LTC4156IUFD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC4156IUFD
Linear Technology
'LTC4156IUFD' PDF : 52 Pages View PDF
LTC4156
APPLICATIONS INFORMATION
Alternate NTC Thermistors and Biasing
The LTC4156 provides temperature qualified charging if a
grounded thermistor and a bias resistor are connected to the
NTC pin. Charging is paused if the temperature rises above
an NTC_HOT_FAULT limit or falls below an NTC_TOO_
COLD limit. By using a Vishay curve 2 thermistor and a bias
resistor whose value is equal to the room temperature resis-
tance of the thermistor (r25), the upper and lower tempera-
tures are preprogrammed to approximately 60°C and
0°C, respectively. The NTC_HOT_FAULT threshold also
optionally generates an interrupt.
With minor modifications to the thermistor bias network
as shown in Figure 9, it is possible to adjust either one
or both of the temperature thresholds with the constraint
that it is usually not possible to move the temperature
thresholds closer together. Intuitively, this would require
increased temperature sensitivity from the thermistor.
LTC4156
RBIAS
NTCBIAS
NTC
RTEMP_RANGE
T RNTC
4156 F09
Figure 9. Alternate NTC Bias Network
In the explanation below, the following notation is used.
r25
NTC thermistor value at 25°C.
RBIAS
Low drift bias resistor, connected between the
NTCBIAS and NTC pins.
RTEMP_RANGE
Optional dilution resistor, connected in series with
the thermistor.
αT
≡
rT
r25
Thermistor resistance ratio at any temperature T relative
to its reference temperature.
40
α
TOO
_
COLD
≡
rTOO _ COLD
r25
Thermistor resistance ratio at desired NTC_TOO_COLD
threshold temperature relative to its reference
temperature.
αHOT _ FAULT
≡
rHOT _ FAULT
r25
Thermistor resistance ratio at desired NTC_HOT_FAULT
threshold temperature relative to its reference tem-
perature.
αBIAS
≡
RBIAS
r25
Ratio of low drift bias resistor to r25.
α TEMP
_ RANGE
≡
RTEMP _RANGE
r25
Ratio of optional low drift dilution resistor to r25.
Note that r25, rT, rTOO_COLD and rHOT_FAULT and are
all resistance values of the thermistor at different
temperatures, while RBIAS and RTEMP_RANGE are actual
low drift resistors.
In all of the following calculations, it will be necessary to
determine the thermistor’s aT at various temperatures.
This parameter is dependent only upon the material prop-
erties of the thermistor. aT for a given thermistor and
temperature may be found in one of two ways. Thermistor
manufacturers often provide a lookup table relating aT to
temperature in their data sheets. For any temperature T,
aT may be referenced directly.
The second way to obtain aT for any T requires the use
of a modeling equation and a material constant specific
to the thermistor:
αT
=
b
e
1
T
−
1
T0
4156f
Share Link: 