LTC4008_15 Datasheet, PDF (19/24 Pages) Linear Technology – 4A, High Effi ciency, Multi-Chemistry Battery Charger

LTC4008
APPLICATIONS INFORMATION
Disabling the Thermistor Function
If the thermistor is not needed, connecting a resistor be-
tween 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 requirement 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™
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.
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