LTC4098EUDC-3.6 查看數據表（PDF） - Linear Technology
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LTC4098EUDC-3.6
Linear Technology
LTC4098EUDC-3.6 Datasheet PDF : 32 Pages
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LTC4098-3.6
OPERATION
by monitoring the PROG pin voltage and using the fol-
lowing equation:
IBAT
=
VPROG
RPROG
•
1030
In many cases, the actual battery charge current, IBAT, will
be lower than the programmed current, ICHG, due to limited
input power available and prioritization to the system load
drawn from VOUT.
Charge Status Indication
The CHRG pin indicates the status of the battery charger.
Four possible states are represented by CHRG which include
charging, not charging (or float charge current less than
programmed end of charge indication current), unrespon-
sive battery and battery temperature out of range.
The signal at the CHRG pin can be easily recognized as
one of the above four states by either a human or a mi-
croprocessor. An open-drain output, the CHRG pin can
drive an indicator LED through a current limiting resistor
for human interfacing or simply a pull-up resistor for
microprocessor interfacing.
To make the CHRG pin easily recognized by both humans
and microprocessors, the pin is either a DC signal of ON
for charging, OFF for not charging or it is switched at
high frequency (35kHz) to indicate an NTC fault. While
switching at 35kHz, its duty cycle is modulated at a slow
rate that can be recognized by a human.
When charging begins, CHRG is pulled low and remains
low for the duration of a normal charge cycle. When charge
current drops to 1/10th the value programmed by RPROG,
the CHRG pin is released (Hi-Z). The CHRG pin does not
respond to the C/10 threshold if the LTC4098-3.6 is in VBUS
current limit. This prevents false end-of-charge indications
due to insufficient power available to the battery charger. If
a fault occurs while charging, the pin is switched at 35kHz.
While switching, its duty cycle is modulated between a high
and low value at a very low frequency. The low and high
duty cycles are disparate enough to make an LED appear
to be on or off thus giving the appearance of “blinking.”
Each of the two faults has its own unique “blink” rate for
human recognition as well as two unique duty cycles for
machine recognition.
Table 2 illustrates the four possible states of the CHRG
pin when the battery charger is active.
Table 2. CHRG Signal
STATUS
Charging
IBAT < C/10
NTC Fault
Bad Battery
FREQUENCY
0Hz
0Hz
35kHz
35kHz
MODULATION
(BLINK) FREQUENCY
DUTY
CYCLES
0Hz (Low Z)
100%
0Hz (Hi-Z)
0%
1.5Hz at 50% 6.25% or 93.75%
6.1Hz at 50%
12.5% or 87.5%
Notice that an NTC fault is represented by a 35kHz pulse
train whose duty cycle toggles between 6.25% and 93.75%
at a 1.5Hz rate. A human will easily recognize the 1.5Hz
rate as a “slow” blinking which indicates the out of range
battery temperature while a microprocessor will be able
to decode either the 6.25% or 93.75% duty cycles as an
NTC fault.
If a battery is found to be unresponsive to charging (i.e.,
its voltage remains below 2.85V for 1/2 hour), the CHRG
pin gives the battery fault indication. For this fault, a human
would easily recognize the frantic 6.1Hz “fast” blink of the
LED while a microprocessor would be able to decode either
the 12.5% or 87.5% duty cycles as a bad cell fault.
Because the LTC4098-3.6 is a 3-terminal PowerPath
product, system load is always prioritized over battery
charging. Due to excessive system load, there may not
be sufficient power to charge the battery beyond the bad-
cell threshold voltage within the bad-cell timeout period.
In this case the battery charger will falsely indicate a bad
cell. System software may then reduce the load and reset
the battery charger to try again.
Although very improbable, it is possible that a duty cycle
reading could be taken at the bright-dim transition (low
duty cycle to high duty cycle). When this happens the
duty cycle reading will be precisely 50%. If the duty cycle
reading is 50%, system software should disqualify it and
take a new duty cycle reading.
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