Datasheet

LTC4020
9
4020fd
For more information www.linear.com/LTC4020
is terminated or when charge current is below the C/10
threshold.
If the LTC4020 is configured for a CC charging algorithm,
the STAT1 pin is pulled low during the entire charging
cycle. The STAT1 pin becomes high impedance when the
charge cycle is terminated.
If the LTC4020 is configured for a lead-acid charging
algorithm, the STAT1 pin is used as a charge cycle stage
indicator pin, and pulled low during the bulk and absorp
-
tion charging stages. The pin is high impedance during the
float charging period and during NTC or bad batter
y faults
.
See Applications Information section.
STAT2 (Pin 13): Open-collector status output, typically
pulled up through a resistor to a supply voltage. This sta
-
tus pin can be pulled up to voltages as high as 55V when
disabled
,
and can sink currents up to 1mA when enabled
(<0.4V). Pull down currents as high as 5mA (absolute
maximum) are supported for higher current applications,
such as lighting LEDs.
If the LTC4020 is configured for a CC/CV charging algo
-
rithms, the STAT2 pin is pulled low during NTC faults or
after a bad battery fault occurs.
If the LTC4020 is configured for a CC charging algorithms,
the STAT2 pin is pulled low during NTC faults.
If the LTC4020 is configured for a lead-acid charging
algorithm, the STAT2 pin is used as a charge cycle stage
indicator pin, and pulled low during the bulk and float
charging stages. The pin is high impedance during the
absorption charging stage and during NTC or bad bat
-
tery faults.
See Applications Information section.
TIMER (Pin 14): End-Of-Cycle Timer Programming Pin.
If a timer based charging algorithm is desired, connect
a capacitor (C
TIMER
) from this pin to ground. If no timer
functions are desired, connect this pin to ground.
End-of-cycle time (in hours) is programmed with the value
of C
TIMER
following the equation:
T
EOC
= C
TIMER
• 1.46 x 10
7
;
During CC/CV or lead-acid charging algorithms, a bad bat-
tery fault is generated if the battery voltage does not reach
the precondition threshold voltage within 1/8
of T
EOC
, or:
T
PRE
= C
TIMER
• 1.82 x 10
6
.
A 0.2µF capacitor is typically used for CC/CV charging,
which generates a 2.9 hour timer T
EOC
, and a precondition
limit time of 22 minutes. A 0.47µF capacitor is typically
used for a lead-acid charger, which generates a 6.8 hour
absorption stage safety timeout.
RNG/SS (Pin 15): Battery Charge Current Programming
Pin. This pin allows dynamic adjustment of maximum
charge current, and can be used to employ a soft-start
function.
Setting the voltage on the RNG/SS pin reduces maximum
charge current from the value programmed. The maximum
charge current is reduced to the fraction of programmed
current (as per the sense resistor, RCS) corresponding
to the voltage set on the pin (in volts). This pin has an
effective range from 0 to 1V.
For example, with 0.5V RNG/SS on the pin, the maximum
charge current will be reduced to 50% of the programmed
value set by the sense resistor values.
50µA is sourced from the RNG/SS pin, so maximum
charge current can be programmed by connecting a single
resistor (R
RNG/SS
) from RNG/SS to ground, such that the
voltage dropped across the resistor is equivalent to the
desired pin voltage:
V
RNG/SS
= 50µA • R
RNG/SS
Soft-start functionality can be implemented by connecting
a capacitor (C
RNG/SS
) from RNG/SS to ground, such that
the time required to charge the capacitor is the desired
soft-start interval (T
SS1
). The voltage that corresponds to
full programmed inductor current on the RNG/SS pin is
1V, so the relation for this capacitor reduces to:
C
RNG/SS
= 50µA • T
SS1
pin FuncTions
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