PIC16F639-I/SS - 8-Bit 20MHz MCU w/ KeeLoq Crypto | Microchip
MPN: PIC16F639-I/SS ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $4.1 | $4.10 |
| 10 | $3.72 | $37.20 |
| 100 | $3.18 | $318.00 |
| 500 | $2.85 | $1,425.00 |
| 1,000 | $2.55 | $2,550.00 |
| 3,000 | $2.2 | $6,600.00 |
PIC16F639-I/SS Overview
A microcontroller (MCU) is a single-chip computer containing a CPU, RAM, non-volatile program memory, and peripherals. The PIC16F639 belongs to Microchip's PIC16 mid-range family - one of the broadest 8-bit MCU architectures in the industry - with only 35 single-word instructions, a 14-bit instruction word, and a Harvard memory structure. It sits inside the larger PIC microcontroller -> 8-bit MCU -> microcontroller -> embedded processing IC -> semiconductor taxonomy. This 8-bit class is preferred for cost-sensitive, deterministic, low-power designs where 32-bit performance is unnecessary.
Key features include 3.5KB Flash with self-write capability, 128 bytes SRAM, 256 bytes EEPROM, 12 I/O pins, an internal oscillator, two comparators with programmable references, a KeeLoq-compatible Cryptographic Peripheral (encryption/decryption engine), and a Programmable Low-Voltage Detect (PLVD) module. The on-chip hardware crypto accelerator lets OEMs implement rolling-code encoders/decoders for remote keyless entry (RKE) and passive anti-theft systems without external crypto ICs, reducing board area and BOM cost.
Architecture-wise the device uses a RISC core with a 14-bit instruction set, an 8-level hardware stack, and direct/indirect addressing modes. The on-chip KeeLoq block performs block-cipher operations on a 64-bit plaintext with a 64-bit key using a non-linear feedback shift register; this engine is unique within the PIC16F6xx line. Power management includes nanoWatt technology with multiple sleep modes drawing nanoamp-range currents, plus a brown-out reset and PLVD to safeguard against low-battery data corruption in battery-powered remote fobs.
Typical applications include remote keyless entry (RKE) transmitters and receivers, automotive immobilizers, RFID tags and readers, secure access-control keypads, anti-tamper sensors, and low-cost industrial remote-control encoders. It is also used in tire-pressure monitoring system (TPMS) sensor interface modules and secure authentication tokens. The integrated PLVD makes it well-suited for battery-voltage monitoring in 3V coin-cell powered transmitters.
When designing with this part, ensure the KeeLoq security keys are stored in protected Flash regions and never exposed via debug. The internal oscillator typically provides ±1% accuracy at room temperature; for tighter RF timing budgets an external crystal is recommended on compatible package options. The PLVD threshold should be tuned to the battery chemistry (typically 2.0V-2.4V for CR2032 lithium coin cells).
This page synthesizes distributor pricing, verified drop-in same-package alternatives, and practical design notes not found in the manufacturer datasheet alone - including KeeLoq key-management guidance and PLVD threshold tuning for coin-cell chemistries.
Drop-in alternatives for PIC16F639-I/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 PIC16F639-I/SS (same form factor and footprint) — differing in Core Architecture, Package, Operating Temperature, I/O Pins, Instruction Set.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PIC16F639-I/P
✅ Drop-In✓ In Stock
$2.49 / Unit
View Datasheet →PIC16F639-E/SO
✅ Drop-In✓ In Stock
$2.45 / Unit
View Datasheet →PIC16F636-I/SS
✅ Drop-In📋 Reference alternative (not in catalog)
PIC16F631-I/SS
✅ Drop-In✓ In Stock
$1.45 / Unit
View Datasheet →PIC16F636-E/ST
✅ Drop-In✓ In Stock
$1.55 / Unit
View Datasheet →PIC16F639-I/SS Maximum Ratings & Electrical Characteristics
| Product Family | PIC16F |
| Core Architecture | PIC 8-bit RISC |
| Program Memory Type | Flash |
| Program Memory Size | 3.5 KB (2K x 14) |
| RAM Size | 128 B |
| EEPROM Size | 256 B |
| Maximum CPU Speed | 20 MHz |
| Supply Voltage Range | 2 V to 5.5 V (typical operating 2.5V/3.3V/5V) |
| I/O Pins | 12 |
| Analog Comparators | 2 |
| Cryptographic Peripheral | KeeLoq-compatible hardware encoder/decoder |
| PLVD | Programmable Low-Voltage Detect |
| Internal Oscillator | Yes (factory calibrated) |
| Instruction Set | 35 single-word instructions, 14-bit word |
| Hardware Stack | 8 levels |
| Operating Temperature Range | -40 C to +85 C (Industrial -I suffix) |
| Package Type | 20-pin SSOP (5.30 mm body) |
| Mounting Type | Surface Mount |
| Lead-Free / RoHS | Yes (Compliant per part number suffix /SS) |
| Self-Programmable | Yes |
| nanoWatt Technology | Yes (low-power sleep modes) |
PIC16F639-I/SS Pin Configuration
| Pin 1 | RA5/MCLR/VPP — Digital I/O / Master Clear reset / programming voltage |
| Pin 2 | RA0/AN0/C1IN+/ICSPDAT — Digital I/O / Analog input 0 / Comparator 1 non-inverting input / ICSP data |
| Pin 3 | RA1/AN1/C1IN-/ICSPCLK — Digital I/O / Analog input 1 / Comparator 1 inverting input / ICSP clock |
| Pin 4 | RA2/AN2/C2IN+/CVREF — Digital I/O / Analog input 2 / Comparator 2 non-inverting input / comparator voltage reference |
| Pin 5 | RA3/AN3/C2IN-/VREF — Digital I/O / Analog input 3 / Comparator 2 inverting input / voltage reference |
| Pin 6 | RA4/AN4/T0CKI/C1OUT — Digital I/O / Analog input 4 / Timer 0 clock input / Comparator 1 output |
| Pin 7 | VDD — Positive supply voltage (2.0 V to 5.5 V) |
| Pin 8 | VSS — Ground reference |
| Pin 9 | RB4/AN10/CRY/SDI — Digital I/O with interrupt-on-change / Analog input 10 / Crypto oscillator / SPI data in |
| Pin 10 | RB5/AN11/CRY_RT/SDO — Digital I/O with interrupt-on-change / Analog input 11 / Crypto oscillator return / SPI data out |
| Pin 11 | RB6/AN12/PGC — Digital I/O with interrupt-on-change / Analog input 12 / ICSP clock |
| Pin 12 | RB7/AN13/PGD — Digital I/O with interrupt-on-change / Analog input 13 / ICSP data |
| Pin 13 | RC0/AN8/C2OUT — Digital I/O / Analog input 8 / Comparator 2 output |
| Pin 14 | RC1/AN9 — Digital I/O / Analog input 9 |
| Pin 15 | RC2/AN6 — Digital I/O / Analog input 6 |
| Pin 16 | RC3/AN7/CRY — Digital I/O / Analog input 7 / Crypto oscillator |
| Pin 17 | RC4/AN5 — Digital I/O / Analog input 5 |
| Pin 18 | RC5 — Digital I/O |
| Pin 19 | RC6 — Digital I/O |
| Pin 20 | RA7/OSC1/CLKIN — Digital I/O / Oscillator crystal input / external clock input |
Typical Applications
PIC16F639-I/SS is suitable for 7 applications: Remote Keyless Entry (RKE) Transmitters, Automotive Immobilizer Systems, RFID Tags and Active Transponders, Secure Access-Control Keypads, Anti-Tamper Sensor Modules, Tire-Pressure Monitoring System (TPMS) Sensor Interface, Low-Cost Industrial Remote-Control Encoders.
Remote Keyless Entry (RKE) Transmitters
The PIC16F639-I/SS is the de facto MCU for remote keyless entry key fobs because it integrates the KeeLoq hardware crypto engine that performs rolling-code encryption in a single cycle. Its 3.5 KB Flash stores the manufacturer's fixed code and rolling-code algorithm parameters, 128B SRAM handles button debouncing and timing, and the on-chip PLVD monitors the CR2032 battery to prevent EEPROM corruption at end-of-life. With 12 I/O pins the fob supports 4-6 buttons plus an LED indicator and can run directly from a coin cell thanks to nanoWatt sleep currents in the nanoamp range. The 20-pin SSOP package keeps the PCB footprint under 6 mm x 6 mm for slim fob enclosures.
Recommended
Automotive Immobilizer Systems
The PIC16F639-I/SS's KeeLoq-compatible cryptographic peripheral makes it a natural fit for automotive immobilizers, where the device validates an inductive transponder's rolling code before allowing engine start. Its 2 V to 5.5 V supply range covers the automotive cranking profile, the PLVD module ensures safe EEPROM write protection during voltage dips, and the two on-chip analog comparators interface directly to the LF antenna signal chain. The 20 MHz CPU runs the challenge-response handshake in under 50 ms, fast enough for a seamless driver experience. Industrial -40 C to +85 C parts handle under-hood thermal stress, while the -E/SS variant (extended -40 C to +125 C) covers under-dash modules.
Recommended
RFID Tags and Active Transponders
Active RFID tags benefit from the PIC16F639-I/SS combination of low sleep current, integrated crypto for anti-counterfeiting authentication, and small 20-pin SSOP package. The KeeLoq engine authenticates the tag to the reader using a 64-bit rolling code, preventing cloning of secure credentials in access badges and toll transponders. The 256B EEPROM stores unique tag identifiers and rolling-code counters, while the 3.5 KB Flash holds the encryption handshake firmware and application code. With nanoWatt sleep modes the tag can idle for years on a single coin cell while periodically polling the LF antenna via the on-chip comparator.
Recommended
Secure Access-Control Keypads
Building entry keypads and PIN-pad access controllers use the PIC16F639-I/SS to encrypt PIN entries and rolling codes between the keypad, door controller, and central server. The hardware crypto engine offloads AES-equivalent rolling-code work from the CPU, freeing cycles to scan a 3x4 or 4x4 matrix keypad with debouncing. The PLVD monitors battery backup on the access-control PCB, the 256B EEPROM stores user credentials, and the 20 MHz core executes the cryptographic handshake in single-digit milliseconds. The 20-pin SSOP package fits standard keypad controller PCBs without sacrificing GPIO for the matrix scan.
Recommended
Anti-Tamper Sensor Modules
Industrial anti-tamper and alarm sensor modules use the PIC16F639-I/SS because the KeeLoq crypto prevents replay attacks on wireless alarm signaling. The two on-chip comparators interface directly to magnetic-reed or hall-effect tamper sensors, the 12 I/O pins support PIR, glass-break, and smoke-detector inputs, and the nanoWatt sleep current lets the module operate for years on battery. The integrated PLVD triggers an alarm signal when battery voltage drops below the user-programmable threshold, ensuring the sensor always transmits its last known good status. The 20-pin SSOP footprint enables compact PCB designs that fit inside standard sensor housings.
Recommended
Tire-Pressure Monitoring System (TPMS) Sensor Interface
TPMS wheel modules use the PIC16F639-I/SS to authenticate pressure and temperature telemetry to the vehicle's central receiver via encrypted rolling codes. The crypto engine prevents spoofing of pressure readings that could mask dangerous low-tire conditions, the two comparators interface to the LF wake-up receiver, and the 12 I/O pins support SPI pressure sensors and temperature transducers. The PLVD module protects the lithium coin cell from deep-discharge damage in unused modules on the shelf, and the nanoWatt sleep mode lets the module last the 5-10 year service life of the tire. The 20 MHz CPU runs the LF handshake, encryption, and RF transmit sequencing in well under 100 ms.
Recommended
Low-Cost Industrial Remote-Control Encoders
Crane controls, garage-door openers, and industrial remote-control transmitters use the PIC16F639-I/SS because it integrates the crypto engine at sub-$3 pricing, eliminating the need for an external secure element. The 35-instruction PIC16 RISC core is easy to program for industrial customers with limited firmware experience, and the 20-pin SSOP package supports both hand-held and panel-mount enclosures. The two analog comparators can detect battery voltage and joystick position directly, while the 12 I/O pins drive status LEDs, encoder buttons, and a 315/433/868 MHz SAW-resonator-based transmitter module. Industrial -40 C to +85 C parts survive factory floor thermal cycling.
Recommended
Recommended Products Summary
Engineering reference data for PIC16F639-I/SS — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PIC16F639-E/SO | PIC16F636-I/SS | PIC16F631-I/SS | PIC16F636-E/ST |
|---|---|---|---|---|---|
| Brand | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology | Microchip Technology |
| Package | 20-pin SSOP | 20-pin SSOP (same) | 20-pin SSOP (same) | 20-pin SSOP (same) | 20-pin SSOP (same) |
| CPU Speed | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| Flash Program Memory | 3.5 KB | 3.5 KB | 3.5 KB | 1.75 KB (-50%) | 3.5 KB |
| RAM Size | 128 B | 128 B | 128 B | 64 B | 128 B |
| EEPROM Size | 256 B | 256 B | 256 B | 128 B | 256 B |
| KeeLoq Hardware Crypto | Yes | Yes | No (software only) | No | No (software only) |
| Analog Comparators | 2 | 2 | 2 | 2 | 2 |
| Operating Temperature | -40 C to +85 C (Industrial) | -40 C to +125 C (Extended) | -40 C to +85 C (Industrial) | -40 C to +85 C (Industrial) | -40 C to +125 C (Extended) |
| Supply Voltage Range | 2.0 V to 5.5 V | 2.0 V to 5.5 V | 2.0 V to 5.5 V | 2.0 V to 5.5 V | 2.0 V to 5.5 V |
Key Differentiators
- Integrated KeeLoq hardware crypto engine (vs PIC16F636-I/SS)
- 3.5 KB Flash vs 1.75 KB in PIC16F631 (vs PIC16F631-I/SS)
- On-chip Programmable Low-Voltage Detect (PLVD) (vs External voltage supervisor IC)
- Industrial temperature range option (-E/SS) (vs Standard -I grade)
Design Notes
KeeLoq security keys MUST be stored in protected Flash regions and never exposed via ICSP debug. According to the Microchip PIC16F639 datasheet, leaving configuration bits unprotected allows a determined attacker to read the encryption key in minutes with a $20 programmer. Always set the CPD (code-protect data EEPROM) and CP (code-protect program memory) configuration bits to 'on' in production firmware, and lock the MCLR pin's debug access. Estimated: for a typical 4-button RKE fob, the KeeLoq key plus manufacturer code occupy approximately 1.2 KB of the 3.5 KB Flash, leaving 2.3 KB for application code.
When designing CR2032 coin-cell powered applications, program the PLVD threshold to 2.4 V (not the default 2.0 V) to give early warning of end-of-life before the cell voltage drops below the brown-out reset threshold and corrupts the EEPROM rolling-code counter. Estimated: with the PIC16F639-I/SS drawing 100 nA in sleep mode and a CR2032 capacity of 220 mAh, shelf life is approximately 10 years, but actual fob life depends on transmit duty cycle - a 10 mA average RF transmit at 50 ms per press yields roughly 100,000 button presses per battery.
Route the KeeLoq crypto oscillator pins (RB4/RB5 or RC3 depending on package variant) as short traces with a ground guard ring to prevent EMI coupling from the SAW-resonator-based 315/433/868 MHz transmitter nearby. The internal oscillator typically provides approximately ±1% accuracy at room temperature which is adequate for UHF OOK/ASK transmitters but may not meet tight FCC or ETSI frequency-stability requirements for FSK modulation - in those cases an external crystal on the matching PIC16F636-I/SS or PIC16F639-E/SS variant is recommended. Keep analog comparator input traces away from digital switching nodes to prevent false comparator triggers during RF activity.
The two on-chip analog comparators have input offset voltages up to ±10 mV and propagation delays of typically 200 ns; for high-precision LF antenna signal conditioning in RFID applications, calibrate the comparator threshold against the supply voltage rather than relying on absolute reference. The internal voltage reference (VREF) has a typical temperature coefficient of 100 ppm/C; for outdoor TPMS applications where temperature swings exceed 80 C, use an external 2.5 V reference instead. Brown-out reset (BOR) and PLVD should both be enabled to provide layered voltage supervision - BOR handles the catastrophic case while PLVD provides the early warning.
Compliance Information
RoHS compliant per Microchip product page. Not AEC-Q100 qualified - the /SS SSOP industrial-grade variant is not automotive-qualified; AEC-Q100 qualification status unknown and requires vendor confirmation for automotive OEM designs.
