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polymer battery pack

The SMT form factor is optimized for Li-ion polymer

cell pack construction. Li-ion polymer packs are used

for low prole smartphone and tablet applications. The

SMT PPTC allows for more efcient high volume

manufacturing because the PPTC can be surface

mounted directly on the PCM (Protection Circuit

Module). Also, in low prole designs, the PCM board

is mounted at in the same plane as the polymer

pouch. This allows for the lowest prole thickness of

the smartphone or tablet design. The low height

choice for this application. The PPTC can be added to

the PCM while maintaining a minimum height prole

of the total assembly.

application testing aspects must be considered:

●

The overall space allocated for SMT PPTC needs to

be balanced against the total hold current required.

The designer rst needs to determine the maximum

continuous current (this includes burst use or peak

current use) and the maximum temperature that the

PPTC can experience (ambient temperature in the

PPTC’s vicinity).

●

So, the rst step in selecting the appropriate PPTC is

nding out how much current the device can hold at

the maximum temperature. The advantage of using a

amount of current in a relatively small form factor

and low prole device.

●

Application testing is suggested to verify that the

selected PPTC can hold the required current at

temperature. Typically, the device is subjected to the

required current for 15 minutes, which is enough

time to reach thermal stability. If device can hold the

current for 15 minutes, then this is one data point

that can be used to verify the correct device has

been selected.

Application Note:

Use of Low Resistivity Surface Mount PPTC

in Li-ion Polymer Battery Packs

●

Holding the device in a tripped state for long

periods of time will cause an increase in resistance.

●

Any hand soldering may have a signicant effect if

not performed properly and therefore is generally

not recommended (particularly for SMT

components)

4. PPTC devices have two distinct resistance ranges:

●

RMIN: the minimum resistance of un-soldered

devices

●

R1MAX: the maximum resistance of a device at

20°C, measured one hour after tripping or reow

soldering at 260°C for 20 seconds.

When measuring resistance:

●

Always perform the measurement at room

temperature.

●

Perform measurements at least one hour after

any heating process to ensure that the device has

cooled thoroughly (soldering, testing, etc.).

●

Keep in mind that catalog specications (trip time,

hold current, etc.) assume the parts have been

mounted on a PCB and the resistance shift has

already occurred.

Other critical considerations for component selection

include:

●

Maximum circuit voltage

●

Maximum available short circuit current

●

Desired trip current and trip time

●

Form factor

●

Maximum ambient operating temperature

●

Normal operating current

●

Maximum operating voltage

●

Maximum interrupt current