LT3652 LINER [Linear Technology], LT3652 Datasheet - Page 11

• Manufacturer Part Number: LT3652
• Description: Power Tracking 2A Battery Charger for Solar Power
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
The I
current sensed across the inductor current sense resistor,
allowing maximum charge current control by limiting the
effective voltage range of I
to 1V which, in turn, limits the current sense voltage to
100mV. This sets the maximum charge current, or the
current delivered while the charger is operating in con-
stant-current (CC) mode, which corresponds to 100mV
across R
this maximum charge current should the voltage on the
V
perature approaches 125°C.
If the voltage on the V
the LT3652 engages precondition mode. During the
precondition interval, the charger continues to operate in
constant-current mode, but the maximum charge current
is reduced to 15% of the maximum programmed value
as set by R
When the charger output voltage approaches the float volt-
age, or the voltage on the V
the charger transitions into constant-voltage (CV) mode
and charge current is reduced from the maximum value.
As this occurs, the I
and servos to lower voltages. The IC monitors the I
age as it is reduced, and detection of C/10 charge current
is achieved when I
for C/10 termination, this threshold is used to terminate
the charge cycle. Once the charge cycle is terminated,
the CHRG status pin becomes high-impedance and the
charger enters low-current standby mode.
The LT3652 contains an internal charge cycle timer that
terminates a successful charge cycle after a programmed
amount of time. This timer is typically programmed to
achieve end-of-cycle (EOC) in 3 hours, but can be con-
figured for any amount of time by setting an appropriate
timing capacitor value (C
is used, the charge cycle does not terminate when C/10
is achieved. Because the CHRG status pin responds to
IN_REG
TH
pin falls below 2.7V (V
SENSE
error voltage corresponds linearly to average
SENSE
. The I
.
TH
TH
TH
= 0.1V. If the charger is configured
voltage falls from the limit clamp
FB
voltage is pulled down to reduce
FB
TIMER
TH
pin is below 2.3V (V
pin approaches 3.3V (V
. A clamp limits this voltage
). When timer termination
IN_REG(TH)
) or the die tem-
FB(PRE)
FB(FLT)
TH
volt-
),
),
the C/10 current level, the IC will indicate a fully-charged
battery status, but the charger continues to source low
currents into the battery until the programmed EOC time
has elapsed, at which time the charge cycle will terminate.
At EOC when the charging cycle terminates, if the battery
did not achieve at least 97.5% of the full float voltage,
charging is deemed unsuccessful, the LT3652 re-initiates,
and charging continues for another full timer cycle.
Use of the timer function also enables bad-battery detec-
tion. This fault condition is achieved if the battery does
not respond to preconditioning, such that the charger
remains in (or enters) precondition mode after 1/8th of
the programmed charge cycle time. A bad battery fault
halts the charging cycle, the CHRG status pin goes high-
impedance, and the FAULT pin is pulled low.
When the LT3652 terminates a charging cycle, whether
through C/10 detection or by reaching timer EOC, the
average current mode analog loop remains active, but
the internal float voltage reference is reduced by 2.5%.
Because the voltage on a successfully charged battery is
at the full float voltage, the voltage error amp detects an
over-voltage condition and I
voltage error amp output drops below 0.3V, the IC enters
standby mode, where most of the internal circuitry is dis-
abled, and the V
the voltage on the V
reference level, the output of the voltage error amp will
climb, at which point the IC comes out of standby mode
and a new charging cycle is initiated.
V
The LT3652 is biased directly from the charger input supply
through the V
currents, so a high-quality, low ESR decoupling capacitor
is recommended to minimize voltage glitches on V
V
IN
IN
decoupling capacitor (C
Input Supply
IN
IN
pin. This supply provides large switched
bias current is reduced to 85μA. When
FB
pin drops below the reduced float
VIN
TH
) absorbs all input switching
is pulled low. When the
LT3652
11
IN
. The
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