Part Number: LMD18245T/NOPB

Manufacturer: Texas Instruments

Description: IC MTR DRV BIPLR 12-55V TO220-15

Shipped from: Shenzhen/HK Warehouse

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LMD18245T Overview

A 3A 55V DMOS full-bridge motor driver, the LMD18245T can drive and regulate a brushed DC motor or one phase of a bipolar stepper motor. The LMD18245T is constructed utilizing a multi-technology method incorporating DMOS power switches, CMOS control and protection circuitry, and bipolar control and protection circuitry on a single monolithic structure. It uses a set off-time chopper approach to control motor current.

LMD18245T Function Description

All of the circuitry needed to construct a fixed off-time chopper amplifier is present in the LMD18245 chip. These parts include a full H-bridge with clamp diodes made entirely of DMOS, an amplifier for detecting load current, a comparator, a monostable, and a DAC for controlling the chopping threshold digitally. Additionally included are logic, level shifting, and drive blocks enabling digital control of the load current’s direction and braking.

Circuit 9’s chopper amplifiers use feedback-driven switching of a power bridge to regulate and cap the amount of current flowing through a motor’s winding. Four solid-state power switches and diodes are connected in an H pattern to form the bridge.

The control circuitry (not illustrated) keeps track of the winding current and compares it to a threshold. A source and sink switch in the opposing portions of the bridge drives the supply voltage over the winding while the winding current is below the threshold, causing the winding current to grow towards VCC/R (circuits 9a and 9d) quickly. The control circuitry disables the sink switch for a set time when the winding current exceeds the threshold.

The source switch and the opposing top diode short the winding during the off-time (circuits 9b and 9e), causing the winding current to recirculate and eventually decay to zero. The winding current rapidly climbs toward VCC/R as the control circuitry turns the sink switch back ON at the end of the off-time (again, circuits 9a and 9d). The previous sequence is repeated to generate a current chopping action that limits the winding current to the threshold (circuit 9g).

Only when the winding current reaches a specific level can chopping take place. When the winding current switches direction (circuits 9c and 9f), the diodes offer a declining path for the initial winding current. This kind of chopper amplifier is also called a fixed off-time chopper since the bridge shorts the winding for a set amount of time.

The LMD18245 Chopper Amplifier

All the circuitry required to construct a fixed off-time chopper amplifier is included in the LMD18245 device. These building components consist of a full H-bridge with clamp diodes composed of DMOS transistors, an amplifier for detecting the load current, a comparator, a monostable, and a DAC for digitally controlling the chopping threshold. Drive blocks, level shifting, and logic are also included for digital control of the load current’s direction and braking.

BRIDGING THE H Four DMOS power switches and their corresponding body diodes are coupled in an H-bridge configuration to form the power stage.

In this scenario, the motor windings, the time constant to charge or discharge each inductor is given as:

τ = L/R


  • L is the winding inductance
  • R is the sum of the series resistance in the current path, including the winding resistance

When both source and sink switches are turned ON in the bridge’s opposing halves, the whole supply voltage (I x RDS(ON)) is forced across the motor winding. The winding current grows exponentially while the bridge is in this state, reaching a limit set by the supply voltage, the switch drops (I x RDS(ON)), and the winding resistance. However, the current chopping circuitry will start to operate after the exponential growth rate in the winding current stops.

When the sink switch is turned off, a voltage transient results, which forward biases the body diode of the other source switch. While holding the transient at one diode drop over the supply voltage, the diode provides an alternative current route. The winding current practically shorts out while the bridge is in this state, recirculating and degenerating exponentially at a rate determined by the L/R time constant. Both the switches and the body diodes offer a degradation route for the initial winding current during a change in the direction of the current.

Numerous factors can affect the performance and behavior of the motor windings during actual motor operation. Only a few examples include resonance, friction, eddy currents, motor loads, temperature coefficients, and damping of the windings. All of these problems are outside the purview of this data sheet.

The Current Sense Amplifier

The DMOS power switches are made up of several parallel transistor cells. The current sense amplifier offers a distinct, low-loss method for sensing the load current by utilizing a tiny portion of the cells of both upper switches. In reality, each upper switch simultaneously serves as a 1x sense device and a 4000x power device. The devices divide the total drain current in proportion to the 1:4000 cell ratio because the current sense amplifier compels the voltage at the source of the sensing device to equal that at the source of the power device.

The output of the current sensing amplifier only detects forward current, or current flowing from drain to source. As a result, the power bridge’s upper two switches conduct 250 A per amp of total forward current through the current sense amplifier. According to the load current, the sense current creates a potential across RS that is proportionate to it; for instance, for every amp of load current, the sense current creates a potential of one volt across a 4 k resistor (the sum of 250 A per amp and 4 k).

RS sets the gain of the chopper amplifier because the load current is chopped as soon as the voltage at CS OUT exceeds the threshold; for instance, a 2 k resistor sets the gain at two amps of load current per volt of the threshold (the reciprocal of the product of 250 A per amp and 2 k).

A quarter-watt resistor will do. Switching noise is removed from the current sense signal by a low-value capacitor linked in parallel with RS. The operational voltage range at CS OUT is indicated to be 0V to 5V, even though the maximum DC voltage compliance at that location is 12V.


As a result, the LMD18245T is a trustworthy and adaptable DMOS full-bridge motor driver that can successfully drive and manage the current in your brushed DC motor or one phase of a bipolar stepper motor. It provides the circuits to build a fixed off-time chopper amplifier and a fixed off-time chopper approach to control motor current. The LMD18245T is a perfect solution for various motor applications thanks to its effective power stage, logic, level shifting, and drive blocks for digital control.

Our team of experts at ICRFQ is always available to help you if you’re interested in buying the LMD18245T or have any concerns about its features. We provide electrical parts that are both affordable and of the highest quality, as well as professional guidance to assist you to find the parts you require for your project. Therefore, don’t hesitate to contact us immediately, and let us provide you with the assurance you need to begin working on your project!

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