Plastic-Encapsulated Chip PTC Thermistor

Plastic-encapsulated chip PTC thermistors are positive temperature coefficient thermistors (PTCs) packaged in surface mount technology (SMD) packaging. They are widely used in circuit protection, temperature sensing, and miniaturized electronic device designs. The following are their key features and selection considerations:
I. Core Features
‌Temperature Response Mechanism‌
At room temperature, the resistance is low (typically 1-20Ω). When the temperature exceeds the Curie point (e.g., 105°C), the resistance increases stepwise (up to several thousand ohms), providing self-current limiting.

The polymer matrix (PPTC) expands when overcurrent occurs, severing the conductive path and automatically recovering after the fault is resolved.

Product dimensions and recommended pad size

‌Packaging Advantages‌
Encapsulated with epoxy resin, they offer compact dimensions (e.g., 4524 and 2822 packages), making them suitable for high-density PCB layouts.
They are resistant to high temperatures and humidity, meet UL94-V0 flame retardancy standards, and are suitable for lead-free reflow soldering processes. RoHS Compliant
Suitable for lead-free wave soldering and reflow soldering of surface mount technology
Plastic encapsulated chip package, materials meet UL 94 V-0 flame retardancy requirements
Utilizes high-performance thermistor chip for compact size and high performance
Maintains stable performance over a long period of time
Wide operating temperature range: -40°C to 85°C

II. Selection Parameters

Parameters	Typical Value/Range	Description
Zero-Power Resistor	1-20Ω	Initial resistance affects circuit power consumption
Curie Temperature	75-250℃	Temperature threshold for triggering protection
Maximum Operating Voltage	≤250V	Must match circuit voltage level
Action Time	Milliseconds	Fast response to overcurrent or overtemperature events

III. Typical Applications
Electrical instruments;
Security equipment;
Communications equipment;
Home appliances;
Automotive electronics;
Other power products requiring overcurrent, overvoltage, and surge protection

Circuit Protection: For overcurrent protection of USB ports and battery packs.
Temperature Compensation: Linear PTC models (such as the CMZ series) simplify temperature compensation design for precision circuits.
Automotive electronics: Meets wide operating temperature range of -40°C to 200°C.

IV. Technical Comparison

Type	Advantages	Limitations
Ceramic PTC	High voltage resistance, high stability	Non-linear resistance-temperature curve
Polymer PPTC	Self-recovery, fast response	Low withstand voltage (typically ≤60V)

V. Mainstream Market Models

Item Model Specifications	Zero Power Resistance @ 25°C	Curie Temperature	Operating Current @ 25°C	Non-Operating Current @ 60°C	Maximum Current	Maximum Voltage
Item Model Specifications	Rn（Ω）	Tc（℃）	It（mA）	Ih（mA）	Imax（A）	Vmax（V）
SPSMD4032H450R#450	45	83±7	150	25	*	450
SPSMD3225H450R#300	45	83±7	100	18	*	300
SPSMD3225M450R#300	45	105±7	150	42	0.3	300
SPSMD3225M600R#300	60	105±7	130	38	0.3	300
SPSMD3225S121R#300	120	115±7	100	32	0.3	300
SPSMD3225S151R#450	150	115±7	95	28	0.3	450
SPSMD3225S251R#450	250	115±7	80	25	0.3	450
SPSMD3225S301R#450	300	115±7	70	20	0.3	450
SPSMD3225S501R#450	500	115±7	55	15	0.3	450
SPSMD40325S600R#420	60	115±7	160	45	0.8	420
SPSMD4032S800R#450	80	115±7	140	40	0.8	450
SPSMD4032S101R#450	100	115±7	120	35	0.8	450
SPSMD4032S151R#450	150	115±7	100	30	0.8	450
SPSMD4032S301R#450	300	115±7	80	25	0.8	450
SPSMD4032S501R#450	500	115±7	65	18	0.8	450
SPSMD3225H102R#550	1000	83±7	25	5	0.1	550
SPSMD3225H152R#650	1500	83±7	25	4	0.1	650
SPSMD3225H202R#650	2000	83±7	25	3	0.1	650

*SPSMD4032H450R#450 和SPSMD3225H450R#300 分别可用于 485 通讯接口保护抗 380VAC 和 220VAC。

‌JK-EK Series‌: 4524/2822 package, CQC/UL certified, suitable for LEDs and industrial equipment.

‌CMZL Series‌: Linear PTC, with controllable resistance-temperature gradient (±2000ppm/°C), suitable for automotive and medical applications.

Plastic-encapsulated chip PTC thermistors balance protection performance and space efficiency through an integrated design, making them an ideal solution for compact electronic devices.

VI. Precautions
General
To ensure the reliability of chip thermistors in actual use, extreme operating conditions should be considered during the design phase, and a certain margin should be allowed. Operating Environment
Ambient Temperature: -40-125°C
Relative Humidity: ≤95%
Atmospheric Pressure: 86-106 kPa
Vibration Frequency: 10-50 Hz
Acceleration: 98 m/s²

Storage
The chip thermistor should be stored in its original packaging. Do not open the packaging for storage.
Original Packaging Storage Conditions: Storage Temperature -25°C to +45°C, Annual Average Relative Humidity ≤75%, Maximum Not Exceeding 95%.
For chip thermistors, avoid contamination of the thermistor terminal surfaces during storage, handling, and processing.
SMD thermistors should be stored in environments that could affect their performance.
Use the chip thermistor within one year of receipt. After this time, recheck the solderability of the electrodes.

Transportation
The thermistor should be protected from dropping and impact during transportation.
It is recommended to wear gloves when handling the thermistor.
For chip thermistors, avoid contamination of the thermistor solder terminals during transportation.

Soldering (where applicable)
Sn96.5Ag3.0Cu0.5 solder paste is recommended.
Insufficient preheating may cause cracks in the thermistor ceramic chip.
The recommended maximum soldering temperature is 255±5°C for 3-6 seconds. Excessive soldering temperatures and extended soldering times may damage the thermistor.
Rapid cooling by immersion in solvent is not recommended.
After soldering, it is recommended to completely remove the flux or use a no-clean flux.