ADM1021AARQZ-REEL

Overview

The ADM1021AARQZ-REEL is a low-cost microprocessor system temperature monitor manufactured by onsemi. It functions as a two-channel digital thermometer and undertemperature/overtemperature alarm designed for thermal monitoring in personal computers and other systems. The device features an on-chip temperature sensor and supports remote sensing via a diode-connected PNP transistor, eliminating the need for calibration. It communicates through a two-wire SMBus serial interface compatible with SMBus standards, allowing programmable overtemperature and undertemperature limits. The component operates within a supply voltage range of 3 V to 5.5 V and includes an ALERT output for interrupt signaling.

Feature Summary

• Two-channel digital temperature measurement capability utilizing both on-chip and remote sensors
• SMBus-compatible two-wire serial interface for configuration and data retrieval
• Programmable overtemperature and undertemperature limit thresholds
• Open-drain ALERT output for interrupt or system management bus alert signaling

Applications

• Desktop computers
• Notebook computers
• Smart batteries
• Industrial controllers
• Telecom equipment

Procurement Notes

Verify that the ordering suffix REEL7 corresponds to tape-and-reel packaging when sourcing from distributors. Confirm RoHS compliance status, as datasheets may indicate non-compliance for specific manufacturing batches or older revisions. Ensure the manufacturer is identified as onsemi, noting the historical transition from Analog Devices. Validate pinout compatibility if replacing legacy ADM1021 units, as register defaults and current sourcing levels differ between the original and A variants.

Selection Notes

Select this component for applications requiring calibrated-free temperature monitoring of microprocessors using integrated or discrete NPN/PNP transistors. It is suitable for systems needing dual-zone thermal management with programmable alerts. Consider the SMBus interface requirements and address pin configurations (ADD0, ADD1) for multi-device bus setups. Evaluate power consumption needs against the available conversion rates, as lower rates significantly reduce operating current. Ensure the operating temperature range aligns with the specified -55°C to +125°C environment.

Part Context

This part belongs to the ADM1021 family of temperature monitors. The ADM1021A variant offers improvements over the original ADM1021, including higher remote sensor source current for better noise immunity and a different temperature measurement range starting from 0°C. It maintains pin-for-pin compatibility but differs in register defaults and internal current biasing. The device is widely used in PC thermal management solutions where cost-effective, accurate monitoring is required without external calibration components.

Replacement Considerations

The ADM1021 is a pin-compatible predecessor but has distinct differences in register defaults, measurement range, and sensor current. Replacement requires verifying software compatibility with the ADM1021A's undefined address pointer default and different revision ID. Ensure the application does not require negative temperature measurement below 0°C, which the ADM1021A cannot support.

FAQ

How does the ADM1021A handle remote sensor open-circuit detection?

The device sets a specific flag in the Status Register (Bit 2, OPEN) when the remote temperature sensor is detected as open-circuit. This flag contributes to triggering the ALERT output if enabled.

What is the purpose of the STBY pin?

The STBY pin allows the user to manually place the device into standby mode. When pulled low, it disables the ADC conversion, reducing power consumption while retaining the last measured temperature values in the registers.

Can multiple ADM1021A devices be used on the same SMBus?

Yes, up to nine devices can be connected to the same SMBus. This is achieved by configuring the three-state logic inputs ADD0 and ADD1 to different combinations of ground, VDD, or floating states to assign unique device addresses.