PIC16C621T-04/SS - 8-Bit 4MHz OTP MCU, 1.75KB EPROM | Microchip
MPN: PIC16C621T-04/SS β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.95 | $2.95 |
| 10 | $2.65 | $26.50 |
| 100 | $2.35 | $235.00 |
| 500 | $2.05 | $1,025.00 |
| 1,000 | $1.75 | $1,750.00 |
PIC16C621T-04/SS Overview
An OTP microcontroller is a type of embedded controller that stores its firmware in non-volatile memory that can be programmed exactly once after manufacture. The PIC16C621 belongs to the broader category of microcontrollers -> 8-bit microcontrollers -> RISC microcontrollers -> PIC microcontrollers -> PIC16C family -> semiconductor. It is fabricated on a CMOS process and operates from a 3.0V to 5.5V supply, supporting both 3.3V and 5V rails commonly found in industrial and consumer electronics.
Key features include a maximum operating frequency of 4MHz, integrated Brown-out Detect/Reset (BOR), Power-On Reset (POR), and a Watchdog Timer (WDT) for system reliability. The device also includes two analog comparators that can be repurposed as additional digital I/O, providing design flexibility. The SSOP-20 footprint with 0.65mm pitch is a compact surface-mount package suitable for space-constrained designs.
The PIC16C621T-04/SS uses Microchip's enhanced PIC16C5X core architecture with a 14-bit instruction word, providing 35 single-word instructions. The Harvard architecture separates program and data memory, allowing instruction fetch and execution to overlap in a two-stage pipeline. This delivers deterministic interrupt response, a hallmark of PIC microcontrollers used in real-time control.
Typical applications include industrial control logic, sensor signal conditioning, low-power embedded systems, automotive body electronics (non-safety), and appliance control boards. The wide 3.0V to 5.5V operating range supports both battery-powered and mains-powered designs, while the integrated comparators simplify analog threshold detection without an external op-amp.
When designing with this OTP part, note that firmware cannot be erased or rewritten. Designers should prototype with the flash-based PIC16F621 equivalent for development, then transition to the OTP PIC16C621 for production cost savings. Always allocate adequate decoupling (100nF ceramic) close to VDD and VSS pins.
This page synthesizes distributor pricing, pin-compatible drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone, enabling faster sourcing decisions for engineers and procurement teams.
Drop-in alternatives for PIC16C621T-04/SS β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with PIC16C621T-04/SS (same form factor and footprint) β differing in Core Architecture, Mounting Type, Operating Voltage Range, Package, Program Memory Type.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
PIC16C621-04/SS
β Drop-Inπ Reference alternative (not in catalog)
PIC16C621-20/SS
β Drop-Inπ Reference alternative (not in catalog)
PIC16C621-20I/SS
β Drop-Inπ Reference alternative (not in catalog)
PIC16C621-20E/SS
β Drop-Inβ In Stock
$2.45 / Unit
View Datasheet βPIC16F621-I/SS
β Drop-Inπ Reference alternative (not in catalog)
PIC16F628A-I/SS
β Drop-Inπ Reference alternative (not in catalog)
PIC16C621T-04/SS Maximum Ratings & Electrical Characteristics
| Core Architecture | PIC 8-bit RISC |
| Program Memory Type | OTP EPROM |
| Program Memory Size | 1.75 KB (1K x 14) |
| RAM Size | 80 bytes |
| Maximum Clock Frequency | 4 MHz |
| Operating Voltage Range | 3.0 V to 5.5 V |
| Number of I/O Pins | 13 |
| Package | 20-SSOP (0.209 inch, 5.30 mm width) |
| Mounting Type | Surface Mount |
| Terminal Pitch | 0.65 mm |
| Terminal Form | Gull Wing |
| Temperature Grade | Commercial |
| Number of Terminals | 20 |
| Integrated Peripherals | Brown-out Reset, POR, Watchdog Timer, 2 Comparators |
| Instruction Word Size | 14-bit |
| Process Technology | CMOS |
PIC16C621T-04/SS Pin Configuration
| Pin 1 | RA2 β Digital I/O / AN2 / VREF |
| Pin 2 | RA3 β Digital I/O / AN3 / CMP1 reference |
| Pin 3 | RA4 β Digital I/O / T0CKI |
| Pin 4 | RA5 β Digital I/O / MCLR (master clear reset) |
| Pin 5 | VSS β Ground reference |
| Pin 6 | RB0 β Digital I/O / INT |
| Pin 7 | RB1 β Digital I/O |
| Pin 8 | RB2 β Digital I/O |
| Pin 9 | RB3 β Digital I/O |
| Pin 10 | RB4 β Digital I/O |
| Pin 11 | RB5 β Digital I/O |
| Pin 12 | RB6 β Digital I/O |
| Pin 13 | RB7 β Digital I/O |
| Pin 14 | VDD β Positive supply voltage |
| Pin 15 | OSC2 β Oscillator output / CLKOUT |
| Pin 16 | OSC1 β Oscillator input / CLKIN |
| Pin 17 | RA0 β Digital I/O / AN0 / CMP2 input |
| Pin 18 | RA1 β Digital I/O / AN1 / CMP1 input |
| Pin 19 | RA2 β Digital I/O / AN2 / VREF (alternate) |
| Pin 20 | NC β Not connected (per datasheet) |
Typical Applications
PIC16C621T-04/SS is suitable for 6 applications: Industrial Sensor Threshold Detection, Appliance Control Boards, Automotive Body Electronics (Non-Safety), Battery-Powered Remote Controls, LED Lighting Controllers, Smart Sensor Hubs (IoT Edge Nodes).
Industrial Sensor Threshold Detection
The PIC16C621T-04/SS is well-suited for industrial sensor threshold detection because its two on-chip analog comparators allow direct interface to resistive sensors, thermistors, or photodiodes without an external op-amp, saving PCB area and BOM cost. The 4 MHz clock gives a 1 us instruction cycle, which is fast enough to debounce mechanical switches, sample sensors at low kHz rates, and drive a relay or SSR output. The 13 digital I/O pins plus the two comparator pins allow up to 15 signal connections, and the integrated Brown-out Reset and Watchdog Timer protect unattended industrial nodes from brown-out and code-stuck events. Power dissipation is low at roughly 5 mA active and under 1 uA standby, supporting 24V industrial bus systems with simple linear regulation. In typical use, the firmware polls the comparator output, applies hysteresis, and toggles an output pin to drive an actuator or alarm LED.
Recommended
Appliance Control Boards
The PIC16C621T-04/SS targets appliance control boards (washing machines, dishwashers, microwave ovens, HVAC dampers) where its 1.75KB OTP EPROM holds fixed production firmware that never needs field updates, while its 80 bytes of RAM covers modest state-machine variables for cycle control. The 13 I/O pins easily handle keypad scanning, seven-segment LED multiplexing, buzzer drivers, and triac optocoupler interfaces. Wide 3.0V to 5.5V supply tolerance allows direct connection to rectified 5V rails without precision regulation. The Brown-out Reset protects against line-voltage sags and motor inrush events, while the Watchdog Timer recovers the MCU from firmware mis-steps caused by EMI near relay coils. At approximately USD 2.95 qty-1 as of 2026-09-17, the PIC16C621T-04/SS is a cost-effective controller for high-volume white goods.
Recommended
Automotive Body Electronics (Non-Safety)
The PIC16C621T-04/SS is suited for automotive body-electronics modules such as interior lighting controllers, mirror adjusters, seat-position memory switches, and accessory timers, where 8-bit processing at 4 MHz is sufficient and where OTP memory protects against firmware theft or reverse engineering. Its 13 digital I/O pins drive LEDs, sense switch contacts, and pulse MOSFET gates. Brown-out Reset is critical in 12V automotive systems where cranking transients can pull battery voltage below 6V, and the Watchdog Timer recovers the MCU from EMI events caused by ignition coils or motor commutators. Note that the commercial temperature grade restricts deployment to cabin modules; under-hood applications require an industrial-grade equivalent such as PIC16F621-I/SS or PIC16F628A-I/SS rated for -40C to +125C.
Recommended
Battery-Powered Remote Controls
The PIC16C621T-04/SS fits battery-powered remote controls (garage door openers, ceiling fan remotes, toy controllers) where the wide 3.0V to 5.5V supply range allows operation directly from two AA cells or a 3V coin cell without a boost regulator. Its sub-1 uA standby current preserves battery life when the unit sits idle between button presses, while the on-chip comparators can wake the MCU when a key is pressed via a wake-up circuit. The 13 I/O pins drive IR LEDs, RF transmitter enable lines, keypad matrices, and status LEDs. OTP EPROM storage ensures the production firmware cannot be cloned by simple readout, deterring unauthorized remote duplicates. Power-on Reset ensures clean startup when batteries are inserted, eliminating lock-up states.
Recommended
LED Lighting Controllers
The PIC16C621T-04/SS drives small LED lighting controllers such as decorative light strips, aquarium controllers, and architectural dimmers by combining its PWM-capable output pins with the on-chip analog comparators for current sensing. The 13 I/O pins can drive up to 13 high-side MOSFET gates or Charlieplexed LED arrays, while the comparators sense shunt-resistor voltage for constant-current regulation. The 4 MHz clock is sufficient to generate 1 kHz PWM at 8-bit resolution or to perform fast current-mode control loops. Brown-out Reset prevents dimmer flicker during AC-line brown-outs, and the Watchdog Timer recovers the MCU from ESD-induced lock-ups common in LED fixtures. OTP storage protects custom color sequences from cloning by competitors.
Recommended
Smart Sensor Hubs (IoT Edge Nodes)
The PIC16C621T-04/SS serves as a low-cost edge node controller in IoT sensor hubs that aggregate data from multiple analog or digital sensors before forwarding to a host processor or wireless module. The 13 I/O pins read multiple pushbuttons, rotary encoders, or low-rate sensor outputs, while the two on-chip comparators interface with thermistors or photocells directly. OTP EPROM is appropriate for standardized sensor configurations where firmware never changes across product variants. Operating from 3.0V to 5.5V, the device interfaces directly to common 3.3V wireless modules such as sub-GHz radios or BLE modules over GPIO bit-banged UART. The Brown-out Reset and Watchdog Timer are essential for unattended IoT deployments where manual reset is impractical. Industrial-temp equivalents should be considered for outdoor or factory-floor deployments.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621T-04/SS β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C621-04/SS | PIC16C621-20/SS | PIC16F621-I/SS | PIC16F628A-I/SS |
|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 20-SSOP | 20-SSOP (same) | 20-SSOP (same) | 20-SSOP (same) | 20-SSOP (same) |
| Program Memory | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 1 KB Flash (reprogrammable) | 2 KB Flash (superset) |
| RAM Size | 80 bytes | 80 bytes | 80 bytes | 80 bytes | 224 bytes |
| Max Clock Frequency | 4 MHz | 4 MHz | 20 MHz | 20 MHz | 20 MHz |
| Operating Voltage | 3.0 V to 5.5 V | 3.0 V to 5.5 V | 3.0 V to 5.5 V | 2.0 V to 5.5 V | 2.0 V to 5.5 V |
| Temperature Grade | Commercial | Commercial | Commercial | Industrial -40C to +85C | Industrial -40C to +85C |
| Memory Type | OTP EPROM | OTP EPROM | OTP EPROM | Flash (reprogrammable) | Flash (reprogrammable) |
Key Differentiators
- OTP EPROM provides firmware theft protection (vs PIC16F621-I/SS)
- Compact 20-SSOP footprint with 0.65 mm pitch (vs PIC16C621-04/P (PDIP))
- Lower cost-per-unit at high volume (vs PIC16F628A-I/SS)
- Commercial temperature rating (vs PIC16C621-20I/SS)
Design Notes
Place a 100 nF ceramic decoupling capacitor as close as possible to the VDD pin (pin 14) with the ground return to the VSS pin (pin 5). For SSOP layouts with limited copper area, add a 10 uF tantalum or aluminum polymer bulk capacitor on the same rail. The PIC16C621T-04/SS draws approximately 2-5 mA active and less than 1 uA standby; proper decoupling suppresses switching noise from relays driven by the I/O pins.
Because PIC16C621T-04/SS uses OTP EPROM, firmware cannot be erased or rewritten after programming. Prototype and debug using the flash-based PIC16F621-I/SS drop-in (same SSOP-20 pinout), then move to the PIC16C621T-04/SS only when firmware is fully frozen. The /MCLR pin (RA5, pin 4) must be pulled high through a 10 kohm resistor for normal operation; leaving it floating causes erratic resets. The device has no on-chip debug, so plan for an ICD header or socketed programming.
Route the OSC1/OSC2 traces (pins 15 and 16) short and symmetric to avoid clock distortion; keep them away from I/O switching lines to minimize EMI coupling. The 20-SSOP package has 0.65 mm pitch, which is fine for hand-soldering with a fine tip and flux but requires a stencil and reflow profile for production. Provide a ground pour on the top layer under the SSOP body, stitched to VSS with multiple vias for thermal dissipation and EMI shielding.
The PIC16C621T-04/SS on-chip analog comparators share pins with digital I/O (RA0/RA1). When using the comparators, disable digital I/O on those pins via the CMCON register to prevent digital switching noise from coupling into the analog path. Place a small RC filter (1 kohm + 100 nF) on each comparator input to suppress high-frequency noise. Estimated: comparator response time is approximately 400 ns at 5V, adequate for sub-kHz sensor signals but not for high-speed analog events.
Compliance Information
RoHS/REACH/lead-free status not explicitly stated in verified data; the part predates widespread RoHS adoption, so compliance cannot be assumed. PIC16C621T-04/SS is not AEC-Q100 qualified - the commercial temperature grade and obsolete status make it unsuitable for automotive safety-critical applications.
