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Analog Devices Inc./Maxim Integrated MAX821LUS
- Part No.:
- MAX821LUS
- Manufacturer:
- Analog Devices Inc./Maxim Integrated
- Category:
- Supervisors
- Package:
- TO-253-4, TO-253AA
- Datasheet:
-
MAX821LUS.pdf
- Description:
- IC SUPERVISOR MPU VOLT MONITOR
- Quantity:
- Payment:
- Shipping:
Inventory:8,003
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Product details
Overview
MAX821LUS from Maxim Integrated is an active-low microprocessor supervisory IC that monitors +4.38V supply voltage and asserts a reset signal when VCC falls below threshold, maintaining reset for a pin-selectable timeout (1ms max, 20ms min, or 100ms min) after recovery - used in portable equipment, bar-code scanners, and critical µP power monitoring.
For engineers reviewing the MAX821LUS datasheet, MAX821LUS pinout, MAX821LUS application, or MAX821LUS equivalent, this page delivers verified specifications, SOT143 package details, reset timing behavior across temperature, guaranteed RESET validity down to VCC = 1V, and real-world interface guidance for bidirectional µP reset pins.
Technical Context
The MAX821LUS implements a precision voltage comparator with 30ppm/°C tempco and hysteresis-immune brownout detection, paired with a digital timeout timer controlled solely by the SRT pin state (GND/VCC/unconnected). Its internal architecture guarantees monotonic reset assertion during VCC ramp-up and immediate reassertion on any VCC dip below threshold.
Reset output is actively driven low with 3.2mA sink capability at VTH(MIN), remains valid down to VCC = 1V, and exhibits transient immunity against negative-going VCC glitches ≤12µs at 100mV overdrive - confirmed across -40°C to +125°C operation without external components.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Reset Threshold | 4.38V nominal (L-grade), ±1.5% accuracy over -40°C to +125°C - ensures reliable assertion before system ICs drop out of spec. |
| Supply Current | 2.5µA typical at +25°C - enables multi-year battery life in portable equipment without compromising supervision integrity. |
| Reset Timeout Options | 1ms (max), 20ms (min), or 100ms (min) - selected via SRT pin connection, eliminating need for external RC timing networks. |
| Operating Temp Range | -40°C to +125°C - qualified for automotive under-hood, industrial control, and extended-temperature embedded applications. |
| VCC Validity Range | RESET output guaranteed functional down to VCC = 1V - supports safe reset hold during deep brownout or backup power switchover. |
| Output Drive Strength | 3.2mA sink at VTH(MIN) - directly drives standard CMOS reset inputs without pull-up resistor or buffer stage. |
| Transient Immunity | Rejects VCC glitches ≤12µs wide at 100mV below threshold - prevents spurious resets in noisy power environments. |
Pinout & Package
SOT143-4 surface-mount package (4-pin, 1.3mm × 2.1mm footprint, 0.95mm height), leaded variant per ordering suffix "-T", RoHS-compliant option available as MAX821LUS+T.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 GND | Ground reference | Return path for internal comparator and output driver; must be low-impedance connection to system ground plane. |
| 2 RESET | Active-low reset output | Open-drain compatible output asserted low during VCC fault and for full timeout period; sinks up to 3.2mA. |
| 3 SRT | Set Reset Timeout input | Digital control pin: GND = 1ms max delay, VCC = 20ms min delay, unconnected = 100ms min delay; <200pF loading required for 100ms mode. |
| 4 VCC | Supply voltage input | Monitored power rail input (4.38V nominal); accepts 1.0V to 5.5V range; internal regulator enables operation down to 1V. |
Key Features
| Feature | Design Value |
|---|---|
| Pin-selectable reset timeout | Three deterministic delays (1ms/20ms/100ms) set by SRT pin state - eliminates timing capacitor variability and board space. |
| +4.38V precision threshold | Guaranteed ±1.5% tolerance over full temperature range - matches 5V system rails with margin for regulation drift and load transients. |
| Ultra-low quiescent current | 2.5µA typical - reduces standby power in battery-backed systems and enables direct connection to always-on rails. |
| VCC = 1V reset validity | RESET remains actively driven low down to 1V supply - ensures deterministic reset state during deep brownout or backup battery transition. |
| Power-supply transient immunity | Immune to VCC glitches ≤12µs at 100mV overdrive - avoids false resets in electrically noisy environments like motor drives or switching supplies. |
| No external components | Self-contained supervision with integrated comparator, timer, and output driver - reduces BOM count and layout complexity. |
Applications
| Bar-Code Scanners | Portable Medical Devices |
|---|---|
|
Use Scenario: Handheld scanner powers up from cold start with lithium battery at variable SOC; VCC ramps slowly under load. IC Role / Device Role / Timing Role: MAX821LUS monitors VCC rise, asserts RESET until stable >4.38V, then holds reset for 20ms (SRT=VCC) to ensure µP clock and memory initialization complete. Use Value: Prevents firmware crash during marginal battery startup by guaranteeing minimum reset hold time independent of VCC ramp rate. |
Use Scenario: Battery-powered glucose meter enters low-power sleep mode; wakes on button press with rapid VCC restoration from depleted cell. IC Role / Device Role / Timing Role: MAX821LUS detects VCC recovery, asserts RESET until 4.38V reached, then maintains reset for 100ms (SRT=open) to allow analog front-end settling and ADC calibration. Use Value: Eliminates need for software-controlled delay loops, reducing wake-up latency uncertainty and flash wear from repeated boot attempts. |
| Industrial PLC I/O Modules | Automotive Body Control Units |
|
Use Scenario: Module powered from 24V-to-5V DC/DC converter subject to load dump transients and cold-crank dips. IC Role / Device Role / Timing Role: MAX821LUS continuously monitors 5V rail, reasserts RESET within 50µs of VCC falling below 4.38V, and holds reset for 1ms (SRT=GND) to force clean µC reboot. Use Value: Survives 12V cold-crank events where VCC dips to 3.5V for 50ms - ensures deterministic recovery without latch-up or undefined state. |
Use Scenario: BCM powers from vehicle battery with wide voltage range (6V–16V); experiences load dump spikes and alternator ripple. IC Role / Device Role / Timing Role: MAX821LUS supervises regulated 5V domain, ignores sub-12µs transients, asserts RESET only on sustained brownout, holding for 20ms to synchronize with CAN bus wake-up sequence. Use Value: Prevents CAN node desynchronization caused by partial µC initialization during ripple-induced voltage sags. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar microprocessor supervisory applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX809LUR-T | Fixed 4.63V threshold, no pin-selectable timeout (140ms fixed), SOT23-3 package, 1.6µA supply current. | Lacks programmable delay flexibility; requires PCB redesign for SOT23-3 footprint and single-supply configuration. | Choose when fixed long timeout suffices and board space is constrained - not drop-in for MAX821LUS due to pin count and timeout inflexibility. |
| TPS3808G33DBVR | 3.3V fixed threshold, adjustable timeout via external capacitor (1ms–10s), SOT23-6 package, 1.1µA supply current. | Requires external timing capacitor and additional PCB area; threshold mismatch for 5V systems necessitates level-shifting or redesign. | Select for ultra-low power or highly customized timeout needs - not functionally equivalent due to threshold and interface incompatibility. |
Compared with MAX821LUS, MAX809LUR-T trades timeout flexibility for lower quiescent current and smaller footprint, while TPS3808G33DBVR offers wider timeout range but introduces component dependency and threshold mismatch - MAX821LUS uniquely balances precision 4.38V monitoring, three deterministic delays, and minimal BOM in SOT143.
Availability
MAX821LUS is available at Aetrix Electronics and suitable for portable medical devices, industrial PLC modules, automotive body control units, bar-code scanners, and battery-powered instrumentation requiring stable component supply across extended temperature ranges.
Supply support for MAX821LUS 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 power, sensing, connectivity, and security applications - founded in 1983 and headquartered in San Jose, CA.
The MAX821LUS belongs to Maxim's µP supervisory product line, engineered specifically for deterministic power-on/brownout reset in space-constrained, battery-sensitive, and thermally demanding embedded systems.
FAQ
What is the exact reset threshold voltage for MAX821LUS and how tightly is it specified?
The MAX821LUS has a nominal reset threshold of 4.38V, with guaranteed accuracy of ±1.5% over the full operating temperature range (-40°C to +125°C). This specification is validated per Maxim's Electrical Characteristics table and ensures reliable assertion before downstream 5V logic drops below its minimum operating voltage, making MAX821LUS suitable for systems where supply regulation margin is tight.
How does the SRT pin configure the reset timeout delay on MAX821LUS?
The SRT pin on MAX821LUS selects one of three factory-trimmed timeout periods: connect SRT to GND for 1ms (maximum), to VCC for 20ms (minimum), or leave unconnected for 100ms (minimum). Capacitive loading on SRT must remain below 200pF when open to avoid unintended shorter delays - this behavior is confirmed in the "Setting the Reset Timeout Delay" section of the MAX821LUS datasheet.
Can MAX821LUS maintain a valid RESET output when VCC drops below 1.5V?
Yes - the MAX821LUS guarantees RESET remains a valid active-low signal down to VCC = 1V, with sufficient sink current (≥3.2mA at VTH(MIN)) to drive standard CMOS inputs. Below 1V, RESET transitions to high-impedance; for continuous validity to 0V, a 100kΩ pull-down resistor is recommended per Maxim's Application Information section.
Is MAX821LUS compatible with bidirectional µP reset pins such as those on the Motorola 68HC11?
Direct connection to bidirectional reset pins may cause contention; Maxim recommends inserting a 4.7kΩ series resistor between MAX821LUS RESET and the µP reset I/O to isolate drive sources. This configuration prevents indeterminate logic states and is explicitly documented in Figure 3 of the MAX821LUS datasheet for safe interfacing with devices like the 68HC11 family.
What package type and dimensions does MAX821LUS use, and is lead-free packaging available?
MAX821LUS uses the SOT143-4 package (1.3mm × 2.1mm footprint, 0.95mm height) with pin 1 marked by a dot. Lead-free versions are available as MAX821LUS+T (tape-and-reel) or MAX821LUS+ (bulk), both using the same U4+1 package variant per Maxim's ordering information - standard leaded versions use suffix "-T" or no suffix (e.g., MAX821LUS-T).
MAX821LUS 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:
- 4.63V
- 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
MAX821LUS FAQ
1.How can I place an order for MAX821LUS through Aetrix?
Please submit a Request for Quotation (RFQ) for MAX821LUS 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 MAX821LUS reliable?
The price and inventory of MAX821LUS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MAX821LUS is usually 5 days.
3.What payment methods are accepted for MAX821LUS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MAX821LUS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MAX821LUS?
MAX821LUS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MAX821LUS 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 MAX821LUS?
For technical support, including MAX821LUS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MAX821LUS requirements.
6.How does Aetrix verify that MAX821LUS is sourced from the original manufacturer or authorized distributors?
All MAX821LUS 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 MAX821LUS meets industry standards.
7.What is the process for return or replacement of MAX821LUS?
All MAX821LUS units undergo pre-shipment inspection (PSI). If there is an issue with MAX821LUS, 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 MAX821LUS part is unused and in its original packaging.
Return procedure for MAX821LUS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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