LTM8062/LTM8062A
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The LTM8062/LTM8062A are complete monolithic, mid-
power, power tracking battery chargers, addressing
high input voltage applications with solutions that use a
minimum of external components. The products can be
programmed for float voltages between 3.3V and 14.4V
(LTM8062) or between 3.3V and 18.8V (LTM8062A) with
just two external resistors, operating under a 1MHz fixed
frequency,averagecurrentmodestep-downarchitecture.A
2A power Schottky diode is integrated within the μModule
charger for reverse input voltage protection. A wide input
range allows the operation to full charge from an input
voltage up to 32V. A precision threshold on the RUN pin
allows the implementation of a UVLO feature by using a
simple resistor network. The charger can also be put into
a low current shutdown mode, in which the input supply
bias is reduced to only 15μA.
The LTM8062/LTM8062A employ an input voltage regula-
tion loop, which reduces charge current if a monitored
input voltage falls below a programmed level at the VINREG
pin. There is a 1% 100k resistor to GND at this pin. When
the LTM8062/LTM8062A are powered by a solar panel,
the input regulation loop is used to maintain the panel at
peakoutputpower.TheLTM8062/LTM8062Aautomatically
enter a battery precondition mode if the sensed battery
voltage is very low. In this mode, the charge current is
reduced to 300mA. Once the battery voltage climbs above
the internally set precondition threshold (2.3V at the ADJ
pin), the μModule charger automatically increases the
maximum charge current to the full programmed value.
The LTM8062/LTM8062A can use a charge current based
C/10 termination scheme, which ends a charge cycle
when the battery charge current falls to one-tenth the
programmed charge current. The LTM8062/LTM8062A
also contain an internal charge cycle control timer, for
timer-based termination. When using the internal timer,
the charge cycle can continue beyond the C/10 level to
top-off the battery. The charge cycle terminates when
the programmed time elapses, about three hours for a
0.68F timer capacitor. The CHRG status pin continues
to signal charging at a C/10 or greater rate, regardless of
which termination scheme is used. When the timer-based
schemeisused,theLTM8062/LTM8062Aalsosupportbad
battery detection, which triggers a system fault if a battery
stays in precondition mode for more than one-eighth of
the total programmed charge cycle time.
OncechargingterminatesandtheLTM8062/LTM8062Aare
not actively charging, the charger automatically enters a
low current standby mode in which supply bias currents
are reduced to 85μA. If the battery voltage drops 2.5%
from the full charge float voltage, the LTM8062/LTM8062A
engage an automatic charge cycle restart. The IC also au-
tomatically restarts a new charge cycle after a bad-battery
fault once the failed battery is removed and replaced with
another battery. The LTM8062/LTM8062A contain a bat-
tery temperature monitoring circuit. This feature, using a
thermistor,monitorsbatterytemperatureandwillnotallow
charging to begin, or will suspend charging, and signal
a fault condition if the battery temperature is outside a
safe charging range. The LTM8062/LTM8062A contain
two digital open-collector outputs, CHRG and FAULT,
which provide charger status and signal fault conditions.
These binary coded pins signal battery charging, standby
or shutdown modes, battery temperature faults and bad
battery faults. For reference, C/10 and TMR based charg-
ing cycles are shown in Figures 1 and 2.
OPERATION