Texas Instruments LM3813MX-7.0

Overview

LM3813MX-7.0 from Texas Instruments is a precision low-side current gauge IC featuring an integrated 0.004Ω sense element, ±7A continuous sensing range, PWM output encoding current magnitude and direction, and 50 ms sampling interval. It delivers ±2% room-temperature accuracy and operates from 2V to 5.25V supply, enabling real-time battery discharge monitoring in portable power systems.

For engineers reviewing the LM3813MX-7.0 datasheet, LM3813MX-7.0 pinout, LM3813MX-7.0 application, or LM3813MX-7.0 equivalent, key selection criteria include low-side sensing topology, PWM interface compatibility with microcontrollers, thermal layout sensitivity for 7A accuracy, shutdown quiescent current (2.5 µA), and D0008A SOIC-8 package constraints.

Technical Context

The LM3813MX-7.0 implements a delta-sigma analog-to-digital converter with digital filtering to average sensed current over 50 ms intervals, rejecting transient spikes while maintaining DC accuracy. Its PWM output encodes bidirectional current via duty cycle (50% = zero, >50% = positive, <50% = negative), with quantization resolution of 1/1024 and inherent 0.5-bit offset requiring correction for sub-11 mA precision.

Internal architecture integrates the sense resistor into the lead frame with 2600 ppm/°C temperature coefficient; accuracy at ±7A depends critically on copper area under pins 1 and 2 to manage thermal gradients. The device uses internal power-on-reset and accepts shutdown control via TTL-compatible SD pin (V_TH = 1.8 V, V_TL = 0.7 V).

Key Specifications

Pinout & Package

LM3813MX-7.0 is housed in an 8-pin SOIC package (D0008A) with exposed pad for thermal enhancement. Pin 1 serves dual function as SENSE+ and GND; Pin 8 is VDD. Ground connections occupy Pins 7 and 8 (VDD) in low-side configuration, requiring careful PCB copper pour under sense pins to minimize thermal error at 7A.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-sensing applications.

Compared with INA240A1 and ACS724LLCTR-10AU-T, the LM3813MX-7.0 uniquely combines ultra-low-loss low-side sensing, built-in 50 ms averaging for noise immunity, and direct PWM interface - eliminating signal conditioning and reducing firmware complexity in cost-sensitive 3.3/5 V embedded systems.

Availability

LM3813MX-7.0 is available at Aetrix Electronics and suitable for battery charge/discharge gauge, motion control diagnostics, and resettable smart fuse applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM3813MX-7.0 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company specializing in analog and embedded processing technologies, with decades of leadership in precision data converters and power management ICs.

The LM3813MX-7.0 belongs to TI's precision current-sense gauge product line, engineered specifically for low-loss, microcontroller-friendly current monitoring in portable, battery-powered, and industrial control systems.

FAQ

What is the sensing topology supported by the LM3813MX-7.0?

The LM3813MX-7.0 is designed exclusively for low-side current sensing, where the device is placed between the load and system ground. Pin 1 (SENSE+, GND) connects to ground, and Pin 2 (SENSE−) connects to the load return path. This configuration avoids high-voltage common-mode challenges but requires attention to ground path integrity and thermal layout under pins 1 and 2 to maintain ±2% accuracy at ±7A.

How does the PWM output of the LM3813MX-7.0 encode current magnitude and direction?

The LM3813MX-7.0 outputs a 20 Hz PWM waveform where duty cycle linearly represents sensed current: 50% = 0 A, 95.5% = +7 A, and 4.5% = −7 A. The relationship follows I_SENSE = 2.2 × (D − 0.5) × 7 A, with D as measured duty cycle. A 0.5-bit quantization offset (≈11 mA error) must be subtracted from D for highest precision, as documented in the TI SNOS028D datasheet.

What is the recommended PCB layout practice to achieve ±2% accuracy at 7A with the LM3813MX-7.0?

To achieve ±2% accuracy at ±7A, TI specifies ≥100 mm² of 2-oz copper pour thermally connected to both Pin 1 (SENSE+, GND) and Pin 2 (SENSE−), with minimal trace length between them. This minimizes thermal gradients across the internal sense resistor. Avoid narrow traces or thermal relief spokes; use solid copper polygons tied directly to the pins. The D0008A package's exposed pad should also be soldered to a large ground plane for junction temperature control.

Can the LM3813MX-7.0 operate from a 3.3 V supply, and what are the implications for PWM output levels?

Yes, the LM3813MX-7.0 operates from 2.0 V to 5.25 V, including standard 3.3 V rails. At 3.3 V supply, the PWM output high level is guaranteed ≥3.1 V (VDD − 0.2 V), and low level ≤0.2 V with 1 mA sink - fully compatible with 3.3 V CMOS inputs. Quiescent current remains 100 µA typical in active mode and 2.5 µA in shutdown, ensuring predictable power budgeting in mixed-voltage systems.

Does the LM3813MX-7.0 require external filtering components, and if so, what are their values and functions?

Yes, the LM3813MX-7.0 requires two external capacitors: a 1 µF ceramic capacitor between Pin 8 (VDD) and Pin 7 (GND) for supply bypassing, and a 0.1 µF ceramic capacitor between Pins 3 (FLTR+) and 4 (FLTR−) to implement the anti-aliasing filter for the delta-sigma modulator. These values are specified in the Electrical Characteristics table and are essential to meet the 50 ms sampling interval and noise performance (20 mA rms) stated in the datasheet.