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IEC-UL60950-1

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

100

10

1

0.1

0.01

0.001

1

10

100

1000

Current in Amperes

Figure 8. Time Current (TC) curves

Resistance of the PPTC device changes directly with

temperature. The rating of the PPTC is in uenced by

ambient temperature, as shown at the temperature

de-rating chart (Figure 9). The heat required to trip the

device may come from several sources, such as:

● Resistive heating from the electrical current

● Ambient environment

● Adjacent components

170%

150%

130%

110%

90%

70%

50%

30%

10%

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80

Temperature (°C)

Figure 9. A PTC (or PPTC) de-rating chart

Key Considerations in Selecting a PPTC

1. Determine the circuit’s operating parameters:

● Application temperature

● Hold current requirement

2. Select the PPTC device that will accommodate the

circuit’s maximum ambient temperature and normal

operating current.

● Compare the selected device’s maximum

electrical ratings with the circuit’s maximum

operating voltage and interrupt current.

● Determine time-to-trip.

● Verify ambient operating conditions.

● Verify the PPTC device dimensions.

3. PPTC resistances do shift during operation.

● Repetitive tripping/reset cycles will cause slight

changes in resistance.

©2012 Littelfuse, Inc

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