LTC4000-1 Datasheet, PDF (21/40 Pages) Linear Technology – High Voltage High Current Controller for Battery Charging with Maximum Power Point Control

Applications Information
POSSIBLE POSSIBLE
OUTPUT INSTANT-ON
VOLTAGE RANGE VOLTAGE RANGE
NOMINAL OUTPUT VOLTAGE
NOMINAL FLOAT VOLTAGE ^100%
105%
100%
100%
MINIMUM PRACTICAL
OUTPUT VOLTAGE
LTC4000-1
86%
NOMINAL INSTANT-ON VOLTAGE
75%
MINIMUM PRACTICAL
INSTANT-ON VOLTAGE
81.6%
40001 F08
Figure 8. Possible Voltage Ranges for V_OUT and V_{OUT(INST_ON)} in Ideal Scenario
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.
BIAS
LTC4000-1
NTC
BAT
NTC RESISTOR
THERMALLY COUPLED
WITH BATTERY PACK
R3
C_BIAS
R_NTC
40001 F09
Figure 9. NTC Thermistor Connection
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 = ^{RNTC 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
40001f
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