PIC16LC621A-04/SS - 8-Bit 4MHz OTP MCU 1.75KB 20-SSOP | Microchip
MPN: PIC16LC621A-04/SS ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.2 | $3.20 |
| 10 | $2.85 | $28.50 |
| 100 | $2.5 | $250.00 |
| 500 | $2.18 | $1,090.00 |
| 1,000 | $1.95 | $1,950.00 |
PIC16LC621A-04/SS Overview
A microcontroller (MCU) is a single-chip computer that integrates a CPU, memory (program + data), and configurable peripheral interfaces. The PIC16LC621A belongs to the PIC16C mid-range architecture lineage, an 8-bit RISC core family that emphasizes deterministic instruction timing, low power consumption, and a small footprint - making MCUs ideal for embedded control, sensor reading, and actuator driving. As an OTP variant, it is intended for production-volume applications where the firmware is finalized and code changes are not expected in the field.
Key differentiating features include a Harvard RISC architecture with 14-bit instruction words, an analog comparator module with programmable reference, a 5-channel 8-bit ADC (depending on device variant), in-circuit serial programming (ICSP) capability, and an extremely low standby current that enables battery-powered designs. The 13 I/O pins each source or sink up to 25 mA, providing direct drive capability for LEDs, relays, and small solenoids without external buffers.
At the architecture level, the PIC16LC621A uses a Harvard design with separate program and data buses, eliminating instruction-fetch contention with data access and delivering predictable single-cycle execution for almost every instruction. The OTP program memory (1.75 KB) stores firmware permanently after programming, while the 96-byte SRAM holds runtime variables. The integrated analog comparator simplifies threshold detection for battery, sensor, or signal-level applications.
Typical applications include low-power consumer appliances, sensor interface nodes, battery chargers, LED controllers, remote-control transmitters, and simple industrial timers. The 4 MHz version (-04) is the lower-speed member of the family, optimized for cost-sensitive designs that do not require the full 20 MHz performance of the -20 sibling.
When designing with this MCU, allocate at least one I/O pin for ICSP (typically RB6/RB7) to allow in-system firmware updates during prototyping, even on OTP parts. Ensure the Vdd rise time meets the POR specification to guarantee clean startup.
This page synthesizes distributor pricing, drop-in same-package variants, and practical design notes not found in the manufacturer datasheet - including cross-brand compatibility assessment and lifecycle context.
Drop-in alternatives for PIC16LC621A-04/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 PIC16LC621A-04/SS (same form factor and footprint) — differing in Package, Core Architecture, Program Memory Type, Program Memory Size, Operating Temperature Range.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16LC621A-04I/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16LC621A-04E/SS
✅ Drop-In✓ In Stock
$1.45 / Unit
View Datasheet →PIC16LC621A-04/SO
✅ Drop-In✓ In Stock
$1.75 / Unit
View Datasheet →PIC16LC621AT-04/SS
✅ Drop-In✓ In Stock
$1.22 / Unit
View Datasheet →PIC16LC621-04E/SO
✅ Drop-In✓ In Stock
$1.18 / Unit
View Datasheet →PIC16LC620A-04/SS
✅ Drop-In✓ In Stock
$2.74 / Unit
View Datasheet →PIC16F628A-I/SS
✅ Drop-In✓ In Stock
$1.41 / Unit
View Datasheet →PIC16LC621A-04/SS Maximum Ratings & Electrical Characteristics
| Core Architecture | PIC16C 8-bit RISC (Harvard) |
| Program Memory Type | EPROM (OTP, one-time programmable) |
| Program Memory Size | 1.75 KB (1K x 14 words) |
| Data RAM | 96 bytes |
| Maximum Clock Frequency | 4 MHz |
| Instruction Cycle | 200 ns (single cycle, except branches) |
| Supply Voltage (Vdd) | 2.5 V to 5.5 V |
| I/O Pins | 13 |
| Package | 20-pin SSOP (5.30 mm body width) |
| Mounting Type | Surface Mount |
| Operating Temperature | 0 C to +70 C (commercial) |
| Timers | 1 x 8-bit Timer |
| Watchdog Timer (WDT) | Yes |
| Brown-Out Reset (BOR) | Yes |
| Power-On Reset (POR) | Yes |
| Analog Comparator | Yes (2 channels, programmable reference) |
| In-Circuit Serial Programming (ICSP) | Yes |
PIC16LC621A-04/SS Pin Configuration
| Pin 1 | RA2/MCLR/Vpp — PORTA bit 2 / Master Clear (reset) input / Programming voltage |
| Pin 2 | RA0/AN0 — PORTA bit 0 / Analog input 0 |
| Pin 3 | RA1/AN1 — PORTA bit 1 / Analog input 1 |
| Pin 4 | RA3/AN3/Vref — PORTA bit 3 / Analog input 3 / Voltage reference |
| Pin 5 | RA4/T0CKI — PORTA bit 4 / Timer0 clock input |
| Pin 6 | RB0/INT — PORTB bit 0 / External interrupt input |
| Pin 7 | RB1 — PORTB bit 1 |
| Pin 8 | RB2 — PORTB bit 2 |
| Pin 9 | RB3 — PORTB bit 3 |
| Pin 10 | RB4 — PORTB bit 4 |
| Pin 11 | RB5 — PORTB bit 5 |
| Pin 12 | RB6/PGC — PORTB bit 6 / ICSP clock (programming) |
| Pin 13 | RB7/PGD — PORTB bit 7 / ICSP data (programming) |
| Pin 14 | Vdd — Positive supply voltage (2.5 V to 5.5 V) |
| Pin 15 | Vss — Ground reference |
| Pin 16 | OSC2/CLKOUT — Oscillator output / clock out |
| Pin 17 | OSC1/CLKIN — Oscillator input / external clock in |
| Pin 18 | RA7/OSC1 — PORTA bit 7 / alternate oscillator input |
| Pin 19 | RA6/OSC2 — PORTA bit 6 / alternate oscillator output |
| Pin 20 | RA5/SS/AN4 — PORTA bit 5 / Slave Select / Analog input 4 |
Typical Applications
PIC16LC621A-04/SS is suitable for 6 applications: Battery-Powered Sensor Node, LED Lighting Controller, Remote Control Transmitter, Industrial Timer and Counter, Smart Appliance User Interface, Automotive Body Electronics (Legacy).
Battery-Powered Sensor Node
The PIC16LC621A-04/SS fits battery-powered sensor nodes because of its 2.5 V to 5.5 V wide supply range, allowing direct connection to 2x AA alkaline or single Li-ion cells across their discharge curve. Its Harvard RISC core and 200 ns single-cycle instruction execution let the MCU wake from sleep, sample a sensor, transmit a result, and return to sleep within milliseconds - extending coin-cell life to multi-year operation. With 13 I/O (25 mA each) and an integrated analog comparator, the part can directly interface to thermistors, photodiodes, or PIR sensors without external signal conditioning. Designers should leverage the WDT and BOR for unattended field reliability and use ICSP on RB6/RB7 for prototype firmware iteration despite the OTP program memory.
Recommended
LED Lighting Controller
The PIC16LC621A-04/SS is well-suited for LED lighting controllers where each of its 13 I/O pins can source or sink 25 mA - enough to directly drive indicator LEDs, low-current strings, or optocouplers that gate mains-side driver stages without external transistors. The 4 MHz clock and 1.75 KB OTP program memory comfortably host PWM routines, color-mixing tables, and dimming curves for architectural or accent lighting. Its 2.5 V minimum supply lets it run from a small buck-derived rail, while the analog comparator enables zero-crossing detection for triac dimmer compatibility. The 20-SSOP footprint fits densely populated driver boards where thermal headroom is shared with the LED power stage.
Recommended
Remote Control Transmitter
For infrared or RF remote control transmitters, the PIC16LC621A-04/SS offers a compact, low-cost control platform with enough program memory (1.75 KB OTP) to store multiple protocol stacks (RC5, NEC, SIRC) or custom command tables. Its 13 I/O pins can simultaneously drive an IR LED (25 mA direct drive), a status LED, a keypad matrix scan, and a configuration switch bank. The PIC16C RISC core executes precise carrier-frequency generation in software with cycle-accurate timing, eliminating the need for an external PWM peripheral. The 4 MHz maximum clock provides ample throughput for 38 kHz IR carrier generation while keeping active current under 2 mA at 3 V, preserving battery life across years of standby.
Recommended
Industrial Timer and Counter
The PIC16LC621A-04/SS serves industrial timer and counter applications where deterministic timing is more important than raw clock speed. Its integrated 8-bit Timer0 with prescaler supports long-duration timing chains (seconds to hours) without external counters, while the WDT provides fail-safe recovery if firmware locks up. The Brown-Out Reset and Power-On Reset ensure clean startup on industrial supplies with inductive switching transients. With 13 I/O, the MCU can directly scan a 4x4 keypad, drive a multiplexed 7-segment display, and read relay outputs - all within the 20-SSOP's compact footprint. The 0 C to +70 C commercial grade fits indoor panel-mount enclosures.
Recommended
Smart Appliance User Interface
In smart appliances, the PIC16LC621A-04/SS handles the human-machine interface (HMI) layer: keypad scanning, LCD segment driving via software, LED status indication, and buzzer control. Its 13 I/O pins are sufficient for a 3x4 matrix keypad plus 4 dedicated indicator LEDs and a piezo buzzer. The Harvard RISC core's deterministic 200 ns instruction cycle ensures glitch-free keypad debouncing and smooth LED PWM dimming without jitter. The integrated analog comparator can monitor a battery-low threshold or detect a door-open switch without an external op-amp. The 20-SSOP package's 5.30 mm body width fits inside the slim control panel of modern small appliances.
Recommended
Automotive Body Electronics (Legacy)
For legacy automotive body-electronics modules - such as interior lighting controllers, seat-position memory, or simple door-lock logic - the PIC16LC621A-04E/SS variant (extended temperature -40 C to +125 C) provides drop-in compatibility with the SSOP-20 footprint while operating across the full automotive temperature range. Its 13 high-current I/O can directly switch small relays, LEDs, and optocouplers that gate solenoids or motors. The Brown-Out Reset handles crank-cold-start voltage drops down to ~3 V without spurious resets, while the Watchdog Timer recovers from firmware lockups caused by load-dump EMI events. For new automotive designs, the AEC-Q100 qualified PIC16F variants are now preferred.
Recommended
Recommended Products Summary
Engineering reference data for PIC16LC621A-04/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16LC621A-04I/SS | PIC16LC621A-04E/SS | PIC16LC620A-04/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 | 1.75 KB OTP | 1.75 KB OTP | 0.875 KB OTP (-50%) | 4 KB Flash (+128%) |
| RAM | 96 bytes | 96 bytes | 96 bytes | 96 bytes | 224 bytes (+133%) |
| Max Clock | 4 MHz | 4 MHz | 4 MHz | 4 MHz | 20 MHz (+400%) |
| Operating Temperature | 0 C to +70 C | -40 C to +85 C (industrial) | -40 C to +125 C (extended) | 0 C to +70 C | -40 C to +85 C (industrial) |
| Program Memory Type | OTP EPROM | OTP EPROM | OTP EPROM | OTP EPROM | Flash (reprogrammable) |
| I/O Pins | 13 | 13 | 13 | 13 | 16 (+3) |
| Unit Price (qty 100) | $2.50 | $2.65 (+6%) | $3.10 (+24%) | $2.30 (-8%) | $2.80 (+12%) |
Key Differentiators
- Wide 2.5 V to 5.5 V supply range covers both 3.3 V and 5 V rails (vs PIC16C621A-04/SS (5 V only variant))
- Drop-in industrial and extended temperature variants share the exact SSOP-20 footprint (vs PIC16LC621A-04I/SS and PIC16LC621A-04E/SS)
- Easy migration path to flash-based PIC16F628A-I/SS with same SSOP-20 pinout (vs PIC16F628A-I/SS (modern flash replacement))
Design Notes
Estimated: For the 20-SSOP package, allocate at least 0.5 mm clearance around the part and route all 13 I/O traces with 0.15 mm/0.20 mm width on a 4-layer board with a continuous ground plane beneath the SSOP body. Place a 100 nF decoupling capacitor within 3 mm of the Vdd pin (pin 14) and a 10 uF bulk capacitor near the supply entry point. The MCLR/Vpp pin (pin 1) requires a 10 kohm pull-up to Vdd for normal operation and a low-impedance path to the ICSP programmer during code update.
The PIC16LC621A-04/SS draws approximately 2 mA active at 4 MHz / 5 V and less than 1 uA in sleep mode, per the Microchip datasheet DC characteristics. For battery-powered designs, configure the WDT to wake the MCU from sleep at fixed intervals rather than using continuous polling. Ensure Vdd rise time during power-on is faster than the POR specification to avoid the MCU starting up in an indeterminate state - add a 10 kohm pull-up and 100 nF capacitor on MCLR if the supply ramp is too slow.
Estimated: Because the PIC16LC621A uses OTP program memory, firmware cannot be changed after programming - order engineering samples (windowed CERDIP -JW variants) for code development, then commit to the OTP SSOP version only after firmware is finalized. Reserve pins RB6 and RB7 for ICSP clock and data - reassigning them to general-purpose I/O breaks in-system programming and forces socketed programming on a dedicated programmer. The PIC16LC621A 'LC' (low-voltage CMOS) variant is not interchangeable with the PIC16C621A 'C' (standard CMOS) variant in production designs - verify the silicon revision marked on the package.
When using the internal analog comparator on PORTA, avoid toggling adjacent digital I/O pins during conversion to minimize digital-coupling noise on the comparator inputs. The analog reference (RA3/AN3/Vref) should be bypassed with 100 nF + 10 uF capacitors if used as the comparator reference. For designs switching inductive loads (relays, solenoids), place a snubber (1N4148 + 100 nF RC) across each coil and keep the snubber ground return within 10 mm of the MCU ground pin to prevent inductive kickback from corrupting the MCU's supply rail.
Compliance Information
RoHS compliant per Microchip product page and JLCPCB listing. The PIC16LC621A-04/SS is not AEC-Q100 qualified; for automotive applications use AEC-Q100 qualified PIC16F equivalents or contact Microchip for the latest automotive-grade PIC16 part numbers. Lead-free (Pb-free) packaging confirmed per Microchip packaging specifications.
