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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:
- MAX821 4-PIN MICROPROCESSOR VOLT
- Quantity:
- Payment:
- Shipping:
Inventory:2,847
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Product details
Overview
MAX821UUS+ from Maxim Integrated is an active-low microprocessor supervisory IC in SOT-143 package, monitoring +2.78V supply voltage with ±1.5% threshold accuracy over -40°C to +125°C, 2.5µA quiescent current, and pin-selectable reset timeout (1ms max / 20ms min / 100ms min) for reliable power-up sequencing in battery-powered µP systems.
For engineers reviewing the MAX821UUS+ datasheet, MAX821UUS+ pinout, MAX821UUS+ application, or MAX821UUS+ equivalent, this page delivers verified electrical parameters, thermal performance data, reset timing behavior under VCC transients, guaranteed RESET validity down to VCC = 1V, and real-world interfacing guidance for bidirectional µP reset pins.
Technical Context
The MAX821UUS+ implements a precision bandgap-based voltage comparator with hysteresis-free threshold detection and an internal monostable timer triggered on VCC crossing the reset threshold. Its SRT input directly selects one of three discrete timeout modes without external components.
Reset assertion is guaranteed for VCC falling below 2.78V (±1.5%), and the active-low RESET output remains valid-sinking ≥1.2mA at VTH(MIN)-down to VCC = 1V. The device rejects fast VCC transients ≤12µs at 100mV overdrive, per Figure 1 in the datasheet.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Reset Threshold | 2.78V ±1.5% - precisely matches 2.8V nominal supply rails; ensures reset assertion before downstream logic brownout. |
| Supply Current | 2.5µA typical - enables multi-year operation in coin-cell–powered portable instruments without compromising supervision integrity. |
| Operating Temp | -40°C to +125°C - supports industrial and automotive under-hood applications without derating or external thermal compensation. |
| Reset Timeout | Pin-selectable: 1ms (max), 20ms (min), or 100ms (min) - eliminates need for RC timing networks and associated layout sensitivity. |
| VCC Validity | RESET guaranteed low for VCC ≥1V - maintains deterministic reset state during deep brownout, critical for safe µP shutdown sequencing. |
| Transient Immunity | Rejects ≤12µs negative VCC glitches at 100mV overdrive - prevents spurious resets in noisy power environments like motor-driven handheld scanners. |
| Package | SOT-143 (4-pin) - 1.3mm × 1.3mm footprint with 0.95mm height; compatible with high-density PCB assembly and reflow profiles. |
Pinout & Package
SOT-143 package: 4-pin surface-mount, lead-free (RoHS-compliant), moisture-sensitive level 1, JEDEC standard outline drawing 21-0052.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 GND | Ground reference | Low-impedance return path for internal comparator and output stage; must be connected directly to system ground plane. |
| 2 RESET | Active-low reset output | Open-drain NMOS output sinking ≥1.2mA at VTH(MIN); requires external pull-up for logic-high when inactive. |
| 3 SRT | Set Reset Timeout input | Three-state control: GND = 1ms (max), VCC = 20ms (min), open = 100ms (min); capacitive loading <200pF required for 100ms mode. |
| 4 VCC | Supply voltage input | Monitored power rail input; operates from 1.0V to 5.5V; internal regulation enables stable threshold across full VCC range. |
Key Features
| Feature | Design Value |
|---|---|
| Pin-selectable reset timeout | Eliminates external RC timing components and reduces BOM count while supporting fast-boot (1ms) and robust-power-up (100ms) system requirements. |
| Guaranteed RESET down to VCC = 1V | Ensures deterministic reset state during deep undervoltage conditions, preventing µP latch-up or undefined execution in battery-depleted states. |
| 2.5µA supply current | Enables continuous supervision in always-on portable devices (e.g., barcode scanners) without measurable impact on battery life. |
| 30ppm/°C reset threshold tempco | Maintains tight threshold stability across industrial temperature range, avoiding false resets due to thermal drift in unregulated environments. |
| VCC transient immunity | Rejects short-duration supply noise (≤12µs at 100mV overdrive), reducing need for additional bulk capacitance or ferrite filtering on VCC rail. |
Applications
| Barcode Scanners | Portable Medical Instruments |
|---|---|
|
Use Scenario: Handheld scanner powered by single Li-ion cell with dynamic load switching causing VCC sag during laser activation. IC Role / Device Role / Timing Role: Supervisory IC asserting active-low RESET during sub-2.78V brownout events and holding reset for 20ms after recovery to ensure clean µP restart. Use Value: Prevents corrupted scan data and firmware lockup caused by partial code execution during unstable power transitions. |
Use Scenario: Battery-operated glucose meter requiring guaranteed reset during cold-start from depleted 2.8V coin cell. IC Role / Device Role / Timing Role: Voltage monitor asserting RESET until VCC exceeds 2.78V and sustaining reset for 100ms to allow analog front-end stabilization. Use Value: Eliminates need for manual power-cycle; guarantees measurement accuracy by enforcing full power-rail settling before ADC initialization. |
| Industrial PLC I/O Modules | Automotive Body Control Units |
|
Use Scenario: DIN-rail mounted controller exposed to wide ambient (-40°C to +85°C) with 5V rail subject to load-dump transients. IC Role / Device Role / Timing Role: Reset supervisor validating 5V supply integrity and rejecting ≤12µs VCC glitches induced by relay switching noise. Use Value: Reduces field failures from spurious resets, enabling compliance with IEC 61000-4-4 EFT immunity requirements without added filtering. |
Use Scenario: Under-dash BCM powered from vehicle battery with cranking-induced dips below 6V and cold-cranking down to 3.2V. IC Role / Device Role / Timing Role: Monitoring 3.3V LDO output with 2.78V threshold to assert RESET during cranking events and hold for 1ms to synchronize with µP wake-up latency. Use Value: Ensures deterministic boot sequence after engine start, eliminating communication loss with CAN gateway during voltage recovery. |
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 threshold (2.78V), timing, and package; same SRT pin behavior. | Required where host µP accepts only active-high reset signals or uses internal pull-down on reset pin. | Select MAX822UUS+ only when system-level reset polarity mandates high-asserted signaling. |
| TPS3808G12DBVR | Fixed 1.2V reset threshold; 350ms factory-programmed timeout; 1.8µA supply current; SOT-23-5 package. | Not pin-compatible; requires PCB redesign; suited for ultra-low-power 1.2V systems where 2.78V threshold is irrelevant. | Choose TPS3808G12DBVR only if system operates at 1.2V and long timeout is acceptable; not a functional substitute for MAX821UUS+. |
Compared with MAX822UUS+, the MAX821UUS+ provides inverted reset polarity essential for legacy µPs with active-low reset inputs, while both share identical threshold accuracy, temperature range, and timeout flexibility. Against TPS3808G12DBVR, MAX821UUS+ offers precise 2.78V monitoring and user-selectable timing-critical for 3V-system reliability-but in a smaller 4-pin footprint.
Availability
MAX821UUS+ is available at Aetrix Electronics and suitable for portable medical instruments, barcode scanners, industrial PLC I/O modules, and automotive body control units 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, mixed-signal, and power-management ICs for demanding industrial, automotive, and computing applications.
The MAX821/MAX822 family delivers cost-effective, single-function µP supervision with pin-selectable timing-targeting space-constrained, battery-sensitive systems where reliability under voltage stress is non-negotiable.
FAQ
What is the exact reset threshold voltage of the MAX821UUS+ and how tightly is it specified?
The MAX821UUS+ has a nominal reset threshold of 2.78V, specified with ±1.5% accuracy over the full operating temperature range (-40°C to +125°C). This value is confirmed in the Electrical Characteristics table under "VTH Reset Threshold" for the MAX82_U variant, and applies specifically to the MAX821UUS+ part number-not inferred from other MAX821 variants. The threshold remains stable with a tempco of 30ppm/°C.
Does the MAX821UUS+ support operation down to 1V supply, and what happens to the RESET output below that?
Yes, the MAX821UUS+ guarantees RESET remains a valid logic low for VCC ≥1V. When VCC falls below 1V, the RESET output stops sinking current and becomes high-impedance (open-circuit), as documented in the "Ensuring a Valid RESET Output Down to VCC = 0V" section. For applications requiring asserted RESET down to 0V, a 100kΩ pull-down resistor on the RESET pin is recommended.
How does the SRT pin select the reset timeout delay on the MAX821UUS+?
The SRT pin on the MAX821UUS+ selects timeout via three physical states: connect to GND for 1ms (maximum), connect to VCC for 20ms (minimum), or leave unconnected for 100ms (minimum). Capacitive loading on SRT must remain below 200pF when left open to avoid unintended timeout selection, per the "Setting the Reset Timeout Delay" section.
Can the MAX821UUS+ reject fast voltage transients on the VCC line, and what is its immunity specification?
Yes, the MAX821UUS+ rejects fast negative-going VCC transients. Per Figure 1 ("Maximum Transient Duration Without Causing a Reset Pulse"), it typically ignores glitches ≤12µs wide when the transient magnitude is 100mV below the reset threshold. This immunity is inherent to the comparator design and requires no external components.
Is the MAX821UUS+ pin-compatible with other MAX821 variants, and what does the 'U' suffix indicate?
Yes, all MAX821 variants-including MAX821UUS+-share identical SOT-143 pinout and electrical behavior except for reset threshold voltage. The 'U' suffix denotes the 2.78V threshold option, as shown in the Ordering Information table where MAX821UUS+ maps to NOMINAL VTH = 2.78V and TOP MARK = BL_ _. RoHS compliance (+) and tape-and-reel packaging (T) are encoded separately in the suffix.
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:
- -
- Type:
- Power Supply Monitor
- Number of Voltages Monitored:
- 1
- Voltage - Threshold:
- 2.78V
- Output:
- -
- Reset:
- Active Low
- Reset Timeout:
- 100ms Minimum
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- SOT-23-4
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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