Datasheet

L6924D Application information: monitoring and protection
Doc ID 11908 Rev 9 25/38
When the TH pin voltage rises and exceeds the V
MINTH
= 50% of V
REF
(900 mV typ), the
L6924D stops the charge, and indicates a fault by the status pins. The device re-starts to
charge the battery, only when the voltage at the TH pin goes under V
MINTH_HYS
= 780 mV
(typ).
For what concerns the high temperature limit, when the TH pin voltage falls under the
V
MAXTH
= 12.5% of V
REF
(225 mV Typ.), the L6924D stops the charge until the TH pin
voltage rises to the V
MAXTH_HYS
= 248 mV (Typ.).
When the battery is at the low temperature limit, the TH pin voltage is 900 mV. The correct
resistance ratio to set the low temperature limit at 0°C can be found with the following
equation:
Equation 14
Where R
UP
is the pull-up resistor, V
REF
is equal to 1.8 V, and R
NTC0°C
is the value of the
NTC at 0°C. Since at the low temperature limit V
MINTH
= 900 mV:
Equation 15
It follows that:
Equation 16
Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225 mV. The
correct resistance ratio to set the high temperature limit at 50°C can be found with the
following equation:
Equation 17
Where R
NTC50°C
is the value of the NTC at 50°C. Considering V
MAXTH
= 225 mV it follows
that:
Equation 18
Consequently:
Equation 19
CNTCUP
CNTC
REFMINTH
RR
R
VV
°
°
+
×=
0
0
CNTCUP
CNTC
RR
R
°
°
+
×=
0
0
8.19.0
UPCNTC
RR
=
°0
CNTCUP
CNTC
REFMAXTH
RR
R
VV
°
°
+
×=
50
50
CNTCUP
CNTC
RR
R
°
°
+
×=
50
50
8.1225.0
7
50
UP
CNTC
R
R =
°