PIC16C621A-04I/SS - 8-Bit 4MHz OTP MCU, 1.75KB | Microchip
MPN: PIC16C621A-04I/SS ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.97 | $2.97 |
| 10 | $2.75 | $27.50 |
| 100 | $2.45 | $245.00 |
| 500 | $2.2 | $1,100.00 |
| 1,000 | $1.98 | $1,980.00 |
PIC16C621A-04I/SS Overview
An 8-bit microcontroller (MCU) is a single-chip computer that integrates a CPU, program memory, data memory, and peripherals. The PIC16C family uses a RISC (Reduced Instruction Set Computer) architecture with only 35 single-word instructions, executed in 200 ns at 4 MHz (4 MHz oscillator) or as fast as 100 ns at higher speeds. The 'C' in PIC16C designates one-time-programmable (OTP) EPROM program memory, while the 'A' suffix denotes the second-generation silicon. OTP allows the device to be programmed once with application firmware using a device programmer, then locked for production use. As an EPROM technology, the PIC16C621A is intended for prototyping, low-volume production, and legacy designs where flash-based PIC16F parts have not yet been qualified.
Key features include 13 digital I/O pins, 2 analog comparators, a watchdog timer, power-on reset, brown-out detection, and an internal 4 MHz RC oscillator option. The wide 2.5 V to 6.0 V operating voltage range and -40 °C to +85 °C industrial temperature grade allow deployment in harsh embedded environments. Low-power operation is supported with typical current of 15 µA at 5 V / 4 MHz and 1 µA at 3 V / 32 kHz, making the PIC16C621A attractive for power-sensitive designs.
The PIC16C621A architecture pairs the PIC RISC core with dedicated peripheral modules including two on-chip analog comparators that can be combined with external passive components for ADC-style signal conditioning, plus a Timer0 8-bit counter/timer with programmable prescaler. The 14-bit instruction word is wider than typical 8-bit MCUs, providing constant opcodes that execute in a single cycle.
Typical applications include industrial control logic, sensor signal conditioning using the on-chip comparators, automotive body electronics subsystems, appliance control boards, and legacy embedded systems migrating from the original PIC16C621 (the A-suffix is the recommended replacement per Microchip migration document 41122B).
When designing with this part, choose the OTP variant for low-volume or legacy-validated designs; for higher-volume or field-reprogrammable needs, evaluate flash-based PIC16F621 or PIC16F628A equivalents that share the same SSOP-20 pinout. The device requires a programmer such as the MPLAB PM3 or PICkit 2/3 to load OTP firmware.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for PIC16C621A-04I/SS — 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/SS (same form factor and footprint) — differing in Operating Temperature Range, Program Memory Size, Program Memory Type, Watchdog Timer, Core Architecture.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16C621A-04/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16C621A-04E/SS
✅ Drop-In✓ In Stock
$1.4 / Unit
View Datasheet →PIC16C620A-04I/SS
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$2.55 / Unit
View Datasheet →PIC16C620A-20I/SS
✅ Drop-In ⚠️ 参数待验证✓ In Stock
$2.15 / Unit
View Datasheet →PIC16C621A-04I/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 | 96 bytes |
| Maximum CPU Speed | 4 MHz |
| Instruction Set Size | 35 single-word instructions |
| Operating Voltage Range | 2.5 V to 6.0 V |
| I/O Pins | 13 |
| Analog Comparators | 2 |
| Timers | 1 x 8-bit (Timer0 with prescaler) |
| Watchdog Timer | Yes |
| Oscillator Options | External RC, External Crystal, Internal 4 MHz RC |
| Brown-out Reset | Yes |
| Power-on Reset | Yes |
| Package Type | 20-pin SSOP (5.30 mm / 0.209 in) |
| Operating Temperature Range | -40 °C to +85 °C (Industrial, 'I' suffix) |
| Typical Operating Current (5 V, 4 MHz) | 15 µA |
| Typical Operating Current (3 V, 32 kHz) | 1 µA |
| Instruction Cycle Time at 4 MHz | 200 ns (minimum) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
PIC16C621A-04I/SS Pin Configuration
| Pin 1 | RA5/MCLR/VPP — Master Clear (reset) input / programming voltage |
| Pin 2 | RA0/AN0 — Bidirectional I/O / analog comparator input 0 |
| Pin 3 | RA1/AN1 — Bidirectional I/O / analog comparator input 1 |
| Pin 4 | RA2/AN2 — Bidirectional I/O / analog comparator input 2 |
| Pin 5 | RA3/AN3 — Bidirectional I/O / analog comparator input 3 |
| Pin 6 | RA4/T0CKI — Bidirectional I/O / Timer0 clock input (open drain) |
| Pin 7 | VSS — Ground reference |
| Pin 8 | OSC1/CLKIN — Oscillator input / external clock input |
| Pin 9 | OSC2/CLKOUT — Oscillator output / clock output (Fosc/4) |
| Pin 10 | RC0 — Bidirectional I/O port C bit 0 |
| Pin 11 | RC1 — Bidirectional I/O port C bit 1 |
| Pin 12 | RC2 — Bidirectional I/O port C bit 2 |
| Pin 13 | RC3 — Bidirectional I/O port C bit 3 |
| Pin 14 | RC4 — Bidirectional I/O port C bit 4 |
| Pin 15 | RC5 — Bidirectional I/O port C bit 5 |
| Pin 16 | RC6 — Bidirectional I/O port C bit 6 |
| Pin 17 | RC7 — Bidirectional I/O port C bit 7 |
| Pin 18 | VDD — Positive supply voltage |
| Pin 19 | RB7 — Bidirectional I/O port B bit 7 |
| Pin 20 | RB6 — Bidirectional I/O port B bit 6 |
Typical Applications
PIC16C621A-04I/SS is suitable for 7 applications: Industrial Control Logic, Sensor Signal Conditioning, Automotive Body Electronics, Appliance Control Boards, Legacy PIC16C621 Migration Designs, Low-Power Battery-Backed Embedded Nodes, Educational and Prototyping Boards.
Industrial Control Logic
The PIC16C621A-04I/SS fits industrial control logic boards because its 13 digital I/O pins, watchdog timer, and brown-out reset support reliable unattended operation in factory environments. With 1.75 KB of OTP program memory and 35 single-word RISC instructions, the part can implement state machines for relay control, conveyor sequencing, and discrete sensor logic without external glue logic. The -40 C to +85 C industrial temperature rating handles cabinet thermal rise, and the wide 2.5 V to 6.0 V supply tolerates 24 V industrial rails stepped down to 5 V. The 4 MHz instruction rate (200 ns cycle) is sufficient for sub-millisecond loop times typical in PLC-style control loops.
Recommended
Sensor Signal Conditioning
The PIC16C621A-04I/SS is well suited for sensor signal conditioning because it integrates two on-chip analog comparators that can be paired with external resistors to build window detectors, threshold switches, or simple RC-time-based ADC front-ends. With 13 I/O pins, the MCU can multiplex several sensors, drive status LEDs, and interface to a host via UART. The 96 bytes of RAM accommodate small filter windows for de-bouncing mechanical sensors. Low quiescent current (15 uA typical at 5 V / 4 MHz) is acceptable for line-powered instrumentation, while 1 uA at 3 V / 32 kHz supports battery-backed sensor nodes.
Recommended
Automotive Body Electronics
The PIC16C621A-04I/SS can be deployed in automotive body electronics subsystems such as interior lighting controllers, seat-position memory, mirror adjustment, and HVAC blend-door drivers. The 13 I/O pins are sufficient to read multiple switch inputs and drive low-side MOSFETs for loads like lamps and small motors. The watchdog timer and brown-out reset protect against automotive load-dump and cold-crank transients, while the industrial -40 C to +85 C grade covers cabin temperatures. Note: for under-hood applications exceeding +85 C, designers should select the PIC16C621A-04E/SS extended-temp variant. The OTP memory locks firmware at production, preventing field tampering.
Recommended
Appliance Control Boards
The PIC16C621A-04I/SS is a strong fit for white-goods and small-appliance control boards such as washing-machine timers, microwave oven keypads, dishwasher cycle controllers, and coffee-machine interfaces. The 1.75 KB OTP program memory holds typical appliance state machines including wash cycles, rinse sequences, and user-interface handling. The 13 I/O pins connect to mechanical keypads, 7-segment displays, triac-fired heater loads, and water-level sensors. Brown-out reset prevents erratic behavior during brown-outs when motors start, and the watchdog timer recovers from firmware lock-ups caused by EMI from relay switching.
Recommended
Legacy PIC16C621 Migration Designs
The PIC16C621A-04I/SS is the officially recommended replacement for the original PIC16C621 per Microchip migration document 41122B. Designs that already use the PIC16C621 in 18-pin DIP or 20-pin SSOP can migrate to the 'A' revision without code changes in most cases, benefiting from silicon revisions that fix early-erase window timing bugs and improve ESD performance. The 20-SSOP package variant is pin-compatible with the original PIC16C621-04I/SS, enabling drop-in PCB reuse for legacy maintenance contracts where the original part is now obsolete. Migration to the 'A' suffix also extends the lifecycle for industrial customers.
Recommended
Low-Power Battery-Backed Embedded Nodes
The PIC16C621A-04I/SS supports low-power battery-backed embedded nodes thanks to its 1 uA typical current at 3 V / 32 kHz operation, enabling multi-year battery life in sleep-dominant duty cycles. The 2.5 V to 6.0 V supply range accommodates 3 V lithium coin cells, two AA cells in series, or a small Li-ion pack. The 13 I/O pins can wake the MCU from sleep on a pin-change interrupt, allowing connection to motion sensors, pushbuttons, or RTC alarms. The brown-out reset prevents undefined operation when the battery droops, and the watchdog timer recovers from software hangs caused by ESD strikes during field deployment.
Recommended
Educational and Prototyping Boards
The PIC16C621A-04I/SS remains popular in university microcontroller courses and prototyping labs because the PIC16C family is the historical baseline taught in most EE programs. The 35-instruction RISC architecture lets students learn assembly fundamentals without a steep learning curve, and the 20-SSOP package is breadboard-friendly via SSOP-to-DIP adapters. The OTP EPROM memory forces students to commit to final firmware during lab sessions, mirroring real production workflows. The integrated analog comparators provide hands-on exposure to mixed-signal interfacing without external ADC ICs.
Recommended
Recommended Products Summary
Engineering reference data for PIC16C621A-04I/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16C621A-04/SS | PIC16C621A-04E/SS | PIC16C620A-04I/SS | PIC16C620A-20I/SS |
|---|---|---|---|---|---|
| Package | 20-SSOP (5.30 mm) | 20-SSOP (5.30 mm) - same | 20-SSOP (5.30 mm) - same | 20-SSOP (5.30 mm) - same | 20-SSOP (5.30 mm) - same |
| Brand | Microchip Technology | Microchip Technology - same | Microchip Technology - same | Microchip Technology - same | Microchip Technology - same |
| Program Memory | 1.75 KB (1K x 14) OTP EPROM | 1.75 KB OTP EPROM | 1.75 KB OTP EPROM | 896 B OTP EPROM (-49%) | 896 B OTP EPROM (-49%) |
| RAM Size | 96 bytes | 96 bytes | 96 bytes | 80 bytes (-17%) | 80 bytes (-17%) |
| Max Oscillator | 4 MHz | 4 MHz | 4 MHz | 4 MHz | 20 MHz (+400%) |
| Operating Voltage | 2.5 V to 6.0 V | 2.5 V to 6.0 V | 2.5 V to 6.0 V | 2.5 V to 6.0 V | 2.5 V to 6.0 V |
| I/O Pins | 13 | 13 | 13 | 13 | 13 |
| Temperature Grade | Industrial -40C to +85C | Commercial 0C to +70C | Extended -40C to +125C | Industrial -40C to +85C | Industrial -40C to +85C |
| Analog Comparators | 2 | 2 | 2 | 2 | 2 |
Key Differentiators
- Industrial temperature grade (-40C to +85C) in SSOP-20 (vs PIC16C621A-04/SS)
- Larger program memory than PIC16C620A family (vs PIC16C620A-04I/SS)
- Direct migration path from PIC16C621 original (vs PIC16C621-04I/P (DIP-18))
Design Notes
The PIC16C621A-04I/SS operates from 2.5 V to 6.0 V. Add a 100 nF decoupling capacitor within 5 mm of the VDD pin (pin 18) and a bulk capacitor (10 uF tantalum or ceramic) at the supply input. For battery applications drawing microamp-level sleep currents, place a 10 MOhm pull-up on MCLR (pin 1) only if an external reset source is needed; otherwise leave MCLR tied directly to VDD through a 10 kOhm resistor to minimize leakage. The internal brown-out reset trips at approximately 4.0 V on a 5 V supply, preventing code execution at unsafe voltages.
The PIC16C621A uses EPROM (OTP) technology, NOT flash. Once programmed, the firmware cannot be erased or rewritten. Always verify firmware with a known-good device programmer (MPLAB PM3, PICkit 2, or PICkit 3) BEFORE committing to production programming. Programming voltages for OTP parts are VPP=13 V typical on the MCLR pin. For development cycles, use the PIC16F621 (flash) instead - it is software-compatible and supports in-circuit reprogramming via ICSP.
In the 20-SSOP package, the oscillator pins (OSC1 pin 8, OSC2 pin 9) should be routed with short traces and surrounded by a ground pour to minimize EMI pickup. If using a crystal oscillator, keep the crystal and load capacitors (typically 15-33 pF) within 5 mm of the oscillator pins. The MCLR/VPP pin (pin 1) requires a 10 kOhm pull-up to VDD for normal operation and a low-impedance path to the programmer during OTP programming. Place a small-signal diode (e.g., 1N4148) from MCLR to VDD to clamp programming-voltage transients.
When using the two on-chip analog comparators, isolate the analog input pins (RA0-RA3) from switching digital traces. Add a small RC low-pass filter (10 kOhm + 100 pF) on comparator inputs in noisy environments such as motor-drive or relay-switching boards. The 13 digital I/O pins (RA0-RA7 except those used for comparators, RC0-RC7, RB6-RB7) can source or sink 25 mA per pin (100 mA total package limit) - derate to 10 mA per pin in practice to avoid latch-up in industrial environments.
The SSOP-20 (5.30 mm body) has a 0.65 mm pin pitch. Use a PCB land pattern with pad dimensions of approximately 0.40 mm x 1.55 mm and a thermal pad underneath not required (the SSOP-20 has no exposed pad). Apply a solder paste stencil of 0.15 mm thickness for reflow assembly. Hand-soldering of SSOP-20 is feasible with a fine-tip iron (0.5 mm) and 0.4 mm lead-free solder wire, but a hot-air rework station is preferred for rework.
Compliance Information
RoHS compliant per Microchip product page. AEC-Q100 not qualified - for automotive applications requiring qualification, use PIC16F621-E/SS or similar automotive-grade PIC16F flash parts. Lead-free per Microchip packaging marking.
