DEMO CIRCUIT 1473A
LT3650EDD-8.4/8.2
QUICK START GUIDE
LT3650EDD-8.4/8.2
2A Monolithic Li-Ion Battery
Charger
DESCRIPTION
Demonstration Circuit 1473A is a 2A Monolithic Li-Ion
Battery Charger featuring the LT3650EDD-8.4/8.2. The
LT3650 is a complete mid-power Li-Ion battery
charger that can operate over a wide input voltage
range. The charger is a CC/CV charger with a maxi-
mum charge current externally programmable up to
2A. A precondition feature trickle charges a low-
voltage battery and bad battery detection provides a
signal if the battery doesn’t respond to precondition-
ing. The LT3650EDD-8.4/8.2 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
SENSE
, Operational Filter, PanelProtect,
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.
Table 1: Typical Specifications (25°C)
HV Input Voltage Range
VOUT
Output Float Voltage (constant voltage mode)
Output Current Limit ILIM
9V to 32V
7.4V to 8.48V
8.4V/8.2V
2A (R
RNG
equals 20kΩ)
OPERATING PRINCIPLE
LT3650 is a complete monolithic mid-power Li-Ion bat-
tery charger, addressing high input voltage applications
with solutions that require a minimum of external com-
ponents. The IC uses a 1MHz constant frequency, aver-
age-current mode step-down architecture.
The LT3650 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 10V +/- 5% (single cell) to 32V. A pre-
cision-threshold 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 LT3650 incorporates several degrees of charge cur-
rent control freedom. The overall maximum charge cur-
rent is set using an external inductor current sense resis-
tor. 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 cur-
rent to accommodate overall system load requirements.
The LT3650 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
SENSE
. Once the battery voltage climbs above an
internally set threshold of 5.7V / cell, the IC automatically
1
LT3650EDD-8.4/8.2
increases maximum charging current to the full pro-
grammed value.
The LT3650 can use a charge-current based ‘C/10’ ter-
mination scheme, which ends a charge cycle when the
battery charge current falls to 1/10
th
the programmed
maximum charge current. The LT3650 also contains an
internal charge cycle control timer, for timer-based ter-
mination. When using the internal timer, the IC com-
bines C/10 detection with a programmable time con-
straint, 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 1/8
th
of the total charge cycle time.
Once charging is terminated and the LT3650 is not ac-
tively 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 full-
charge float voltage, the LT3650 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 LT3650 includes provisions for a battery tempera-
ture monitoring circuit. This feature monitors battery
temperature during the charging cycle using a thermis-
tor, and suspends charging and signals a fault condition
if the battery temperature moves outside a safe charging
range of 0
O
C to 50
O
C.
The LT3650 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 1473A is easy to set up to evaluate
the performance of the LT3650EDD-8.4/8.2.
Using short twisted pair leads for any power connec-
tions, 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
JP2 = 1
JP3=C/10
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 monitor-
ing the input current. If the current is less than
5mA, increase PS1 to 12V.
PS1 = OFF
PS2 = OFF
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.
5. Increase PS2 until VBAT is 8.5V. Verify the battery
charging current, IBAT, is less than 5mA and that
the CHRG LED is off.
6. Decrease PS2 until VBAT is 7.8V. Verify the bat-
tery current, IBAT, is between 1.775A and 2.225A
that the CHRG LED is on.
7. Decrease PS2 until VBAT is 7.2V. Connect a 10K
resistor from the RNG/SS pin to ground. Verify the
charging current, IBAT, is between 850mA and
1.1A. Verify the voltage, VNTC, on the NTC turret
is between 450mV and 550mV and the voltage,
2
LT3650EDD-8.4/8.2
VRNG, on the RNG/SS turret is between 1.8V and
1.9V. Remove the 10K resistor from the RNG/SS
pin to ground.
8. Set JP1 to 0. Verify the charging current, IBAT, is
less than 5mA and that the FAULT LED and the
CHRG LED are off.
9. 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.
10. 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.
11. Turn on LOAD1 and set to 1A. Verify the voltage,
Vsystem, on the System Load turret is approxi-
mately equal to Vin.
12. Turn off PS1, PS2 and LOAD1.
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
3
LT3650EDD-8.4/8.2
Figure 2: Schematic diagram
4
LT3650EDD-8.4/8.2
Bill of Materials
5
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