ltc4007eufd-1-trpbf Linear Technology Corporation, ltc4007eufd-1-trpbf Datasheet - Page 12

• Manufacturer Part Number: ltc4007eufd-1-trpbf
• Description: 4a, High Efficiency, Standalone Li-ion Battery Charger
• Manufacturer: Linear Technology Corporation

OPERATIO
LTC4007
the timing resistor connected to R
closed to sample the thermistor:
The external RC network is driven to approximately 4.5V
and settles to a final value across the thermistor of:
This voltage is stored by C7. Then the switch is opened for
a short period of time to read the voltage across the
thermistor.
12
t
for R
V
SAMPLE
RTH FINAL
RT
(
= 309k
= 127.5 • 20 • R
)
=
U
4 5
R
.
TH
V R
•
+
R
NTC
TH
R
10k
9
TH
RT
• 17.5pF = 13.8ms,
(NOT TO
SCALE)
V
CLK
NTC
T
C7
0.47µF
, keeps switch S1
32.4k
R9
VOLTAGE ACROSS THERMISTOR
9
LTC4007
NTC
S1
D
C
Figure 3
Figure 4
Q
When the t
testing is stored in the D flip-flop (DFF). If the voltage at
NTC is within the limits provided by the resistor divider
feeding the comparators, then the NOR gate output will be
low and the DFF will set T
continue. If the voltage at NTC is outside of the resistor
divider limits, then the DFF will set T
will be shut down, FAULT pin is set low and the timer will
be suspended until T
+
–
–
+
COMPARATOR HIGH LIMIT
COMPARATOR LOW LIMIT
t
for R
t
HOLD
HOLD
–
+
t
SAMPLE
RT
= 10 • R
60k
45k
15k
= 309k
HOLD
~4.5V
4007 F03
interval ends the result of the thermistor
RT
CLK
TBAD
• 17.5pF = 54µs,
BAD
4007 F04
returns to zero (see Figure 4).
BAD
to zero and charging will
BAD
to one, the charger
4007fa