ACT8810QJ62C-T View Datasheet(PDF) - Active-Semi, Inc
Part Name
Description
MFG CO.
'ACT8810QJ62C-T' PDF : 54 Pages View PDF
ACT8810
Rev 9, 15-Nov-12
ActivePathTM CHARGER
FUNCTIONAL DESCRIPTION CONT’D
charge timers resume.
The net resistance from TH to GA required to cross
the threshold is given by:
100µA × RNOM × kHOT = 0.5V → RNOM × kHOT = 5kΩ
100µA × RNOM × kCOLD = 2.5V → RNOM × kCOLD = 25kΩ
where RNOM is the nominal thermistor resistance at
room temperature, and kHOT and kCOLD are the ratios
of the thermistor's resistance at the desired hot and
cold thresholds, respectively.
Figure 11:
Simple Configuration
In each design example, we refer to the Vishay
NTHS series of NTCs, and more specifically those
which follow a "curve 2" characteristic. For more
information on these NTCs, as well as access to the
resistance/temperature characteristic tables referred
to in the example, please refer to the Vishay
website at http://www.vishay.com/thermistors.
Simple Solution
The ACT8810 was designed to accommodate most
requirements with very little design effort, but also
provides flexibility when additional control over a
design is required. Initial thermistor selection is
accomplished by choosing one that best meets the
following requirements:
RNOM = 5kΩ/kHOT, and
RNOM = 25kΩ/kCOLD
where kHOT and kCOLD for a given thermistor can be
found on its characteristic tables.
Design Procedure
When designing with thermistors it is important to
keep in mind that their nonlinear behavior typically
allows one to directly control no more than one
threshold at a time. As a result, the design
procedure can change depending on which
threshold is most critical for a given application.
Most application requirements can be solved using
one of three cases,
Taking a 0°C to 40°C application using a "curve 2"
NTC for this example, from the characteristic tables
one finds that kHOT and kCOLD are 0.5758 and 2.816,
respectively, and the RNOM that most closely
satisfies these requirements is therefore around
8.8kΩ. Selecting 10kΩ as the nearest standard
value, calculate kCOLD and kHOT as:
kCOLD = VTHL/(ITH × RNOM) = 2.5V/(100µA × 10kΩ) = 2.5
kHOT = VTHH/(ITH × RNOM) = 0.5V/(100µA × 10kΩ) = 0.5
Identifying these values on the curve 2
characteristic tables indicates that the resulting
operating temperature range is 2°C to 44°C, vs. the
design goal of 0°C to 40°C. This example
demonstrates that one can satisfy common
operating temperature ranges with very little design
effort.
1) Simple solution
2) Fix VTHH, accept the resulting VTHL
3) Fix VTHL, accept the resulting VTHH
The ACT8810 was designed to achieve an
operating temperature range that is suitable for
most applications with very little design effort. The
simple solution is often found to provide reasonable
results and should always be used first, then the
design procedure may proceed to one of the other
solutions if necessary.
Fix VTHH
For demonstration purposes, supposing that we
had selected the next closest standard thermistor
value of 6.8kΩ in the example above, we would
have obtained the following results:
kCOLD = VTHL/(ITH × RNOM) = 2.5V/(100µA × 6.8kΩ) = 3.67
kHOT = VTHH/(ITH × RNOM) = 0.5V/(100µA × 6.8kΩ) = 0.74
which, according to the characteristic tables would
have resulted in an operating temperature range of
-6°C to 33°C vs. the design goal of 0°C to 40°C.
Innovative PowerTM
ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of NXP.
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Copyright © 2012 Active-Semi, Inc.
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