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Analog Devices Inc./Maxim Integrated MAX821UUS
- Part No.:
- MAX821UUS
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Supervisors
- Package:
- TO-253-4, TO-253AA
- Datasheet:
-
MAX821UUS.pdf
- Description:
- IC SUPERVISOR MPU VOLT MONITOR
- Quantity:
- Payment:
- Shipping:
Inventory:4,342
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Product details
Overview
MAX821UUS from Maxim Integrated is an active-low microprocessor supervisory IC that monitors +2.78V supply voltage and asserts a guaranteed logic-low RESET signal down to VCC = 1V. It provides pin-selectable power-on reset timeout delays (1ms max, 20ms min, or 100ms min) and operates across –40°C to +125°C. Used in portable battery-powered equipment for reliable µP power-up sequencing.
For engineers reviewing the MAX821UUS datasheet, MAX821UUS pinout, MAX821UUS application, or MAX821UUS equivalent, key selection criteria include its 2.78V reset threshold, SOT143-4 package, 2.5µA supply current, and guaranteed RESET validity at VCC ≥ 1V - critical for low-voltage brownout detection in handheld instruments and embedded controllers.
Technical Context
The MAX821UUS implements a precision bandgap-based voltage comparator with ±1.5% reset threshold accuracy over temperature and a dedicated internal timer for reset timeout generation. Its SRT input directly selects one of three discrete delay modes without external components.
Reset assertion is triggered when VCC falls below 2.78V (nominal), and the output remains asserted for the selected timeout after VCC rises above threshold. The comparator ignores transients ≤12µs at 100mV overdrive, ensuring immunity to short supply glitches.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Reset Threshold | 2.78V nominal; ensures reliable reset assertion before downstream logic fails under brownout |
| Supply Current | 2.5µA typical; enables multi-year operation in coin-cell–powered devices |
| Operating Temp | –40°C to +125°C; supports industrial and automotive under-hood applications |
| Reset Timeout Options | 1ms (max), 20ms (min), or 100ms (min); selected via SRT pin connection state |
| VCC Validity Range | RESET guaranteed low for VCC ≥ 1V; allows functional reset signaling during deep brownout |
| Transient Immunity | Rejects VCC glitches ≤12µs wide at 100mV overdrive; prevents false resets in noisy environments |
| Package | SOT143-4; 1.3mm × 2.1mm footprint ideal for space-constrained portable PCBs |
Pinout & Package
SOT143-4 surface-mount package with 1.3mm × 2.1mm body, 0.95mm height, and 0.95mm lead pitch. RoHS-compliant lead-free variant available (MAX821UUS+T).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 GND | Ground reference | Return path for internal comparator and output driver; must be low-impedance |
| 2 RESET | Active-low reset output | Open-drain output pulled low during reset; requires external pull-up for logic-high state |
| 3 SRT | Set Reset Timeout input | Three-state control: GND = 1ms, VCC = 20ms, open = 100ms; <200pF loading required for 100ms mode |
| 4 VCC | Supply voltage input | Monitored rail; powers internal circuitry and defines reset threshold reference |
Key Features
| Feature | Design Value |
|---|---|
| No external components required | Integrates voltage reference, comparator, timer, and output driver - eliminates BOM cost and layout area |
| Guaranteed RESET down to VCC = 1V | Ensures deterministic reset behavior even during severe brownout, preventing undefined µP states |
| Pin-selectable reset timeout | Hardware-configurable delay avoids firmware dependency and enables rapid design iteration |
| Power-supply transient immunity | Rejects sub-12µs supply noise without filtering capacitors - reduces system-level EMI susceptibility |
| Wide temperature range support | Validated operation from –40°C to +125°C enables use in uncontrolled environments like industrial sensors |
Applications
| Bar-Code Scanners | Portable Medical Instruments |
|---|---|
Use Scenario: Handheld scanners powered by single-cell Li-ion batteries experiencing voltage sag during motor activation. IC Role / Device Role / Timing Role: Monitors VCC and asserts RESET if voltage drops below 2.78V, holding it for 20ms after recovery to ensure clean µP restart. Use Value: Prevents corrupted scan data and firmware lockup caused by brownout-induced instruction errors. |
Use Scenario: Battery-operated glucose meters requiring guaranteed startup integrity after cold storage (-20°C). IC Role / Device Role / Timing Role: Provides 100ms reset timeout at low temperature to accommodate slow power-rail stabilization in LCD and sensor subsystems. Use Value: Eliminates manual reset requirement and ensures first-power reliability across full medical operating range. |
| Industrial PLC I/O Modules | Smart Energy Meters |
Use Scenario: DIN-rail mounted modules exposed to 48V DC supply ripple and load-dump transients. IC Role / Device Role / Timing Role: Detects sustained undervoltage on 3.3V logic rail and initiates controlled reboot with 1ms timeout for fast recovery. Use Value: Maintains communication link continuity by avoiding extended watchdog timeouts during brief supply disturbances. |
Use Scenario: Meters with supercapacitor backup that must retain RTC and metering registers during AC mains failure. IC Role / Device Role / Timing Role: Monitors 3.3V backup rail and triggers immediate RESET at 2.78V to initiate safe shutdown sequence before capacitor depletion. Use Value: Guarantees nonvolatile memory write completion and prevents EEPROM corruption during power loss. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar microprocessor supervisory applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX822UUS | Active-high RESET output; identical reset threshold (2.78V), timing, and package | Required where host µP accepts only active-high reset assertion | Select MAX822UUS when interfacing with processors lacking internal pull-down or requiring high-true reset logic |
| TPS3808G12DBVR | Fixed 1.2V reset threshold; 350ms default timeout (non-pin-selectable); higher 8µA quiescent current | Designed for ultra-low-voltage systems (e.g., 1.8V logic rails); lacks brownout detection margin for 2.78V operation | Choose TPS3808G12DBVR only for 1.2V supply monitoring; not functionally substitutable for 2.78V threshold requirement |
Compared with MAX822UUS, the MAX821UUS provides identical supervision accuracy and timing but delivers active-low reset compatible with legacy µPs. Against TPS3808G12DBVR, it offers precise 2.78V threshold matching and lower power, making it superior for 3V-system brownout protection where threshold alignment and battery life are critical.
Availability
MAX821UUS is available at Aetrix Electronics and suitable for portable medical instruments, industrial PLC I/O modules, and smart energy meters requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for MAX821UUS 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
Maxim Integrated (now part of Analog Devices) designs precision analog and mixed-signal ICs for power, sensing, and interface applications, with emphasis on high-reliability industrial and automotive solutions.
The MAX821/MAX822 product line delivers compact, low-power supervisory circuits optimized for robust µP reset generation in battery-powered and harsh-environment systems.
FAQ
What is the exact reset threshold voltage for MAX821UUS?
The MAX821UUS has a nominal reset threshold of 2.78V, with guaranteed minimum/maximum values of 2.70V and 2.85V over –40°C to +125°C. This value is laser-trimmed during production and specified in the Electrical Characteristics table of the MAX821/MAX822 datasheet (Rev 3, 2006). The 2.78V threshold ensures compatibility with 3V logic systems while providing sufficient margin above typical 2.7V brownout limits.
How does the SRT pin configure the reset timeout on MAX821UUS?
On the MAX821UUS, the SRT pin selects reset timeout by connection state: tying SRT to GND yields 1ms (maximum), connecting to VCC yields 20ms (minimum), and leaving it unconnected yields 100ms (minimum). Capacitive loading on SRT must remain below 200pF for reliable 100ms operation. This hardware-based selection eliminates firmware dependencies and ensures deterministic timing at power-up.
Is MAX821UUS compatible with 1.8V or 2.5V supply rails?
No - the MAX821UUS is specifically trimmed for 2.78V reset threshold and characterized for operation with VCC between 1.0V and 5.5V, but its threshold is fixed and not adjustable. For 1.8V or 2.5V rails, select variants like MAX821TUS (3.08V) or MAX821SUS (2.93V). Using MAX821UUS on lower rails would assert reset prematurely; it is designed exclusively for systems where 2.78V represents the valid operational floor.
Does MAX821UUS require an external pull-up resistor on the RESET pin?
Yes - the MAX821UUS features an open-drain RESET output and requires an external pull-up resistor to VCC (typically 10kΩ–100kΩ) to establish a defined logic-high state when not asserting reset. Without it, the RESET line floats during inactive periods, risking indeterminate µP behavior. This is explicitly documented in the "Ensuring a Valid RESET Output Down to VCC = 0V" section of the datasheet.
What is the maximum VCC voltage rating for MAX821UUS?
The absolute maximum VCC rating for MAX821UUS is 6.0V, per the Absolute Maximum Ratings table. Continuous operation is specified up to 5.5V across the full temperature range. Exceeding 6.0V risks permanent damage; operation between 5.5V and 6.0V is limited to short-duration transients only and is not recommended for sustained use. Always maintain VCC within 1.0V to 5.5V for reliable functionality.
MAX821UUS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Series:
- -
- Package/Case:
- TO-253-4, TO-253AA
- Packaging:
- Bulk
- Product Status:
- Active
- Programmable:
- Not Verified
- Type:
- Simple Reset/Power-On Reset
- Number of Voltages Monitored:
- 1
- Voltage - Threshold:
- 2.78V
- Output:
- Push-Pull, Totem Pole
- Reset:
- Active Low
- Reset Timeout:
- Adjustable/Selectable
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SOT-143-4
MAX821UUS FAQ
1.How can I place an order for MAX821UUS through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX821UUS on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for MAX821UUS reliable?
The price and inventory of MAX821UUS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX821UUS is usually 5 days.
3.What payment methods are accepted for MAX821UUS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX821UUS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX821UUS?
MAX821UUS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX821UUS order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for MAX821UUS?
For technical support, including MAX821UUS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX821UUS requirements.
6.How does Aetrix verify that MAX821UUS is sourced from the original manufacturer or authorized distributors?
All MAX821UUS products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MAX821UUS meets industry standards.
7.What is the process for return or replacement of MAX821UUS?
All MAX821UUS units undergo pre-shipment inspection (PSI). If there is an issue with MAX821UUS, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The MAX821UUS part is unused and in its original packaging.
Return procedure for MAX821UUS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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