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
In this case, one can add resistance in series with
the thermistor to shift the range upwards, using the
following equation:
(VTHH/ITH) = kHOT(@40°C) × RNOM + R
R = (VTHH/ITH) - kHOT(@40°C) × RNOM
R = (2.5V/100µA) - 0.5758 × 6.8kΩ
Finally,
R = 5kΩ - 3.9kΩ = 1.1kΩ
This result shows that adding 1.1kΩ in series with
the thermistor sets the net resistance from TH to G
to be 0.5V at 40°C, satisfying VTHH at the correct
temperature. Adding this resistance, however, also
impacts the lower temperature limit as follows:
VTHL/ITH = kCOLD(@TC) × RNOM + R
kCOLD(@TC) = (VTHL/ITH) - R)/RNOM
Finally,
kCOLD(@TC) = (25kΩ - 1.1kΩ)/6.8kΩ = 3.51
Reviewing the characteristic curves, the lower
threshold is found to move to -5°C, a change of only
1°C. As a result, the system satisfies the upper
threshold of 40°C with an operating temperature
range of -5°C to 40°C, vs. our design target of 0°C
to 40°C. It is informative to highlight that due to the
NTC behavior of the thermistor, the relative impact
on the lower threshold is significantly smaller than
the impact on the upper threshold.
Fix VTHL
Following the same example as above, the
"unadjusted" results yield an operating temperature
range of -6°C to 33°C vs. the design goal of 0°C to
40°C. In applications that favor VTHL over VTHH,
however, one can control the voltage present at TH
at low temperatures by connecting a resistor in
parallel with ITH. The desired resistance can be
found using the following equation:
(ITH + (VCHG_IN - VTHL)/R) × kCOLD(@0°C) × RNOM = VTHL
Rearranging yields
R = (VCHG_IN - VTHL)/(VTHL/(kCOLD(@0°C) × RNOM) - ITH)
R = (5V - 2.5V)/(2.5V/(2.816 × 6.8kΩ) - 100µA)
R = 82kΩ
Adding 82kΩ in parallel with the current source
increases the net current flowing into the thermistor,
thus increasing the voltage at TH. Adding this
resistance, however, also impacts the upper
temperature limit:
VTHH = (ITH + (VCHG_IN - VTHH)/R) × kHOT(@40°C) × RNOM
Rearranging yields,
kHOT(@TC) = VTHH/(RNOM × (ITH + (VCHG_IN - VTHH)/R))
kHOT(@TC) = 0.5V/(6.8kΩ × (100µA + (5V - 0.5V)/82kΩ))
= 0.4748
Reviewing the characteristic curves, the upper
threshold is found to move to 45°C, a change of
Figure 12:
Fix VTHH Configuration
Figure 13:
Fix VTHL Configuration
Innovative PowerTM
ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of NXP.
- 47 -
www.active-semi.com
Copyright © 2012 Active-Semi, Inc.
Share Link: 
