LTC4008 Datasheet, PDF (18/24 Pages) Linear Technology – 4A, High Efficiency, Multi-Chemistry Battery Charger

LTC4008
APPLICATIO S I FOR ATIO
Disabling the Thermistor Function
If the thermistor is not needed, connecting a resistor
between DCIN and NTC will disable it. The resistor should
be sized to provide at least 10µA with the minimum voltage
applied to DCIN and 10V at NTC. Do not exceed 30µA.
Generally, a 301k resistor will work for DCIN less than 15V.
A 499k resistor is recommended for DCIN between 15V
and 24V.
Using the LTC4008-1 (Refer to Figure 10)
The LTC4008-1 is intended for applications where the
battery power is fully isolated from the charger and wall
adapter connections. An example application is a system
with multiple batteries such that the charger’s output
power passes through a downstream power path or
selector system. Typically these systems also provide
isolation and control the wall adapter power. To reduce
cost in such systems, the LTC4008-1 removes the re-
quirement for the wall adapter INFET function or blocking
diode. Wall adapter or ACP detection is also removed
along with micropower shutdown mode. Asserting of the
SHDN pin only puts the charger into standby mode.
Failure to isolate the battery power from ANY of the
LTC4008-1 pins when wall adapter power is removed or
lost will only drain the battery at the IC quiescent current
rate. More specifically, high current is drawn from the
DCIN, CLP and CLN pins. Suggested devices to isolate
power from the charger include simple diodes, electrical
or mechanical switches or power path control devices
such as the LTC4412 low loss PowerPath^TM controller.
Because the switcher operation is continuous under nearly
all conditions, precautions must be taken to prevent the
charger from boosting the input voltage above maximum
voltage values on the input capacitors or adapter. Z1 and
Q3 will shut down the charger if the input voltage exceeds
a safe value.
PowerPath is a trademark of Linear Technology Corporation.
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