LTC4067 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4067' PDF : 20 Pages View PDF
LTC4067
U
OPERATIO
if the battery is below the recharge threshold. There is
approximately 3°C of temperature hysteresis associated
with each of the input comparators. If the NTC pin is tied
to GND, thermistor qualified charging is disabled.
Fault Conditions
The ⎯C⎯H⎯R⎯G pin provides information as to the charging
status, indicating an active charge cycle with a strong
open-drain pull down at the ⎯C⎯H⎯R⎯G pin. NTC faults and
bad battery faults are indicated with serrated pulses; this
is described in more detail under the heading Fault Condi-
tions in the Applications Information section.
When the battery is being charged, the ⎯C⎯H⎯R⎯G pin is pulled
low by an internal N-channel MOSFET. When the charge
cycle enters voltage mode charging and the charge current
is reduced below ICC-CHG/10, the ⎯C⎯H⎯R⎯G indicates that the
charge cycle is nearly complete by switching to a Hi-Z
state. Also when the battery voltage exceeds the OUT
voltage and the input supply is removed, or the LTC4067
is put into suspend or shutdown modes, the ⎯C⎯H⎯R⎯G pin
is forced into a high impedance state. If a bad battery
is detected, or if an NTC temperature fault is detected,
charging is halted and the ⎯C⎯H⎯R⎯G pin switches to a series
of serrated open-drain pull down pulses. These serrated
current pulses are designed to cause an LED connected
from the ⎯C⎯H⎯R⎯G pin to a positive supply voltage to visibly
flash, indicating to the user that there is a problem, as well
as allowing a microcontroller to detect a fault condition
within 300μs.
Overvoltage Protection
The OVI input is provided to sense potentially hazardous
voltages at the input in case an unregulated wall adapter
is applied. If an overvoltage condition is detected the OVP
pin is driven high to turn off an external PMOS transistor
inserted in series with the IN pin to disconnect the high
voltage from the LTC4067.
Table 2 lists recommended P-channel MOSFETs to use
with the LTC4067.
Table 2. Recommended OVP Transistors
PART NUMBER
DESCRIPTION
IRLML6402
P-channel 16V
FDR8508P
Dual P-channel 16V
If the OVP pin is high, the power path from IN to OUT is
disabled.
4067f
14
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