MCP1321T-20LI/OT - 2.0V Supervisor w/ WDI, SOT-23-5 | Microchip
MPN: MCP1321T-20LI/OT ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.42 | $1.42 |
| 10 | $1.18 | $11.80 |
| 100 | $0.92 | $92.00 |
| 500 | $0.78 | $390.00 |
| 1,000 | $0.65 | $650.00 |
MCP1321T-20LI/OT Overview
What is a voltage supervisor? A voltage supervisor (also called a reset IC, voltage monitor, or microprocessor supervisory circuit) is a power-management IC that monitors a system's supply rail and asserts a reset signal whenever the rail drops below a precise threshold. Supervisors sit between the power supply and the microcontroller's reset pin, complementing internal POR/BOD circuitry with higher accuracy (typically ±1-2%) and additional features such as watchdog timers, manual reset inputs, and complementary reset outputs. They belong to the broader category of power-management ICs and are essential whenever deterministic power-up / power-down behavior is required.
Key features of the MCP1321T-20LI/OT include: low supply current (microchip product page lists low-Iq operation), precision 2.0V ±1.5% (typical) trip point, watchdog input time-out of 1600 ms (L-option), reset delay of 200 ms (I-option), and complementary reset outputs. The open-drain /RESET line allows wired-OR connection with other supervisors or push-button reset circuits, while the active-high push-pull RESET drives a standard logic input directly without an external pull-up.
Technically, the device integrates a precision bandgap reference, a comparator, a counter for the watchdog timer, and an internal pull-up on /RESET. The WDI input must be toggled by the host MCU within the watchdog window; failure to do so asserts the reset outputs. Reset delay and WDI time-out are decoded from the device suffix (LI = 1600 ms WDI / 200 ms reset).
Typical applications include MCU brown-out protection in 3.3V and 5V systems, watchdog supervision of battery-powered sensors, embedded industrial controllers, IoT edge nodes, and any system requiring deterministic power-on reset behavior. Design consideration: the open-drain /RESET pin requires an external pull-up resistor to VDD, while the active-high RESET does not.
This page synthesizes distributor pricing, drop-in same-family alternatives, and practical design notes that are not found in the manufacturer datasheet alone.
Drop-in alternatives for MCP1321T-20LI/OT — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MCP1321T-30LE/OT
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MCP1321T-46CE/OT
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MCP1316T-20LI/OT
✅ Drop-In📋 Reference alternative (not in catalog)
MCP1321T-29LE/OT
✅ Drop-In📋 Reference alternative (not in catalog)
MAX6326XR22+T
✅ Drop-In📋 Reference alternative (not in catalog)
TPS3823-33DBVR
✅ Drop-In📋 Reference alternative (not in catalog)
MCP1321T-20LI/OT Specifications
| Function | Voltage supervisor with watchdog timer |
| Number of Supervisors Monitored | 1 |
| Trip Point Voltage (Vtrip) | 2.0 V |
| Reset Output 1 | Active-low, open-drain (/RESET) |
| Reset Output 2 | Active-high, push-pull (RESET) |
| Watchdog Timer (WDI) Time-out | 1600 ms |
| Reset Delay Time-out | 200 ms |
| Supply Current (Iq) | Low (per datasheet) |
| Operating Temperature Range | -40C to +85C (industrial, I-suffix) |
| Package | SOT-23-5 |
| Mounting Type | Surface Mount |
| Packaging | Tape & Reel (T-suffix) |
| Lead Finish | Pb-free (per product page) |
| RoHS Status | Compliant |
MCP1321T-20LI/OT Pin Configuration
| Pin 1 | /RESET — Active-low open-drain reset output |
| Pin 2 | GND — Ground |
| Pin 3 | WDI — Watchdog timer input |
| Pin 4 | RESET — Active-high push-pull reset output |
| Pin 5 | VDD — Supply voltage (monitored input) |
Typical Applications
MCP1321T-20LI/OT is suitable for 6 applications: MCU Brown-Out Protection (3.3V Systems), Watchdog Supervision for Industrial Controllers, Battery-Powered IoT Sensor Nodes, FPGA / CPLD Configuration Voltage Monitoring, Automotive Body Electronics (Non-Safety), Medical Monitoring Device Power Supervision.
MCU Brown-Out Protection (3.3V Systems)
The MCP1321T-20LI/OT monitors the 3.3V rail of an embedded MCU and asserts /RESET whenever VDD drops below 2.0 V, preventing code execution at indeterminate logic levels. With 200 ms reset delay (I-suffix), the part holds reset long enough for the MCU's oscillator and PLL to stabilize after power-up, eliminating lock-up from unstable boot code. The complementary open-drain and push-pull outputs let the designer wire /RESET to a system-wide reset net while feeding the push-pull output directly into the MCU's reset pin without a pull-up. Compared to internal MCU brown-out detectors, the MCP1321T-20LI/OT offers ±1.5% trip-point accuracy and a guaranteed reset delay.
Recommended
Watchdog Supervision for Industrial Controllers
Industrial controllers run firmware that may hang due to EMI, stack overflow, or peripheral lock-ups. The MCP1321T-20LI/OT's watchdog timer (WDI) requires the host firmware to toggle the WDI pin within 1600 ms (L-suffix); if firmware hangs, both reset outputs assert and the controller reboots. This is critical in PLCs, motor controllers, and factory automation where unattended lock-up can halt a production line. The 5-pin SOT-23 package saves board space versus discrete RC watchdog circuits and provides better timing accuracy.
Recommended
Battery-Powered IoT Sensor Nodes
IoT sensor nodes that sleep most of the time and wake on interrupt benefit from the MCP1321T-20LI/OT's low quiescent current and watchdog timer. When the node sleeps, the supervisor draws minimal Iq; on wake, the host MCU toggles WDI within 1600 ms to prove liveness, otherwise the supervisor asserts reset. The 2.0 V trip point suits 2-cell alkaline or single-cell Li-ion applications where the rail decays slowly toward end-of-life. A typical implementation places the supervisor between the battery and a 2.0 V LDO that powers the MCU.
Recommended
FPGA / CPLD Configuration Voltage Monitoring
FPGAs and CPLDs require their configuration supply rails to remain above a minimum voltage until configuration completes, otherwise the device latches up or loads garbage bitstreams. The MCP1321T-20LI/OT holds the FPGA's CONF_DONE or reset pin low via /RESET whenever the 2.0 V rail sags, preventing partial-configuration states. Designers commonly pair this supervisor with the FPGA's nCONFIG or PROGRAM_n pin in 1.8 V core-supply designs. The push-pull RESET output can drive the FPGA directly without external pull-up components.
Recommended
Automotive Body Electronics (Non-Safety)
Body-control modules such as seat controllers, mirror adjusters, and lighting drivers benefit from the MCP1321T-20LI/OT's industrial temperature grade (-40C to +85C) and robust watchdog supervision. While this part is not AEC-Q100 qualified, it provides deterministic reset behavior for 12V battery systems regulated down to 3.3V. The watchdog catches firmware lock-ups caused by load-dump transients that pass the LDO but confuse the MCU. For safety-critical ECUs, use an AEC-Q100 supervisor from Microchip's automotive portfolio instead.
Recommended
Medical Monitoring Device Power Supervision
Patient monitoring equipment such as portable pulse oximeters and wearable ECG patches require reliable MCU reset behavior because unexpected firmware lock-up could miss an alarm event. The MCP1321T-20LI/OT's watchdog timer forces recovery within 1.6 seconds, while its precision 2.0 V trip prevents operation at low battery. The compact SOT-23-5 package is suitable for wearable form factors. Designers should add additional ESD and EMI protection around the supervisor for IEC 60601-1 compliance.
Recommended
Recommended Products Summary
Engineering reference data for MCP1321T-20LI/OT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MCP1321T-30LE/OT | MCP1321T-46CE/OT | MCP1316T-20LI/OT | MCP1321T-29LE/OT | MAX6326XR22+T | TPS3823-33DBVR |
|---|---|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Maxim Integrated | Texas Instruments |
| Package | SOT-23-5 | SOT-23-5 | SOT-23-5 | SOT-23-5 | SOT-23-5 | SOT-23-5 | SOT-23-5 |
| Trip Point Voltage | 2.0 V | 3.0 V | 4.6 V | 2.0 V | 2.9 V | 2.2 V | 3.3 V |
| WDI Watchdog Time-out | 1600 ms | 1600 ms | different (C/E suffix) | 1600 ms | 1600 ms | varies by part | No WDI |
| Reset Delay | 200 ms | 200 ms | different (C/E suffix) | 200 ms | 200 ms | varies by part | 200 ms typical |
| Reset Output Type | Active-low OD + Active-high PP | Active-low OD + Active-high PP | Active-low OD + Active-high PP | Single (MCP1316 variant) | Active-low OD + Active-high PP | Active-low push-pull | Active-low push-pull |
| Watchdog Timer | Yes | Yes | Yes | Yes (MCP1316 family) | Yes | Optional per variant | No |
| Operating Temperature | -40C to +85C | -40C to +125C (E suffix) | 0C to +70C (C suffix) typical | -40C to +85C (I suffix) | -40C to +125C (E suffix) | -40C to +85C | -40C to +85C |
Key Differentiators
- Combined brown-out supervisor + watchdog timer in one chip (vs TPS3823-33DBVR)
- Complementary open-drain + push-pull reset outputs (vs MAX6326XR22+T)
- Family scalability across 2.0V-4.7V trip points (vs MCP1321T-46CE/OT)
Design Notes
Place the MCP1321T-20LI/OT as close as possible to the MCU's VDD and reset pins. Keep the trace from VDD (pin 5) to the MCU supply rail short (<10 mm) to minimize the parasitic inductance that could cause the supervisor to miss a fast voltage droop. Add a 0.1 uF decoupling capacitor directly at pin 5 (VDD) to GND (pin 2) to filter high-frequency noise that could falsely trigger the reset output.
The open-drain /RESET pin (pin 1) requires an external pull-up resistor to VDD; failing to install this pull-up leaves /RESET floating and unable to assert a logic-high idle level. Choose the pull-up value (typically 10 kohm to 100 kohm) based on the capacitive load and the desired rise time. Do not connect /RESET directly to a push-pull output of another device, as the wired-OR topology requires open-drain or open-collector drivers.
When the MCU firmware toggles the WDI pin (pin 3), ensure the toggle rate is faster than the 1600 ms watchdog window but slower than the minimum WDI pulse width specified in the datasheet. A watchdog serviced too frequently can mask a slowly failing MCU, while pulses narrower than the spec are ignored. The watchdog timer resets whenever a valid WDI edge is detected; sustained low or high levels will trigger reset after the time-out.
Compliance Information
RoHS compliant and Pb-free per Microchip MCP1321 product page. Industrial temperature grade (-40C to +85C) per I-suffix. Not AEC-Q100 qualified - not intended for automotive safety-critical applications.
