Microchip Technology MIC74BQS-TR

Overview

MIC74BQS-TR from Microchip Technology is an SMBus/I²C-compatible 8-bit serial-to-parallel I/O expander with integrated fan speed control logic, operating from 2.7V to 3.6V, featuring 5V-tolerant I/O pins, 2 µA typical quiescent current, and programmable push-pull or open-drain outputs-used in PC system management and microcontroller I/O expansion.

For engineers reviewing the MIC74BQS-TR datasheet, MIC74BQS-TR pinout, MIC74BQS-TR application, or MIC74BQS-TR equivalent, key selection considerations include its QSOP-16 package, interrupt-on-change capability via /ALERT, fan mode configuration (P7–P4 as /FS2–/FS0 and /SHDN), register-based I/O direction/output type control, and support for up to eight devices per bus.

Technical Context

The MIC74BQS-TR implements a 2-wire SMBus/I²C interface with standard Read_Byte/Write_Byte protocols and Alert Response Address (ARA = 0x14) handling. It uses seven internal registers-including DEV_CFG, DIR, OUT_CFG, STATUS, INT_MASK, DATA, and FAN_SPEED-to configure I/O direction, output drive type, interrupt masking, and fan control states.

Its dual-mode operation supports general-purpose I/O expansion (P0–P7 as configurable inputs/outputs) and dedicated fan control mode where P4–P7 become /SHDN and /FS2–/FS0 outputs driven by the FAN_SPEED register, with automatic tSTART (~1 s) startup sequencing and internal state-machine timing control-eliminating host bit-banging overhead.

Key Specifications

Pinout & Package

The MIC74BQS-TR is housed in a 16-pin QSOP (Quarter-Size Outline Package) with 0.65 mm lead pitch and 1.9 mm body height - optimized for space-constrained portable and desktop PCB layouts.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I/O expansion applications.

Compared with PCA9555DWR and TCA6408APWR, the MIC74BQS-TR uniquely integrates fan control logic with automatic startup sequencing and dedicated /SHDN+/FS outputs-reducing BOM count and firmware burden in thermal management applications, while maintaining identical 8-bit I/O expandability and SMBus compatibility.

Availability

MIC74BQS-TR is available at Aetrix Electronics and suitable for PC system management, microcontroller I/O expansion, and fan control applications requiring stable component supply, long-term lifecycle support, and consistent QSOP-16 packaging.

Supply support for MIC74BQS-TR 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

Microchip Technology is a U.S.-based semiconductor company specializing in microcontrollers, analog devices, and interface ICs, with a focus on embedded control and system management solutions.

The MIC74 product line is designed specifically for SMBus-based I/O expansion and thermal subsystem control in computing and embedded platforms-emphasizing low power, interrupt efficiency, and integrated fan logic.

FAQ

What is the primary function of the MIC74BQS-TR?

The MIC74BQS-TR is an 8-bit SMBus/I²C-compatible I/O expander with integrated fan speed control logic. It provides programmable general-purpose I/O (P0–P7), interrupt-on-change capability via /ALERT, and hardware-managed fan control outputs (/SHDN, /FS2–/FS0). Its core function is to extend microcontroller or EC GPIO resources while offloading thermal management tasks - all in a single QSOP-16 package. The MIC74BQS-TR achieves this through seven internal registers that configure I/O direction, drive type, interrupt masking, and fan behavior without host firmware timing loops.

Does the MIC74BQS-TR support 5V logic levels on its I/O pins?

Yes, the MIC74BQS-TR features 5V-tolerant I/O pins (P0–P7, A0–A2, /ALERT), meaning it can safely accept input voltages up to 5.5V regardless of its 2.7V–3.6V VDD supply. This allows direct interfacing with 5V sensors, switches, or LED drivers without level-shifting circuitry. However, output high voltage is limited to VDD (max 3.6V), so external pull-ups to 5V must be used only on inputs or open-drain outputs like /ALERT and DATA - not on push-pull outputs. The MIC74BQS-TR's 5V tolerance is explicitly specified in its Absolute Maximum Ratings and Electrical Characteristics tables.

How does fan control work on the MIC74BQS-TR?

Fan control on the MIC74BQS-TR is activated by setting the FAN bit (D1) in the DEV_CFG register (address 0x00). When enabled, P4–P7 become dedicated outputs: P4 = /SHDN, P5 = /FS0, P6 = /FS1, P7 = /FS2. Their states are governed solely by the 3-bit FAN_SPEED register (address 0x06), which selects one of eight fan profiles (off + seven speeds). Crucially, the MIC74BQS-TR includes built-in timing logic: writing a non-zero value to FAN_SPEED triggers a ~1-second tSTART pulse where /FS2–/FS0 go high and /SHDN is deasserted first, ensuring reliable fan spin-up - all handled autonomously without MCU involvement. This hardware sequencing is a defining feature of the MIC74BQS-TR.

What is the purpose of the /ALERT pin on the MIC74BQS-TR?

On the MIC74BQS-TR, the /ALERT pin is an open-drain, active-low interrupt output that signals input state changes on configured I/O pins (P0–P3 in I/O mode; no interrupts in fan mode). It asserts within <4 µs of a qualifying edge (per INT_MASK and global IE bit settings) and remains active until cleared - either by the host reading the STATUS register or responding to the Alert Response Address (ARA = 0x14). This eliminates polling, reduces SMBus traffic, and enables immediate host response to events like button presses or sensor triggers. The MIC74BQS-TR's /ALERT behavior is fully compliant with SMBus specification requirements for interrupt reporting and clearing.

Can multiple MIC74BQS-TR devices share the same SMBus?

Yes, up to eight MIC74BQS-TR devices can operate on a single SMBus. Each device uses its A0, A1, and A2 pins to set the three least-significant bits of its 7-bit client address, yielding addresses from 0x20 to 0x27. These pins are sampled only once at power-on, so address configuration is static after initial power-up. This multi-drop capability allows scalable I/O expansion - for example, eight MIC74BQS-TR units provide 64 total programmable I/O lines with shared clock/data lines and a single /ALERT wire per device. The MIC74BQS-TR's address mapping and bus arbitration are fully SMBus-compliant and verified in Microchip's DS20005969A datasheet.