Datasheet

Application information: monitoring and protection L6924D
26/38 Doc ID 11908 Rev 9
Based on Equation 16: and Equation 19: , it derives that:
Equation 20
The temperature hysteresis can be estimated by the equation:
Equation 21
Where V
TH
is the pin voltage threshold on the rising edge, V
TH_HYS
is the pin voltage
threshold on the falling edge, and NTC
T
(-%/°C) is the negative temperature coefficient of
the NTC at temperature (T) expressed in % resistance change per °C. For NTC
T
values, see
the characteristics of the NTC manufacturers (e.g. the 2322615 series by VISHAY). At the
low temperature, the hysteresis is approximately:
Equation 22
Obviously at the high temperature hysteresis is:
Equation 23
Considering typical values for NTC
0°C
and NTC
50°C
, the hysteresis is:
Equation 24
And:
Equation 25
If a PTC connected to GND is used, the selection is the same as above, the only difference
is when the battery temperature increases, the voltage on the TH pin increases, and vice
versa. For applications that do not need a monitor of the battery temperature, the NTC can
be replaced with a simple resistor whose value is one half of the pull-up resistor R
UP
.
In this case, the voltage at the TH pin is always inside the voltage window, and the charge is
always enabled.
7
50
0
=
°
°
CNTC
CNTC
R
R
TTH
HYSTHTH
HYS
NTCV
VV
T
×
−
=
_
CNTCmV
mVmV
T
CHYS
°×
−
=
°
0900
780900
0
CNTCmV
mVmV
T
CHYS
°×
−
=
°
50225
248225
50
C
mV
mVmV
T
CHYS
o
5.2
051.0900
780900
0
≅
×
−
=
°
C
mV
mVmV
T
CHYS
o
5.2
039.0225
248225
50
−≅
×
−
=
°