Datasheet

12
LTC1325
FUNCTIONAL DESCRIPTIO
UU
U
Bit 3: Maximum Cell Voltage (FMCV)
The MCV bit indicates when the battery cell voltage has
exceeded the preset limit. The bit is set when V
CELL
is
greater than the voltage at the MCV pin.
FMCV CONDITIONS
0V
CELL
< V
MCV
1V
CELL
> V
MCV
Bit 4: End Discharge Voltage (FEDV)
The EDV bit indicates when the battery cell voltage has
dropped below an internally preset limit. The bit is set
when the battery cell voltage at the output of the voltage
divider V
CELL
is less than 900mV.
FEDV CONDITIONS
0V
CELL
> 900mV
1V
CELL
< 900mV
Bit 5: High Temperature Fault (FHTF)
The HTF bit indicates when the battery temperature is too
high. Using a negative TC thermistor, the bit is set when
the voltage at the T
BAT
pin is less than the voltage at the
HTF pin.
FHTF CONDITIONS
0T
BAT
> V
HTF
1T
BAT
< V
HTF
Bit 6: Low Temperature Fault (FLTF)
The LTF bit indicates when the battery temperature is too
low. Using a negative TC thermistor, the bit is set when the
voltage at the T
BAT
pin is greater than the voltage at the
LTF pin.
FLTF CONDITIONS
0T
BAT
< V
LTF
1T
BAT
> V
LTF
Bit 7: Timeout (t
OUT
)
The t
OUT
bit indicates that the battery charging time has
exceeded the preset limit. The bit is set when the internal
timer exceeds the limit set by the command bits TO0, TO1
and TO2.
T
OUT
CONDITIONS
0 No Timeout Has Occurred
1 Timeout Has Occurred
Bit 8: Fail-Safe Occurred (FS)
The FS bit indicates that one of the fault detection circuits
halted the discharging or charging cycle. The bit is set
when an EDV, LTF, HTF, or t
OUT
fault occurs during
discharge. During charging, the bit is set when a MCV,
LTF, HTF, or t
OUT
fault occurs. The bit is reset by the
command word bit FSCLR.
FS CONDITIONS
0 No Fail-Safe Has Occurred
1 Fail-Safe Has Occurred
DETAILED DESCRIPTION
Fault Conditions
The LTC1325 monitors the battery for fault conditions
before and during discharge and charge (see Figure 3).
They include: battery removed/present (BATP), battery
reversed/shorted (BATR), maximum cell voltage exceeded
Figure 3. Fail-Safe or Fault Detection Circuitry
+
–
+
–
+
–
V
DD
BATP
FMCV
PROGRAMMABLE
BATTERY
DIVIDER
C2
C1
1.8V
C3
C4
+
–
FEDV
+
–
BATR
V
DD
V
BAT
SENSE
MCV
900mV
100mV
T
BAT
HTF
R4
R3 R
L
R
T
LTC1325 • F03
LTF
REG
REG
R
TRK
R1
R2
3.072V
LINEAR
REGULATOR
C5
+
–
FHTF
C6
+
–
FLTF
