lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 11

• Manufacturer Part Number: lt3652hv
• Description: Lt3652hv Power Tracking 2a Battery Charger Features
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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 LT3652HV 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 LT3652HV 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
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 LT3652HV 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
IN_REG
pin falls below 2.7V (V
SENSE
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
pin is below 2.3V (V
pin approaches 3.3V (V
). When timer termination
IN_REG(TH)
) or the die tem-
FB(PRE)
FB(FLT)
TH
volt-
),
),
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 LT3652HV 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 LT3652HV is biased through a reverse-current block-
ing element from the charger input supply to the V
This supply provides large switched currents, so a high-
quality, low ESR decoupling capacitor is recommended
to minimize voltage glitches on V
capacitor (C
in the charger, so it must have an adequate ripple current
rating. RMS ripple current (I
where I
(100mV/R
V
The simple worst-case of ½ • I
used for design.
IN
IN
I
I
CVIN(RMS)
CVIN(RMS)
Input Supply
= 2 • V
CHG(MAX)
SENSE
BAT
VIN
≅ I
, where:
= I
) absorbs all input switching ripple current
CHG(MAX)
IN
). The above relation has a maximum at
CHG(MAX)
is the maximum average charge current
bias current is reduced to 85μA. When
FB
pin drops below the reduced float
• (V
/2.
BAT
CVIN(RMS)
TH
/ V
is pulled low. When the
IN
CHG(MAX)
IN
)•([V
. The V
LT3652HV
) is:
IN
/ V
IN
is commonly
BAT
decoupling
] – 1)
11
IN
1/2
3652hvf
pin.
,