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DEMO CIRCUI
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1568
DESCRIPTION
Demonstration Circuit 1568A is a 2A Monolithic
Multi-Chemistry battery charger for solar power
applications featuring the LT3652EDD. The
LT3652 is a complete mid-power Li-Ion battery
charger that can operate over a wide input voltage range. The charger employs a 3.3V float
voltage feedback reference that allows the battery float voltage to be adjusted up to 14.4V.
R10 and R11, in the demonstration circuit, set
the float voltage and are 0603 resistors to accommodate the use of 0.1% resistors if desired.
The circuit is constructed with 1% resistors
which could introduce as much as a 1.56% error
in the float voltage. Replacing these resistors
with 0.1% resistors would introduce less than a
0.154% error. The LT3652 has an input voltage
regulation loop which reduces charge current if
QUICK START GUID
LT3652EDD
LT3652ED
2A Monolithic Multi
Chemistry Battery Charge
the input falls below a programmed level, set
with a resistor divider. The charger is a CC/CV
charger with a maximum charge current of 2A. A
precondition feature trickle charges a lowvoltage battery, and bad battery detection provides a signal if the battery doesn’t respond to
preconditioning.
The LT3652EDD is available in a 12-lead (3mm
× 3mm) DFN surface mount package with an
exposed pad.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, μModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency ΔΣ, No Latency Delta-Sigma, No R
PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
, Operational Filter, PanelProtect,
SENSE
Table 1: Typical Specifications (25°C)
HV Input Voltage Range 11.5V to 32V
VOUT 8.04V to 8.36V
Output Float Voltage (constant voltage mode) 8.2V
Output Current Limit ILIM 2A
OPERATING PRINCIPLE
LT3652 is a complete monolithic mid-power Li-Ion battery charger, addressing high input voltage applications
with solutions that require a minimum of external components. The IC uses a 1MHz constant frequency, average-current mode step-down architecture.
The LT3652 incorporates a 2A switch that is driven by a
bootstrapped supply to maximize efficiency during
charging cycles. A wide input range allows operation to
fully charge from 11.5V (single cell) to 32V. A precisionthreshold shutdown pin allows the 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 15uA.
The LT3652 incorporates several degrees of charge current control freedom. The overall maximum charge cur-
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LT3652EDD
rent is set using an external inductor current sense resistor. A maximum charge current programming pin allows
dynamic manipulation of the battery charge current. The
LT3650 also incorporates a system input-supply current
limit control feature that servos the battery charge current to accommodate overall system load requirements.
The LT3652 automatically enters a battery precondition
mode if the sensed battery voltage is very low. In this
mode, the charging current is reduced to 15% of the
programmed maximum, as set by the inductor sense
resistor, R
internally set threshold of 5.7V / cell, the IC automatically
increases maximum charging current to the full programmed value.
The LT3652 can use a charge-current based ‘C/10’ termination scheme, which ends a charge cycle when the
battery charge current falls to 1/10th the programmed
maximum charge current. The LT3652 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
. Once the battery voltage climbs above an
SENSE
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 1/8th of the total charge cycle time.
Once charging is terminated and the LT3652 is not actively charging, the IC automatically enters a low-current
standby mode where supply bias currents are reduced to
< 100uA. If the battery voltage drops 2.5% from the fullcharge float voltage, the LT3652 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 LT3652 includes provisions for a battery temperature monitoring circuit. This feature monitors battery
temperature during the charging cycle using a thermistor, and suspends charging and signals a fault condition
if the battery temperature moves outside a safe charging
range of 0OC to 50OC.
The LT3652 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.
QUICK START PROCEDURE
Demonstration circuit 1568A is easy to set up to evaluate
the performance of the LT3652EDD.
Using short twisted pair leads for any power connections, with all loads and power supplies off, refer to
Figure 1 for the proper measurement and equipment
setup.
Follow the procedure below:
1. Jumper and Power Supply Setting:
JP1 = 1 JP4 = 1
JP2 = 1 PS1 = OFF
JP3 = C/10 PS2 = OFF
2. Turn on PS2 and slowly increase the voltage to
5.4V while monitoring the current into the BAT
pin. If the current is less than 5mA, turn on PS1.
Increase the voltage on PS1 to 5V while monitoring the input current. If the current is less than
5mA, increase PS1 to 12V.
3. Verify that the battery charging current, IBAT, is
between 250mA and 350mA. The CHRG LED
should be on and the FAULT LED should be off.
4. Increase PS2 until VBAT is 7.2V. Verify the input
current, IIN, is between 1.3A and 1.7A, the battery
current, IBAT, is between 1.775A and 2.225A and
that the CHRG LED is on.
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LT3652EDD
5. Increase PS2 until VBAT is 8.5V. Verify the battery
charging current, IBAT, is less than 5mA and that
the CHRG
6. Decrease PS2 until VBAT is 7.8V. Verify the battery current, IBAT, is between 1.775A and 2.225A
and that the CHRG LED is on.
7. Set JP1 to 0. Verify the charging current, IBAT, is
less than 5mA and that the FAULT LED and the
CHRG LED are off.
8. Set JP1 to 1. Connect a jumper from the NTC pin
to ground. Verify the charging current, IBAT, is
less than 5mA and that the FAULT LED and the
CHRG LED are on.
9. Remove the jumper from NTC to ground. Verify
the charging current, IBAT, is between 1.775A and
2.225A and that the FAULT LED is off and the
CHRG LED is on.
LED is off.
10. Turn on LOAD1 and set to 1A. Verify the voltage,
Vsystem, on the System Load turret is approximately equal to Vin.
11. Set JP2 to 0. Verify the battery charging current is
less than 5mA and that the CHRG LED is off.
12. Increase PS1 to 14V. Verify the charging current
is between 1.775A and 2.225A and that the CHRG
LED is on. Set JP2 to 1.
13. Set JP4 to 0. Verify the battery charging current is
less than 5mA and that the CHRG LED is off.
14. Increase PS1 to 17.7V. Verify the charging current
is between 1.775A and 2.225A and that the CHRG
LED is on. Set JP4 to 1.
15. Turn off PS1, PS2 and LOAD1.
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LT3652EDD
Note: All connections from equipment should be Kelvin connected directly to the Board PINS which they are
connected to on this diagram and any input, or output, leads should be twisted pair.
Figure 1. Proper Measurement Equipment Setup for DC1568A
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LT3652EDD
Figure 2: Schematic diagram
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LT3652EDD
Bill of Materials
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