PIC16C621A-04I/SO - 4MHz 8-Bit OTP MCU, 1.75KB | Microchip
MPN: PIC16C621A-04I/SO ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.2 | $3.20 |
| 10 | $2.86 | $28.60 |
| 100 | $2.51 | $251.00 |
| 500 | $2.24 | $1,120.00 |
| 1,000 | $1.98 | $1,980.00 |
PIC16C621A-04I/SO Overview
A microcontroller (MCU) is a single-chip computer that contains a CPU core, program memory, working RAM, and configurable I/O peripherals. The 8-bit PIC family uses a RISC Harvard architecture that separates program and data buses, allowing the CPU to fetch an instruction and a data operand in a single 200 ns cycle. This MCU category sits inside the broader microcontroller hierarchy: PIC mid-range -> 8-bit MCU -> microcontroller -> embedded processor -> semiconductor IC. Mid-range PIC16C parts are typically used where predictable real-time response and ultra-low cost are more important than raw throughput.
Key features include a wide 2.5 V to 5.5 V operating range, two on-chip analog comparators with programmable reference, an internal/external oscillator option, a 5-level hardware stack, and a 14-bit instruction set with only 35 single-word instructions. The /I suffix denotes the industrial temperature grade (-40 C to +85 C), and the /SO package designation specifies the 18-pin SOIC wide (300 mil) footprint supplied in tube packaging. The '04' designator marks the 4 MHz speed grade.
Architecturally, the device uses an enhanced mid-range core with separate program and data buses, an 8-bit ALU, and 8-level deep hardware stack for subroutine calls. Power management is supported by a wide Vdd range and a low-power Sleep mode with multiple wake-up sources (watchdog timer, external interrupt, comparators, and port change). The comparator peripheral provides direct analog signal conditioning without an external op-amp, simplifying designs that need threshold detection or zero-crossing sensing.
Typical applications include blood-pressure monitors, smoke detectors, consumer appliances, battery chargers, security panels, and general-purpose analog-front-end embedded controls. The internal comparators make it a good fit for sensor-threshold systems where an external ADC is unnecessary.
When designing with this MCU, plan for the OTP (one-time-programmable) memory limitation: code must be perfect before programming because the program memory cannot be erased and rewritten. For development, use a flash-based sibling (PIC16F62x) or a windowed ceramic package for iterative code work.
This page synthesizes distributor pricing, same-family drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for PIC16C621A-04I/SO — 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 PIC16C621A-04I/SO (same form factor and footprint) — differing in Analog Comparators, Package, Program Memory Size, RAM Size, Program Memory Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16F628A-04I/SO
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621A-04I/P
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$1.5 / Unit
View Datasheet →PIC16C621A-04/P
✅ Drop-In ⚠️ 参数待验证📋 Reference alternative (not in catalog)
PIC16C621A-20I/SO
✅ Drop-In✓ In Stock
$2.65 / Unit
View Datasheet →PIC16C620A-04I/SO
✅ Drop-In✓ In Stock
$2.55 / Unit
View Datasheet →PIC16C620-04I/SO
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$1.65 / Unit
View Datasheet →PIC16C621A-04I/SO Maximum Ratings & Electrical Characteristics
| Core Architecture | 8-bit PIC mid-range (RISC, Harvard) |
| Instruction Set | 35 single-word instructions (14-bit wide) |
| Maximum CPU Frequency | 4 MHz |
| Instruction Cycle Time | 200 ns (at 4 MHz) |
| Program Memory Type | OTP EPROM |
| Program Memory Size | 1.75 KB (1K x 14) |
| RAM | 96 bytes |
| Data EEPROM | 0 bytes (not present) |
| Operating Voltage (Vdd) | 2.5 V to 5.5 V |
| I/O Pins | 13 |
| Analog Comparators | 2 (with programmable reference) |
| ADC | None (0 channels) |
| Communication Peripherals | None (no UART, SPI, or I2C) |
| PWM Channels | 0 (stand-alone PWM) |
| Hardware Stack Depth | 8 levels |
| Package | 18-pin SOIC wide (SO, 300 mil) |
| Mounting Type | Surface Mount |
| Operating Temperature | -40 C to +85 C (industrial, /I grade) |
PIC16C621A-04I/SO Pin Configuration
| Pin 1 | RA2/AN2 — GPIO port A bit 2 / comparator input |
| Pin 2 | RA3/AN3 — GPIO port A bit 3 / comparator input |
| Pin 3 | RA4/T0CKI — GPIO port A bit 4 / Timer0 clock input |
| Pin 4 | MCLR/Vpp — Master clear reset (active low) / programming voltage |
| Pin 5 | Vss — Ground reference |
| Pin 6 | RB0/INT — GPIO port B bit 0 / external interrupt |
| Pin 7 | RB1 — GPIO port B bit 1 |
| Pin 8 | RB2 — GPIO port B bit 2 |
| Pin 9 | RB3 — GPIO port B bit 3 |
| Pin 10 | RB4 — GPIO port B bit 4 |
| Pin 11 | RB5 — GPIO port B bit 5 |
| Pin 12 | RB6 — GPIO port B bit 6 |
| Pin 13 | RB7 — GPIO port B bit 7 |
| Pin 14 | Vdd — Positive supply voltage (2.5 V to 5.5 V) |
| Pin 15 | OSC2/CLKOUT — Oscillator crystal output / clock out |
| Pin 16 | OSC1/CLKIN — Oscillator crystal input / external clock in |
| Pin 17 | RA0/AN0 — GPIO port A bit 0 / comparator input |
| Pin 18 | RA1/AN1 — GPIO port A bit 1 / comparator input |
Typical Applications
PIC16C621A-04I/SO is suitable for 6 applications: Blood Pressure Monitor, Smoke and Fire Detector, Battery Charger Controller, Consumer Appliance Control Board, Security and Alarm Panel, Sensor Signal Conditioning Front End.
Blood Pressure Monitor
The PIC16C621A-04I/SO fits blood pressure monitor designs because its two on-chip analog comparators can directly threshold the cuff pressure sensor signal without an external ADC. The MCU's 200 ns instruction cycle supports real-time inflation/deflation valve control loops, while the 1.75 KB OTP memory holds the inflation profile, pressure-decay averaging algorithm, and LCD driver state machine. Its 2.5 V to 5.5 V operation allows direct 3 V battery or 5 V USB-powered designs. Industrial temperature grade (/I) covers the home-healthcare storage and use range. Compared to a pure analog front end, the PIC16C621A reduces BOM cost by integrating the comparator, oscillator, and timing peripherals in one SOIC-18 package.
Recommended
Smoke and Fire Detector
The PIC16C621A-04I/SO is well suited for ionization-chamber smoke detectors. Its two comparators handle the chamber reference and alarm-threshold channels, while internal timers drive the piezo buzzer pulse patterns and LED indicator cadence. The 96 bytes RAM is sufficient for a moving-average baseline plus a peak-detect state machine. Wide 2.5 V to 5.5 V supply supports 9 V battery step-down or 3 V lithium primary cells, and Sleep mode with comparator wake-up extends battery life to multi-year operation. OTP memory protects the firmware from tampering, which is important for fire-safety certification in many jurisdictions. The 18-pin SOIC wide package fits the standard detector base footprint.
Recommended
Battery Charger Controller
In NiMH or lead-acid charger designs, the PIC16C621A-04I/SO provides the -delta-V termination comparator and timer-based charge-state sequencing. One comparator monitors the battery voltage through a divider, while the second handles current-sense thresholding for constant-current mode switching. The MCU's hardware stack and 200 ns cycle time keep the control loop deterministic under interrupt load. Industrial -40 C to +85 C operation covers garage and outdoor charger environments, while the 18-SOIC wide package supports reflow assembly. The OTP memory prevents end users from modifying charge parameters - useful for safety-certified consumer chargers. Sleep mode with wake-on-comparator minimizes idle draw when no battery is present.
Recommended
Consumer Appliance Control Board
The PIC16C621A-04I/SO fits white-goods control boards such as coffee makers, blenders, and toaster ovens. Its 13 GPIO pins can directly drive relay coils, triac gates, and seven-segment LED digits without external logic. The two comparators handle temperature-sensor (NTC) threshold detection and zero-cross detection for triac phase-angle control. The 1.75 KB OTP memory stores the menu state machine and timing profiles for specific models, and the OTP security feature prevents aftermarket firmware cloning. Industrial temperature grade tolerates the elevated ambient inside appliance housings. Wide 2.5 V to 5.5 V Vdd range simplifies power supply design when rectified mains is dropped to a regulated 5 V or 3.3 V rail.
Recommended
Security and Alarm Panel
The PIC16C621A-04I/SO is a good fit for wired alarm panel keypads and PIR sensor modules. Its 13 I/O pins handle multiple zone inputs, LED status indicators, piezo drivers, and the keypad scan matrix. The two comparators can monitor backup-battery voltage and PIR sensor thresholds directly. The 1.75 KB OTP memory secures the alarm protocol and prevents reverse-engineering of sensor ID encoding - a critical security feature. Wide operating voltage supports 12 V backup-battery systems with on-board regulation. Industrial temperature grade is suitable for outdoor PIR and unheated garages. Sleep current is low enough to support multi-year battery operation in wireless sensor variants.
Recommended
Sensor Signal Conditioning Front End
The PIC16C621A-04I/SO is used as a low-cost front-end MCU in industrial sensor transmitters, particularly 4-20 mA loop-powered and threshold-switch applications. Its two comparators handle zero-cross detection and trip-point comparison without an external op-amp, reducing the analog BOM. The 200 ns instruction cycle supports HART-style or simple PWM encoding for analog data transmission on top of a 4-20 mA loop. OTP memory locks the calibration coefficients and output transfer function in production, eliminating field-calibration drift. Industrial -40 C to +85 C temperature range meets process-control ambient specifications. The 18-SOIC wide package and reflow-compatible footprint support automated manufacturing at scale.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621A-04I/SO — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16F628A-04I/SO | PIC16C621A-04I/P | PIC16C621A-20I/SO | PIC16C620A-04I/SO |
|---|---|---|---|---|---|
| Package | 18-pin SOIC wide (SO) | 18-pin SOIC wide (SO) - same | 18-pin PDIP (P) - through-hole | 18-pin SOIC wide (SO) - same | 18-pin SOIC wide (SO) - same |
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Program Memory | 1.75 KB OTP EPROM | 3.5 KB Flash | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM |
| RAM | 96 bytes | 224 bytes | 96 bytes | 96 bytes | 96 bytes |
| Data EEPROM | 0 bytes | 128 bytes | 0 bytes | 0 bytes | 0 bytes |
| Max CPU Frequency | 4 MHz | 4 MHz | 4 MHz | 20 MHz | 4 MHz |
| Analog Comparators | 2 | 2 | 2 | 2 | 1 |
| Operating Voltage | 2.5 V to 5.5 V | 2.0 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V |
| I/O Pins | 13 | 16 | 13 | 13 | 13 |
| Lifecycle | NRND | Active | NRND | NRND | NRND |
Key Differentiators
- Two on-chip analog comparators with programmable voltage reference (vs PIC16C620A-04I/SO)
- Lower 2.5 V minimum supply voltage versus typical 3.0 V PIC16C620 (vs PIC16C620-04I/SO)
- Industrial -40 C to +85 C temperature grade in /I variant (vs PIC16C621A-04/SO (commercial 0-70C))
Design Notes
The PIC16C621A uses OTP EPROM program memory, which cannot be erased or rewritten once programmed. Estimated: a single device that fails programming is not recoverable - always validate the hex file with a flash-based PIC16F628A on the same PCB before committing to OTP production. For prototyping, use a windowed ceramic package (PIC16C621A-04/JW) so UV erasure is possible.
The PIC16C621A supply range is 2.5 V to 5.5 V. Place a 100 nF decoupling capacitor as close as possible to the Vdd pin (pin 14) and a bulk capacitor (10 uF tantalum or ceramic) at the regulator output. The MCU lacks a brown-out reset on older silicon revisions, so an external voltage supervisor (e.g., MCP100) is recommended for 3 V lithium-primary designs where slow voltage decay could corrupt GPIO state.
The 18-pin SOIC wide (300 mil) package is wider than the standard 150 mil SOIC. Reserve 300 mil of pad-to-pad clearance on the PCB. Keep the MCLR/Vpp (pin 4) trace short - long traces can pick up noise and trigger spurious resets. For ICSP programming, route RB6 (clock) and RB7 (data) to an in-circuit programming header. The MCLR pull-up resistor (typically 10 kohm) should be present even when not programming.
The PIC16C621A has two analog comparators whose inputs are multiplexed with GPIO RA0-RA3. Use the highest-impedance reference-divider resistors possible (100 kohm or larger) to minimize loading. The comparators can be configured to wake the MCU from Sleep, so decoupling on the analog supply rail is important - the on-chip bandgap reference is shared and may inject noise into the comparator inputs if Vdd is poorly regulated.
Compliance Information
RoHS and lead-free status are [DATA_NEEDED] from the verified distributor listings. Microchip's product page does not explicitly flag this part as RoHS-compliant; check the specific tube marking (Microchip ships OTP parts in both leaded and lead-free versions). Not AEC-Q100 qualified.
