lt3652hv Linear Technology Corporation, lt3652hv Datasheet - Page 10

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

LT3652HV
APPLICATIONS INFORMATION
Overview
LT3652HV is a complete monolithic, mid-power, multi-
chemistry buck battery charger, addressing high input
voltage applications with solutions that require a minimum
of external components. The IC uses a 1MHz constant fre-
quency, average-current mode step-down architecture.
The LT3652HV incorporates a 2A switch that is driven
by a bootstrapped supply to maximize efficiency during
charging cycles. Wide input range allows operation to full
charge from voltages as high as 34V. A precision threshold
shutdown pin allows incorporation of UVLO functionality
using a simple resistor divider. The IC can also be put into
a low-current shutdown mode, in which the input supply
bias is reduced to only 15μA.
The LT3652HV employs an input voltage regulation loop,
which reduces charge current if a monitored input voltage
falls below a programmed level. When the LT3652HV is
powered by a solar panel, the input regulation loop is used
to maintain the panel at peak output power.
The LT3652HV automatically enters a battery precondition
mode if the sensed battery voltage is very low. In this mode,
the charge current is reduced to 15% of the programmed
maximum, as set by the inductor sense resistor, R
Once the battery voltage reaches 70% of the fully charged
float voltage, the IC automatically increases maximum
charge current to the full programmed value.
The LT3652HV can use a charge-current based C/10
termination scheme, which ends a charge cycle when
the battery charge current falls to one tenth of the pro-
grammed maximum charge current. The LT3652HV also
contains an internal charge cycle control timer, for timer-
based termination. When using the internal timer, the
IC combines C/10 detection with a programmable time
constraint, during which the charging cycle can continue
beyond the C/10 level to top-off a battery. The charge
cycle terminates when a specific time elapses, typically 3
hours. When the timer-based scheme is used, the IC also
supports bad battery detection, which triggers a system
fault if a battery stays in precondition mode for more than
one eighth of the total charge cycle time.
Once charging is terminated, the LT3652HV automati-
cally enters a low-current standby mode where supply
bias currents are reduced to 85μA. The IC continues to
10
SENSE
.
monitor the battery voltage while in standby, and if that
voltage falls 2.5% from the full-charge float voltage, the
LT3652HV engages an automatic charge cycle restart. The
IC also automatically restarts a new charge cycle after a
bad battery fault once the failed battery is removed and
replaced with another battery.
The LT3652HV contains provisions for a battery tem-
perature monitoring circuit. This feature monitors battery
temperature using a thermistor during the charging cycle.
If the battery temperature moves outside a safe charg-
ing range of 0°C to 40°C, the IC suspends charging and
signals a fault condition until the temperature returns to
the safe charging range.
The LT3652HV contains two digital open-collector outputs,
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.
General Operation (See Block Diagram)
The LT3652HV uses average current mode control loop
architecture, such that the IC servos directly to average
charge current. The LT3652HV senses charger output
voltage through a resistor divider via the V
difference between the voltage on this pin and an internal
3.3V voltage reference is integrated by the voltage error
amplifier (V-EA). This amplifier generates an error volt-
age on its output (I
current sensed across the inductor current sense resistor,
R
pins. The I
10, and imposed on the input of the current error amplifier
(C-EA). The difference between this imposed voltage and
the current sense resistor voltage is integrated, with the
resulting voltage (V
against an internally generated ramp. The output of this
comparison controls the charger’s switch.
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-
SENSE
TH
, which is connected between the SENSE and BAT
error voltage corresponds linearly to average
TH
voltage is then divided down by a factor of
TH
C
) used as a threshold that is compared
), which corresponds to the average
TH
. A clamp limits this voltage
FB
pin. The
3652hvf