IEC-EN60950-1 데이터 시트보기 (PDF) - Littelfuse, Inc

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IEC-EN60950-1

Use of Low Resistivity Surface Mount PPTC in Li-ion Polymer Battery Packs

Littelfuse, Inc 

Application Note:

Use of Low Resistivity Surface Mount PPTC

in Li-ion Polymer Battery Packs

● It is highly suggested that the application testing be

completed on the actual PCM board as the thermal

effects can vary quite signi cantly when compared

to a test board. The printed circuit board, traces,

solder pads, and even adjacent components all have

an effect on the thermal performance of the PPTC.

● The next step is to ensure the PPTC will trip or

activate fast enough to meet safety requirements.

Typically, smartphones and smaller tablets will need

to meet the standards in UL/IEC 60950-1, Limited

Power Source Sec 2.5. This standard will require the

PPTC to trip in ve seconds or less during an 8A fault

condition. In other words, the PPTC must limit

current to 8A or less in ve seconds or less.

● The nal critical aspect is the impedance of the PPTC

device. The higher the impedance (PPTC are purely

resistive components), the greater the drain on the

battery and the lower the total capacity or battery

“talk-time” energy available. Therefore, minimizing

the impedance is critical. The main advantage of

LoRhoTM PPTCs is their very low resistance compared

to standard PPTCs. However, all PPTCs undergo

what is called “trip jump” after experiencing a

thermal event or short circuit event. Trip jump is a

permanent increase in resistance from initial

resistance as delivered on tape/reel to post-re ow

resistance. Therefore, it is very important to

determine the typical and maximum trip jump

associated with a given device and the process that

it undergoes in manufacturing.

● The true worst-case maximum resistance of the

PPTC needs to be determined. The suggested

application test is for the PPTC to be re owed onto

the actual PCM using the re ow oven pro le

selected for the assembly. If there are multiple

re ow passes and any dwell or cure times, then

these should be applied as well. The PPTC

resistance should then be measured one hour after

the re ow process by using the four-wire method.

References

IEC/UL/EN 60950-1 - Information Technology Equip-

ment Safety, Part 1: General Requirement

©2012 Littelfuse, Inc

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