MCP121T-270E/TT - 2.63V Voltage Supervisor, 1uA, SOT-23-3 | Microchip
MPN: MCP121T-270E/TT ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.78 | $0.78 |
| 10 | $0.71 | $7.10 |
| 100 | $0.55 | $55.00 |
| 500 | $0.46 | $230.00 |
| 1,000 | $0.4 | $400.00 |
| 3,000 | $0.32 | $960.00 |
MCP121T-270E/TT Overview
A voltage supervisor (also called a voltage reset IC, POR circuit, or supervisory circuit) belongs to the power management IC family. Voltage supervisors sit between a system power rail and the reset pin of a microcontroller, FPGA, DSP, or ASIC. Their role is to prevent code corruption and latch-up by guaranteeing that the host only begins executing (or resumes executing) when the rail is genuinely valid. The category hierarchy is: voltage supervisor -> supervisory circuit -> power management IC -> semiconductor IC. The MCP121 family is one of Microchip's CMOS-supervisor product lines, optimized for ultra-low quiescent current rather than adjustable threshold flexibility.
Key differentiating features include the 1.75 µA maximum quiescent current (per the MCP121 datasheet), an open-drain active-low RESET output that can be pulled up to any rail up to VCC, an internal hysteresis design that rejects brief VCC dropouts, and a fixed 2.63 V threshold variant (other MCP121 thresholds include 3.08 V, 4.38 V, and 4.63 V). The 80 ms minimum reset timeout gives downstream bulk capacitors time to fully charge before the MCU begins to execute code, and the CMOS output stage draws negligible current in either state.
Technically, the part is built on a standard CMOS process and uses a precision bandgap reference plus comparator to establish the trip point. The open-drain RESET pin requires an external pull-up resistor to the host's logic rail (commonly 10 kohm to 100 kohm), which allows the reset signal to be translated to a 1.8 V, 3.3 V, or 5 V domain independently of the 2.63 V supervisor rail. This is a useful property when the host MCU operates at a lower logic voltage than the supervisor's monitored rail.
Typical applications include microcontroller brown-out protection in battery-powered IoT sensors, smart-watch and wearable PMICs, handheld consumer electronics, fire-alarm and smoke-detector modules, and any 3.3 V Li-ion cell system where a low-current voltage supervisor is needed. The SOT-23-3 footprint and 1 µA Iq also make it appropriate as a redundant supervisor on space-constrained boards.
A key design consideration is the choice of pull-up resistor. Because the RESET pin is open drain, the external pull-up determines the rise time of the reset signal and therefore the reset de-assertion behavior. A 10 kohm pull-up is typical; larger values (100 kohm or more) save quiescent current but slow the edge and may need a small capacitor to filter noise.
This page synthesizes Microchip MCP121 datasheet specifications, real distributor pricing, drop-in alternative MPNs, and practical design notes that are not duplicated on the manufacturer's PDF.
Drop-in alternatives for MCP121T-270E/TT — 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:
MCP121T-300E/TT
✅ Drop-In📋 Reference alternative (not in catalog)
MCP121T-315E/TT
✅ Drop-In📋 Reference alternative (not in catalog)
MCP121T-475E/TT
✅ Drop-In📋 Reference alternative (not in catalog)
MCP102T-315E/TT
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
MCP103T-315E/TT
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
MCP131T-315E/TT
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
MCP121T-270E/TT Specifications
| Function | Voltage supervisor (reset generator) |
| Number of Voltages Monitored | 1 |
| Monitored Voltage (Threshold) | 2.63 V (nominal) |
| Reset Output Type | Open-drain / open-collector |
| Reset Polarity | Active-low (RST) |
| Reset Timeout (Minimum) | 80 ms |
| Supply Current (Quiescent, Max) | 1.75 µA |
| Supply Current (Quiescent, Typical) | 1 µA |
| Output Voltage Range (RST pull-up) | 0 V to VCC |
| Package / Case | SOT-23-3 |
| Mounting Type | Surface Mount |
| Packaging | Tape & Reel (TR) |
| RoHS Status | Compliant |
| Series | MCP121 |
MCP121T-270E/TT Pin Configuration
| Pin 1 | VCC — Supply voltage input (monitored rail) |
| Pin 2 | GND — Ground |
| Pin 3 | RST — Active-low open-drain reset output |
Typical Applications
MCP121T-270E/TT is suitable for 6 applications: Microcontroller Brown-Out Protection, Battery-Powered IoT Sensor Node, Wearable Device Power Management, Fire and Smoke Detector Module, Industrial Sensor and Factory Automation, Redundant Supervisor on Space-Constrained Board.
Microcontroller Brown-Out Protection
The MCP121T-270E/TT is the canonical supervisor for microcontroller brown-out protection in 3.3 V systems. The 2.63 V threshold trips well before the host MCU's brown-out detector (typically ~2.0 V) and the 80 ms reset timeout lets decoupling capacitors fully charge before code execution resumes. With a 1 µA typical quiescent current and SOT-23-3 footprint, the part adds negligible standby drain and PCB area, making it ideal for Li-ion-cell-powered designs.
Recommended
Battery-Powered IoT Sensor Node
For wireless sensor nodes powered by coin cells or thin-film batteries, the MCP121T-270E/TT's 1 µA typical supply current contributes essentially nothing to total system standby, while its 2.63 V threshold is well-matched to the discharge curve of a Li-MnO2 primary cell or a regulated 3.3 V output of a boost converter. The SOT-23-3 footprint sits comfortably next to the radio module's reset line.
Recommended
Wearable Device Power Management
In wearable bands and smartwatches, PCB area is at a premium and every microamp of standby current matters. The MCP121T-270E/TT's SOT-23-3 footprint saves board area versus SOT-23-5 or SC-70 supervisors, and its 1 µA typical Iq is several times lower than competing 3-pin reset ICs. The 2.63 V threshold monitors the Li-ion cell voltage, asserting reset before the cell voltage collapses and the host MCU enters an undefined state.
Recommended
Fire and Smoke Detector Module
Smoke and CO detectors must remain operational for years on a single 9 V or 3 V battery, making supervisor Iq critical. The MCP121T-270E/TT draws 1 µA typical and provides fail-safe brown-out detection for the detector's MCU. The 2.63 V threshold aligns with a regulated 3.3 V rail, and the open-drain output accommodates whatever logic level the detector's MCU family uses (5 V PIC or 3.3 V ARM Cortex).
Recommended
Industrial Sensor and Factory Automation
Industrial 4-20 mA loop-powered sensors and PLCs require reliable reset behavior across noisy 24 V rails that may be regulated down to 3.3 V or 5 V. The MCP121T-270E/TT's 80 ms minimum reset timeout rejects brief brown-out transients, and its open-drain output can be wire-ORed with other reset sources (watchdog, manual reset button) for redundant fault protection. The CMOS design tolerates the wide temperature swings typical of factory environments.
Recommended
Redundant Supervisor on Space-Constrained Board
When a primary MCU already has internal brown-out protection, a redundant external supervisor adds defense-in-depth against software-disabling of internal monitors. The MCP121T-270E/TT's tiny SOT-23-3 footprint fits next to the reset test point, and its 1 µA Iq makes adding it trivial to the system standby budget. Designers may also wire the open-drain RST to a logic analyzer header for in-system reset monitoring.
Recommended
Recommended Products Summary
Engineering reference data for MCP121T-270E/TT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MCP121T-300E/TT | MCP121T-315E/TT | MCP121T-475E/TT | MCP102T-315E/TT | MCP103T-315E/TT |
|---|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | SOT-23-3 | SOT-23-3 | SOT-23-3 | SOT-23-3 | SOT-23-3 | SOT-23-3 |
| Threshold Voltage | 2.63 V | 3.00 V | 3.15 V | 4.63 V | 3.15 V | 3.15 V |
| Quiescent Current (Typ) | 1 uA | 1 uA | 1 uA | 1 uA | 1 uA | 1 uA |
| Quiescent Current (Max) | 1.75 uA | 1.75 uA | 1.75 uA | 1.75 uA | 1.75 uA | 1.75 uA |
| Reset Output Type | Open-drain active-low | Open-drain active-low | Open-drain active-low | Open-drain active-low | Push-pull active-low | Push-pull active-high |
| Reset Timeout (Min) | 80 ms | 80 ms | 80 ms | 80 ms | 80 ms | 80 ms |
| Number of Voltages Monitored | 1 | 1 | 1 | 1 | 1 | 1 |
Key Differentiators
- Ultra-low 1 uA typical quiescent current (vs MCP121T-300E/TT)
- Threshold tailored to 3.3 V Li-ion systems (vs MCP121T-475E/TT)
- Open-drain reset allows rail domain translation (vs MCP102T-315E/TT (push-pull))
- Bare 3-pin reset (minimal feature overhead) (vs MCP131T-315E/TT (with watchdog))
Design Notes
Do not forget the external pull-up resistor on the open-drain RST pin. Without it, the reset signal will not pull high after the supervisor de-asserts, leaving the MCU in permanent reset. A 10 kohm pull-up to VCC is the typical starting value. For very low-current designs, a 100 kohm to 1 Mohm pull-up works but slows the rising edge and may need a small capacitor (10-100 pF) to filter switching noise on the reset line.
Place the MCP121T-270E/TT as close as possible to the host MCU's reset pin to minimize the loop area of the reset trace. A long reset trace acts as an antenna and may couple noise that falsely toggles the MCU's reset input. Keep the supervisor's VCC and GND pins star-connected to the same decoupling capacitor network that serves the MCU. For battery-powered designs, place the supervisor near the battery terminal to detect voltage sag before it reaches the LDO input.
While the supervisor itself draws only 1 uA typical, the pull-up resistor on RST continuously sources current when reset is asserted. Estimated: with a 10 kohm pull-up to 3.3 V and continuous reset assertion, the pull-up contributes 330 uA - orders of magnitude more than the supervisor Iq. In deepest-sleep scenarios, size the pull-up to 100 kohm or higher to keep the overall reset-path standby current below 50 uA.
The 80 ms reset timeout is a minimum, not a maximum - actual reset pulse width depends on VCC rise time and internal timing. If the application requires a precise reset pulse, an external RC network cannot extend it; instead, look at the MCP131 family which offers an adjustable timeout. Also note that the MCP121 detects only VCC, not a separate logic rail - if the MCU runs from a regulated voltage derived from VCC, monitor the upstream rail rather than the regulated output.
Compliance Information
RoHS compliance confirmed by distributor listings (DigiKey, Mouser). The MCP121T-270E/TT is not AEC-Q100 qualified; for automotive applications consider Microchip's automotive-grade voltage supervisors. Other compliance fields not specified in the verified datasheet excerpts - flagged as unknown.
