NXP Semiconductors MMA6851BKW

Overview

MMA6851BKW from NXP Semiconductors (formerly Freescale) is a single-axis, ±25g, SPI-output inertial sensor designed for automotive airbag deployment systems. It features 10-bit digital output, programmable arming functions, 12 selectable low-pass filter options (50 Hz to 1000 Hz), and AEC-Q100 Grade 2 qualification for under-hood operation.

For engineers reviewing the MMA6851BKW datasheet, MMA6851BKW pinout, MMA6851BKW application, or MMA6851BKW equivalent, this page delivers verified technical context, exact pin roles, real-world automotive use cases, and validated alternative part comparisons - all grounded in the official Rev 4 (Dec 2011) technical data sheet.

Technical Context

The MMA6851BKW integrates an over-damped lateral MEMS g-cell with a ΣΔ ADC, SINC-based digital filtering, and configurable IIR low-pass filters. Its internal 8 MHz oscillator feeds a programmable clock divider to support 12 discrete LPF cutoff frequencies across two timing groups (ts = 8 μs and 16 μs).

It implements dual-regulator architecture: VREG (2.5 V ±0.08 V) powers digital logic, while VREGA (2.5 V ±0.08 V) supplies analog circuitry. The ARM/PCM pin supports three arming modes - moving average, count, or unfiltered - with open-drain configuration and user-selectable polarity via DEVCFG register bits A_CFG[2:0].

Key Specifications

Pinout & Package

Pb-free 16-pin QFN package, 6 mm × 6 mm, exposed thermal pad (Case 2086-01). Pin 17 (PAD) and corner pads internally connected to VSS.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar single-axis inertial sensing applications.

Compared with MMA6853BKW and ADXL206, the MMA6851BKW offers the narrowest full-scale range and highest LSB/g resolution among Freescale's MMA685x family, making it optimal for precision low-g crash event discrimination - whereas MMA6853BKW trades resolution for headroom, and ADXL206 introduces external signal conditioning complexity and certification gaps.

Availability

MMA6851BKW is available at Aetrix Electronics and suitable for automotive airbag control units, rollover detection modules, and pre-crash sensing systems requiring stable component supply, AEC-Q100-compliant traceability, and long-term production continuity.

Supply support for MMA6851BKW 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

NXP Semiconductors is a global semiconductor leader focused on secure connectivity solutions for automotive, industrial, and IoT applications.

The MMA6851BKW belongs to NXP's automotive-grade inertial sensor product line, engineered specifically for safety-critical airbag deployment systems requiring high reliability, deterministic timing, and robustness under extreme mechanical stress.

FAQ

What is the full-scale range and digital sensitivity of the MMA6851BKW?

The MMA6851BKW has a ±25g full-scale range and a nominal digital sensitivity of 20.479 LSB/g for 10-bit unsigned output. This value is factory-trimmed and specified at 100 Hz with 1000 Hz low-pass filter enabled. Sensitivity error is ±4% over 25°C and ±5% across −40°C to +105°C operating temperature. The MMA6851BKW uses this precise scaling to deliver repeatable acceleration quantization for airbag decision algorithms.

Does the MMA6851BKW support both signed and unsigned SPI data formats?

Yes, the MMA6851BKW supports both signed and unsigned 10-bit SPI output formats. The SD bit in the DEVCFG register controls this: when SD = 1, output is unsigned with zero-g at 512 LSB; when SD = 0, output is signed with zero-g at 0 LSB. This flexibility allows seamless integration with microcontrollers expecting either format without external translation logic. The MMA6851BKW's register-based configuration ensures runtime reconfiguration capability.

How is the ARM/PCM pin configured for arming output in the MMA6851BKW?

The ARM/PCM pin on the MMA6851BKW is configured via A_CFG[2:0] bits in the DEVCFG register. Valid modes include moving average (active high/low), count mode, and unfiltered mode - all implemented as open-drain outputs with programmable pullup/pulldown current. The MMA6851BKW's arming logic operates independently of the SPI interface, enabling hardware-triggered airbag deployment with sub-microsecond assertion delay (as low as 1.05 μs in unfiltered mode).

What low-pass filter options does the MMA6851BKW offer, and how are they selected?

The MMA6851BKW provides 12 low-pass filter options: six at ts = 8 μs (100–1000 Hz) and six at ts = 16 μs (50–500 Hz), selectable via LPF[3:0] bits in the DEVCFG_X register. Each option uses either 4-pole or 3-pole topology. The MMA6851BKW's filter selection directly impacts noise rejection and group delay - e.g., 400 Hz 4-pole LPF yields 0.5 LSB RMS noise and 36.5 μs latency - enabling optimization for specific crash pulse profiles.

Is the MMA6851BKW qualified for automotive applications, and what standards does it meet?

Yes, the MMA6851BKW is qualified per AEC-Q100 Revision G (May 2007) for Grade 2 operation (−40°C to +105°C ambient). It also meets stringent mechanical robustness requirements: ±1500 g powered shock (0.5 ms), ±2000 g unpowered shock, and 1.2 m drop shock onto concrete. These qualifications confirm the MMA6851BKW's suitability for safety-critical automotive airbag systems where failure is not an option.