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Analog Devices Inc./Maxim Integrated MAX821TUS
- Part No.:
- MAX821TUS
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Supervisors
- Package:
- TO-253-4, TO-253AA
- Datasheet:
-
MAX821TUS.pdf
- Description:
- IC SUPERVISOR MPU VOLT MONITOR
- Quantity:
- Payment:
- Shipping:
Inventory:2,609
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Product details
Overview
MAX821TUS from Maxim Integrated is an active-low microprocessor supervisory IC in SOT-143 package, designed to monitor +3V to +5V power supplies and assert a reset signal when VCC falls below a factory-trimmed 3.08V threshold. It provides pin-selectable reset timeout delays (1ms max, 20ms min, or 100ms min) and guarantees valid RESET output down to VCC = 1V. Used in portable battery-powered equipment and critical µP power monitoring.
For engineers reviewing the MAX821TUS datasheet, MAX821TUS pinout, MAX821TUS application, or MAX821TUS equivalent, this page delivers verified specifications, thermal performance across –40°C to +125°C, SRT input configuration logic, reset comparator transient immunity, and design-meaningful alternatives for voltage-monitoring system integration.
Technical Context
The MAX821TUS implements a precision bandgap-based reset comparator with 30ppm/°C tempco, enabling stable threshold accuracy over temperature. Its internal timer initiates only after VCC rises above the 3.08V threshold and remains active during brownout recovery - resetting on each VCC dip below threshold.
SRT pin state directly controls timeout duration: grounded for 1ms (max), tied to VCC for 20ms (min), or floating (≤200pF loading) for 100ms (min). The device draws just 2.5µA typical supply current and tolerates fast transients (e.g., ≤12µs at 100mV overdrive) without false triggering.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Reset Threshold | 3.08V nominal; ensures reliable reset assertion before downstream logic fails under 3.3V supply brownout. |
| Supply Current | 2.5µA typical; enables multi-year operation in coin-cell–powered portable instruments. |
| Operating Temp | –40°C to +125°C; supports industrial and automotive under-hood applications without derating. |
| Reset Timeout | PIN-selectable: 1ms (max), 20ms (min), or 100ms (min); eliminates need for external RC timing networks. |
| VCC Range | 1.0V to 5.5V; allows valid RESET assertion down to 1V while maintaining compatibility with 3.3V/5V systems. |
| Threshold Tempco | 30ppm/°C; limits threshold drift to ±0.3% over full temperature range, ensuring consistent trip point. |
| Output Type | Active-low open-drain RESET; sinks 1.2mA at VTH(MIN), compatible with standard CMOS µP reset inputs. |
Pinout & Package
SOT-143 (4-pin, 1.3mm × 2.1mm) surface-mount package with exposed pad option; leaded variant per ordering suffix "-T".
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 GND | Ground reference | Return path for internal comparator and output stage; must be low-impedance for noise immunity. |
| 2 RESET | Active-low reset output | Open-drain output asserted low during VCC undervoltage or timeout; requires external pull-up for µP interface. |
| 3 SRT | Set Reset Timeout input | Three-state control: GND → 1ms, VCC → 20ms, open → 100ms; capacitive loading <200pF required for 100ms mode. |
| 4 VCC | Supply voltage input | Monitored rail input; powers internal circuitry and defines reset threshold reference; rated –0.3V to 6.0V absolute max. |
Key Features
| Feature | Design Value |
|---|---|
| Pin-selectable reset timeout | Eliminates external timing components and PCB layout changes when adapting reset delay across product variants. |
| Guaranteed RESET validity to VCC = 1V | Ensures deterministic µP reset state even during deep brownout, preventing undefined boot behavior in battery-depleted systems. |
| 2.5µA supply current | Reduces quiescent power by >90% vs. discrete resistor-zener solutions, extending runtime in always-on sensors. |
| 30ppm/°C reset threshold tempco | Maintains ±0.3% threshold stability across –40°C to +125°C, avoiding recalibration in wide-temperature deployments. |
| Transient-immune comparator | Rejects VCC glitches ≤12µs at 100mV overdrive, preventing spurious resets in noisy switching-power-supply environments. |
Applications
| Bar-Code Scanners | Portable Medical Devices |
|---|---|
|
Use Scenario: Handheld scanner powered by single Li-ion cell with dynamic load-induced VCC sag during laser activation. IC Role / Device Role / Timing Role: Voltage monitor asserting active-low RESET to halt processor until stable 3.3V rail is restored post-sag. Use Value: Prevents firmware crash during intermittent power dips; 1ms timeout enables rapid resumption of scanning after brief brownouts. |
Use Scenario: Battery-operated glucose meter requiring guaranteed boot integrity after cold storage (-20°C) and partial discharge. IC Role / Device Role / Timing Role: Supervisory IC validating VCC ≥3.08V before releasing µP from reset, with 100ms timeout ensuring full LDO stabilization. Use Value: Eliminates risk of corrupted EEPROM writes or sensor initialization failure due to premature release from reset. |
| Industrial PLC I/O Modules | Smart Energy Meters |
|
Use Scenario: DIN-rail mounted controller exposed to 85°C ambient and conducted EMI on 24V DC input converted to 3.3V. IC Role / Device Role / Timing Role: High-temp-stable voltage supervisor monitoring local 3.3V rail, asserting RESET during input ripple-induced sags. Use Value: 125°C rating and 30ppm/°C tempco prevent false resets in thermally stressed enclosures; SRT tied to VCC selects 20ms delay for robust startup. |
Use Scenario: Revenue-grade meter with tamper-detection circuitry that must retain secure state during AC mains dropout. IC Role / Device Role / Timing Role: Primary reset supervisor holding µP in reset during VCC decay from backup capacitor, with 100ms timeout aligning to supercap discharge profile. Use Value: Guarantees secure shutdown sequence execution before VCC drops below 1V, preserving cryptographic key integrity. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar voltage-monitoring applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX809TRD3 | Fixed 3.08V threshold, 240ms reset timeout, SOT-23-3 package, no SRT pin. | Lacks pin-selectable delay; requires PCB redesign for timeout change; smaller footprint but no flexibility. | Choose when fixed long timeout suffices and board space is constrained. |
| TPS3808G30DBVR | 3.0V threshold, 200ms timeout, adjustable via external capacitor, 6-pin SOT-23, higher ICC (8µA). | Capacitor-programmable delay adds BOM cost and layout sensitivity; wider VCC range (0.8–6V). | Prefer when fine-grained timeout tuning is needed and 5.5V max VCC is insufficient. |
Compared with MAX821TUS, MAX809TRD3 trades programmability for compactness and MAX821TUS offers lower quiescent current and guaranteed 1V operation versus TPS3808G30DBVR - making MAX821TUS optimal for battery-critical, thermally demanding, or brownout-prone designs where pin-selectable delay and ultra-low ICC are decisive.
Availability
MAX821TUS is available at Aetrix Electronics and suitable for portable medical devices, industrial PLC I/O modules, smart energy meters, and bar-code scanners requiring stable component supply across extended temperature and long-lifecycle programs.
Supply support for MAX821TUS 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 high-performance analog and mixed-signal ICs for industrial, communications, and computing markets, with emphasis on power efficiency and reliability.
The MAX821 series belongs to Maxim's µP supervisory product line, engineered specifically for deterministic power-on/power-down reset generation in resource-constrained embedded systems where precision, low ICC, and thermal robustness are essential.
FAQ
What is the exact reset threshold voltage for MAX821TUS?
The MAX821TUS has a nominal reset threshold of 3.08V, with guaranteed minimum and maximum values of 3.00V and 3.15V respectively over the full –40°C to +125°C operating temperature range. This value is factory-trimmed and specified in the Electrical Characteristics table of the MAX821/MAX822 datasheet (Rev 3, 2006). The 3.08V threshold ensures compatibility with 3.3V systems while providing sufficient margin above typical 3.0V logic low thresholds.
How does the SRT pin configure the reset timeout on MAX821TUS?
On the MAX821TUS, the SRT pin sets the reset timeout period: connecting SRT to GND selects 1ms (maximum), tying it to VCC selects 20ms (minimum), and leaving it unconnected (with <200pF capacitance) selects 100ms (minimum). This three-state configuration eliminates external timing components. The internal timer begins counting only after VCC rises above the 3.08V threshold, and any subsequent VCC dip below threshold resets the timer.
Can MAX821TUS operate reliably at 125°C ambient temperature?
Yes, the MAX821TUS is fully specified and guaranteed to operate from –40°C to +125°C ambient temperature. All key parameters-including reset threshold (±0.3% drift), supply current (2.5µA typ), and timeout accuracy-are characterized across this range. The 30ppm/°C tempco ensures minimal threshold shift, and the SOT-143 package supports thermal dissipation up to 320mW at +70°C with standard derating.
Does MAX821TUS provide a valid reset signal when VCC drops below 1V?
No - the MAX821TUS guarantees valid RESET output only down to VCC = 1V. Below 1V, the RESET output becomes high-impedance (open-circuit) and cannot actively drive low. For applications requiring asserted reset down to 0V, a 100kΩ pull-down resistor on the RESET pin is recommended, as documented in the "Ensuring a Valid RESET Output Down to VCC = 0V" section of the MAX821/MAX822 datasheet.
What is the maximum capacitive loading allowed on the SRT pin for 100ms timeout mode on MAX821TUS?
For reliable 100ms timeout operation, the SRT pin on MAX821TUS must be left unconnected with total capacitive loading less than 200pF. Exceeding this limit may cause unintended selection of faster timeout modes (e.g., 20ms or 1ms) due to slow RC charging. Layout best practice is to minimize trace length and avoid nearby signal routing or ground planes adjacent to the SRT net.
MAX821TUS 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:
- 3.08V
- 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
MAX821TUS FAQ
1.How can I place an order for MAX821TUS through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX821TUS 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 MAX821TUS reliable?
The price and inventory of MAX821TUS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX821TUS is usually 5 days.
3.What payment methods are accepted for MAX821TUS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX821TUS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX821TUS?
MAX821TUS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX821TUS 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 MAX821TUS?
For technical support, including MAX821TUS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX821TUS requirements.
6.How does Aetrix verify that MAX821TUS is sourced from the original manufacturer or authorized distributors?
All MAX821TUS 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 MAX821TUS meets industry standards.
7.What is the process for return or replacement of MAX821TUS?
All MAX821TUS units undergo pre-shipment inspection (PSI). If there is an issue with MAX821TUS, 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 MAX821TUS part is unused and in its original packaging.
Return procedure for MAX821TUS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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