LTM8062EVPBF LINER [Linear Technology], LTM8062EVPBF Datasheet - Page 14

• Manufacturer Part Number: LTM8062EVPBF
• Description: 32VIN, 2A ?Module Power Tracking Battery Charger
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTM8062
When charging at a 1C rate, t
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 terminates 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 V
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
The LTM8062 has a precondition mode, 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, normal full-
current charging can commence. The LTM8062 incorporates
90mV hysteresis to avoid 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 battery
re-enters precondition mode after one-eighth EOC.
When a bad-battery fault is triggered, the charge cycle
is suspended, and the CHRG status pin becomes high
impedance. The FAULT pin is pulled low to signal that a
fault has been detected.
Cycling the charger’s power or shutdown function initiates
a new charge cycle, but the LTM8062 charger does not
require a manual reset. Once a bad-battery fault is detected,
14
EOC
is commonly set to three
BAT
drops 2.5% from
a new timer charge cycle initiates if the BAT pin exceeds
the precondition threshold voltage. During a bad-battery
fault, a small current is sourced from the charger; removing
the failed battery allows the charger output voltage to rise
above the preconditioning threshold voltage and initiate a
charge cycle reset. A new charge cycle is started by con-
necting another battery to the charger output.
Battery Temperature Fault: NTC
The LTM8062 can accommodate battery temperature
monitoring by using an NTC (negative temperature
coefficient) thermistor close to the battery pack. The
temperature monitoring function is enabled by connect-
ing a 10kΩ, β ≈ 3380 NTC thermistor from the NTC pin
to ground. If the NTC function is not desired, leave the
pin open. The NTC pin sources 50μA, and monitors the
voltage dropped across the 10kΩ thermistor. When the
voltage on this pin is above 1.36V (0°C) or below 0.29V
(40°C), the battery temperature is out of range, and the
LTM8062 triggers an NTC fault. The NTC fault condition
remains until the voltage on the NTC pin corresponds to
a temperature within the 0°C to 40°C range. Both hot and
cold thresholds incorporate 20% hysteresis, which equates
to about 5°C. If higher operational charging temperatures
are desired, the temperature range can be expanded by
adding series resistance to the 10k NTC resistor. Adding
a 909Ω resistor will increase the effective temperature
threshold to 45°C, for example.
During an NTC fault, charging is halted and both status
pins are pulled low. If timer termination is enabled, the
timer count is suspended and held until the fault condi-
tion is cleared.
Thermal Foldback
The LTM8062 contains a thermal foldback protection feature
that reduces charge current as the IC junction temperature
approaches 125°C. In most cases, on-chip temperatures
servo such that any overtemperature conditions are relieved
with only slight reductions in maximum charge current.
In some cases, the thermal foldback protection feature
can reduce charge currents below the C/10 threshold.
In applications that use C/10 termination (TMR = 0V), the
LTM8062 will suspend charging and enter standby mode
until the overtemperature condition is relieved.
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