voltage, output voltage, output current range, and switching frequency needed for the application. These four main parameters will affect which parts can be used to make the system work right.

Power Supply Recommendations

The LM3481 can work from a number of different DC power sources, including a car battery. In that case, the VIN input should be protected from voltage reverse and voltage dumps that are higher than 48 volts. It is very important that the impedance of the input supply rail is low enough so that a sudden change in the input current does not cause the level to drop below that of the VIN UVLO. If long cables connect the input supply and the usual input capacitor, there may be a need for more bulk capacitance.

Conclusion

In conclusion, the LM3481 is a flexible and efficient low-side N-FET controller with various features and protection mechanisms that make it a good choice for a wide range of topologies. Its high switching frequencies and ability to control current mode make it a great component for start-stop systems in cars, portable devices, offline power supplies, and audio amplifiers.

If you want to order the LM3481 or learn more about it, contact ICRFQ, the best electronic distributor in China, to get the best products at a fair price. Don’t be afraid to use the LM3481 to take your designs to the next level by taking advantage of this great part.

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