LM22675MRX-5.0 IC

Technical Specifications of LM22675MRX-5.0/NOPB

Datasheet	LM22675MRX-5.0/NOPB datasheet
Category	Integrated Circuits (ICs)
Family	PMIC – Voltage Regulators – DC DC Switching Regulators
Manufacturer	Texas Instruments
Series	SIMPLE SWITCHER?
Packaging	Tape & Reel (TR)
Part Status	Active
Function	Step-Down
Output Configuration	Positive
Topology	Buck
Output Type	Fixed
Number of Outputs	1
Voltage – Input (Min)	4.5V
Voltage – Input (Max)	42V
Voltage – Output (Min/Fixed)	5V
Voltage – Output (Max)	–
Current – Output	1A
Frequency – Switching	500kHz
Synchronous Rectifier	No
Operating Temperature	-40°C ~ 125°C (TJ)
Mounting Type	Surface Mount
Package / Case	8-PowerSOIC (0.154″, 3.90mm Width)
Supplier Device Package	8-SO PowerPad

Description for the LM22675

The LM22675 switching regulator offers all the capabilities required to create an effective high voltage step-down (buck) regulator with the least amount of external parts. This simple regulator features a 42 V N-channel MOSFET switch that can supply up to 1 A of load current. High efficiency (> 90%) is a feature, as well as excellent line and load regulation. The input to output voltage ratio can be as wide as possible with voltage mode control, which has a short minimum on-time.

The user is relieved of the laborious chore of computing the loop compensation components thanks to internal loop compensation. There are options for a fixed 5 V output and an adjustable output voltage. Small exterior components and a good transient response are made possible with a switching frequency of 500 kHz. A precise enable input enables regulator control and system power sequencing to be simplified. The regulator only draws 25 A when it is in shutdown mode (typ). Internal soft-start (typically 500 s) protects external components. Additionally, the LM22675 has built-in current limiting and thermal shutdown to guard against unintentional overloads.

The SIMPLE SWITCHER® family of devices from Texas Instruments includes the LM22675. Using a minimal amount of external components and the TI WEBENCH design tool, the SIMPLE SWITCHER idea enables an intuitively usable comprehensive design. The WEBENCH tool from TI has capabilities including Build-It boards for simple design-in, electrical simulation, thermal simulation, and external component computation.

Features for the LM22675

• 5 V to 42 V, a broad input voltage range.
• Internal compensation for the voltage mode control.
• Low ESR ceramic capacitors are stable.
• N-Channel MOSFET with a 200 m.
• Operating Junction Temperature Range: 500 kHz Switching Frequency, -40°C to 125°C
• Precision Fully enable the integrated boot-strap diode and the integrated soft-start pin. Step-Down and Inverting Buck-Boost Applications with WEBENCH® Support
• Automotive Grade Product LM22675Q (-40°C to +125°C Operating Junction Temperature) is AEC-Q100 Grade 1 Qualified.
• SO PowerPAD-8 (Exposed Pad) Set

Detailed Description

Overview

The voltage mode constant frequency PWM architecture used by the LM22675 is implemented. Input voltage feedforward is additionally utilized to maintain the loop gain against input voltage changes. This makes it possible to adjust the loop compensation for transient performance. A rectangular waveform that swings from around zero volts to VIN is produced at the switch pin by the power MOSFET and diode. This waveform is averaged by the output capacitor and inductor to produce the output voltage of the regulator.

This waveform’s duty cycle can be changed to regulate the output voltage. The duty cycle is changed by the error amplifier to maintain the output at the desired level by comparing the output voltage to an internal reference. For outputs of 5 V and lower, the internal loop compensation of the -ADJ option is optimized. The -5.0 option can be used in conjunction with an external voltage divider if an output voltage of 5 V or more is required. The minimum output voltage is 1.285 V, which is the same as the reference voltage (typ).

Feature Description

UVLO and Precision Enable The regulator is managed by precision enable input (EN). A resistor divider from another source can be used with the precision feature to easily sequence several power supplies. The regulator will be disabled if this pin is connected to either ground or a voltage lower than 1.6 V (typical). At an input voltage of 12 V, the current drain from the input supply is 25 A (typ). An internal pullup of about 6 A exists at the EN input.

In order to activate the regulator, this pin can either be pulled to a voltage greater than 2.2 V (typ) or left floating. This input has hysteresis that is roughly 0.6 V (typ) higher than the 1.6 V (typ) threshold. The voltage applied to the enable input must never go over the pin’s absolute maximum specification of 6 V.

Even though the EN pin has an inbuilt pullup, it is best to pull the input high when not using this feature, especially in loud surroundings. The easiest way to accomplish this is by adding a resistor between VIN and the EN pin. The inbuilt zener diode at the EN pin will conduct at voltages above roughly 6 V, hence the resistor is necessary.

The current through this zener must be limited to no more than 100 A. A resistor of 470 k will safely limit the current for input voltages as high as 42 V. At lower input voltages, smaller resistor values can be utilized.  The LM22675 device also incorporates an input undervoltage lock-out (UVLO) feature. The regulator won’t operate if the input voltage is insufficient to appropriately bias the internal circuitry, as a result. The falling threshold is 3.9 V, and the rising threshold is 4.3 V (typ) (typ).  In some cases these thresholds may be too low to provide good system performance. The solution is to use the EN input as an external UVLO to disable the part when the input voltage falls below a lower boundary. This is frequently used to stop early start-up or excessive battery drain.

● Soft-Start

The regulator may gradually attain steady-state functioning thanks to the soft-start functionality, decreasing start-up pressures. The output voltage rises thanks to the inherent soft-start feature in roughly 500 s. This time cannot be modified because it is fixed. Any time the part is turned off or a thermal overload event takes place, soft-start is reset.

● Boot-Strap Supply

To regulate the power MOSFET, the LM22675 has a floating high-side gate driver. The external boot-strap capacitor located between the SW and BOOT pins serves as the driver’s power source. To these pins, short, wide PCB traces must link a high-quality 10 nF ceramic capacitor. The regulator sets a minimum off-time requirement in part to make sure that this capacitor recharges after each switching cycle. For the boot-strap capacitor to properly recharge in the shortest amount of off-time, a minimum load of approximately 5 mA is needed. If employed, the output voltage divider can supply some of this load.

Conclusion

The operating voltage supply range for the LM22675 is between 4.5 V and 42 V. This input supply needs to be tightly controlled, able to handle the highest input current, and able to maintain a steady voltage. The input supply rail’s resistance needs to be low enough so that an input current transient won’t result in a significant enough reduction in LM22675 supply voltage to trigger a false UVLO fault and force a system reset. In addition to the ceramic bypass capacitors, more bulk capacitance may be needed if the input supply is placed farther away from the LM22675 than a few inches. A 47 F or 100 F electrolytic capacitor is a common option; however the amount of bulk capacitance is not crucial.

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