Datasheet
LTC4000-1
20
40001fa
For more information www.linear.com/LTC4001-1
Figure 8. Possible Voltage Ranges for V
OUT
and V
OUT(INST_ON)
in Ideal Scenario
NOMINAL OUTPUT VOLTAGE
POSSIBLE
OUTPUT
VOLTAGE RANGE
75%
86%
40001 F08
POSSIBLE
INSTANT-ON
VOLTAGE RANGE
105%
100%
100%
81.6%
NOMINAL FLOAT VOLTAGE
100%
NOMINAL INSTANT-ON VOLTAGE
MINIMUM PRACTICAL
OUTPUT VOLTAGE
MINIMUM PRACTICAL
INSTANT-ON VOLTAGE
applicaTions inForMaTion
output voltages that can be set for V
OUT(INST_ON)
and V
OUT
with respect to V
FLOAT
to ensure the battery can be fully
charged in an ideal scenario.
Taking into account possible mismatches between the
resistor dividers as well as mismatches in the various
regulation loops, V
OUT
should not be programmed to
be less than 105% of V
FLOAT
to ensure that the battery
can be fully charged. This automatically means that the
instant-on voltage level should not be programmed to be
less than 86% of V
FLOAT
.
Battery Temperature Qualified Charging
To use the battery temperature qualified charging feature,
connect an NTC thermistor, R
NTC
, between the NTC pin
and the GND pin, and a bias resistor, R3, from the BIAS
pin to the NTC pin (Figure 9). Thermistor manufacturer
datasheets usually include either a temperature lookup
table or a formula relating temperature to the resistor
value at that corresponding temperature.
Figure 9. NTC Thermistor Connection
NTC RESISTOR
THERMALLY COUPLED
WITH BATTERY PACK
R3
R
NTC
NTC
BIAS
BAT
LTC4000-1
40001 F09
C
BIAS
In a simple application, R3 is a 1% resistor with a value
equal to the value of the chosen NTC thermistor at 25°C
(R25). In this simple setup, the LTC4000-1 will pause
charging when the resistance of the NTC thermistor
drops to 0.54 times the value of R25. For a Vishay
Curve 2 thermistor, this corresponds to approximately
41.5°C. As the temperature drops, the resistance of the
NTC thermistor rises. The LTC4000-1 is also designed
to pause charging when the value of the NTC thermistor
increases to three times the value of R25. For a Vishay
Curve 2 thermistor, this corresponds to approximately
–1.5°C. With Vishay Curve 2 thermistor, the hot and cold
comparators each have approximately 5°C of hysteresis
to prevent oscillation about the trip point.
The hot and cold threshold can be adjusted by changing
the value of R3. Instead of simply setting R3 to be equal to
R25, R3 is set according to one of the following formulas:
R3 =
R
NTC
at cold_ threshold
3
or
R3 = 1.857 • R
NTC
at hot_ threshold
Notice that with only one degree of freedom (i.e. adjusting
the value of R3), the user can only use one of the formulas
above to set either the cold or hot threshold but not both.
If the value of R3 is set to adjust the cold threshold, the
value of the NTC resistor at the hot threshold is then