LTC4008 datasheet(18/24 Pages) LINER

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LTC4008

4008fa

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.

APPLICATIO S I FOR ATIO

PowerPath is a trademark of Linear Technology Corporation.

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 10

µAwiththeminimumvoltage

applied to DCIN and 10V at NTC. Do not exceed 30

µA.

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-

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