LTM8062/LTM8062A
15
8062fa
APPLICATIONS INFORMATION
of the programmed charge current. The FAULT pin signals
bad-battery and NTC faults. These pins are binary coded,
as shown in Table 3.
Table 3. Status Pin State
CHRG
FAULT
STATUS
High
Not Charging—Standby or Shutdown Mode
High
Low
Bad-Battery Fault (Precondition Timeout/EOC Failure)
Low
High
Normal Charging at C/10 or Greater
Low
NTC Fault (Pause)
If the battery is removed from an LTM8062/LTM8062A
charger that is configured for C/10 termination, a low
amplitude sawtooth waveform appears at the charger
output, due to cycling between termination and recharge
events. This cycling results in pulsing at the CHRG output.
An LED connected to this pin will exhibit a blinking pat-
tern, indicating to the user that a battery is not present.
The frequency of this blinking pattern is dependent on the
output capacitance.
C/10 Charge Termination
The LTM8062/LTM8062A support a low current-based
termination scheme, where a battery charge cycle termi-
nates when the charge current falls below one-tenth the
programmed charge current, or approximately 200mA.
ThisterminationmodeisengagedbyshortingtheTMRpin
to ground. When C/10 termination is used, an LTM8062/
LTM8062A charger sources battery charge current as
long as the average current level remains above the C/10
threshold. As the full-charge float voltage is achieved, the
charge current falls until the C/10 threshold is reached,
at which time the charger terminates and the LTM8062/
LTM8062A enter standby mode. The CHRG status pin fol-
lows the charger cycle and is high impedance when the
charger is not actively charging. There is no provision for
bad-battery detection if C/10 termination is used.
Timer Charge Termination
The LTM8062/LTM8062A support a timer-based termina-
tion scheme, where a battery charge cycle terminates after
a specific amount of time elapses. Timer termination is
engaged when a capacitor (CTIMER) is connected from the
TMR pin to ground. The timer cycle time span (tEOC) is
determined by CTIMER in the equation:
CTIMER = tEOC 2.27 10–7 (Hours)
When charging at a 1C rate, tEOC is commonly set to three
hours, which requires a 0.68μF capacitor.
The CHRG status pin continues to signal charging, regard-
less of which termination scheme is used. When timer
termination is used, the CHRG status pin is pulled low
during a charge cycle until the charge current falls below
the C/10 threshold. The charger continues to top off the
battery until timer EOC, when the LTM8062/LTM8062A
terminate the charge cycle and enters standby mode.
Termination at the end of the timer cycle only occurs if the
charge cycle was successful. A successful charge cycle
occurs when the battery is charged to within 2.5% of the
full-charge float voltage. If a charge cycle is not success-
ful at EOC, the timer cycle resets and charging continues
for another full timer cycle. When VBAT drops 2.5% from
the full-charge float voltage, whether by battery loading
or replacement of the battery, the charger automatically
resets and starts charging.
Preconditioning and Bad-Battery Fault
TheLTM8062/LTM8062Ahaveapreconditionmode,where
the charge current is limited to 15% of the maximum
charge current, or approximately 300mA. Precondition
mode is engaged if the voltage on the BAT pin is below the
precondition threshold, or approximately 70% of the float
voltage. Once the BAT voltage rises above the precondition
threshold,normalfull-currentchargingcancommence.The
LTM8062/LTM8062Aincorporate90mVhysteresistoavoid
spurious mode transitions.
Bad-battery detection is engaged when the internal timer
is used for termination (capacitor tied to TMR). This fault
detection feature is designed to identify failed cells. A
bad-battery fault is triggered when the voltage on BAT
remains below the precondition threshold for greater
than one-eighth of a full timer cycle (one-eighth EOC). A
bad-battery fault is also triggered if a normally charging
batteryre-enterspreconditionmodeafterone-eighthEOC.