Quick Start Manual For Linear Technology
Demo board DC370A-A (4.1V) and DC370A-B (4.2V)
LTC1734 Linear Battery Charger for One Li-Ion Cell at 4.1V or 4.2V
Demonstration board DC370A is a constant-current/constant-
voltage battery charger designed to charge one Lithium-Ion cell. This
demoboard features a preset charge voltage (±1%) where the charge
current can be easily programmed and monitored allowing for easy
interface with a CPU or other circuitry providing charge termination.
The LTC1734 used on this demoboard drives an inexpensive PNP
transistor in a linear regulator configuration that provides up to
700mA of charge current. The IC and the pass transistor are
available in tiny 5 and 6-pin SOT 23 packages which reduces the
total circuit area to less than 0.08 square inches, although additional
pc-board copper area is needed for heat dissipation.
Other Features include; Preset float voltages of 4.1 & 4.2V ±1%
700mA Constant Current (can be programmed for other charge
currents ranging from 100mA to 700mA)
Monitor charge current using the Program pin
No isolation diode required
No sense resistor required
Manual Shutdown
Low battery drain current when input supply is removed
Typical Demo Board Specifications
Input Voltage Range (VIN ) 4.7V to 7V (upper range limited by pc board
dissipation) Output Voltage (VBAT ) in constant voltage
mode 4.1 ±1% for DC370A-A and 4.2V ±1% for
DC370A-B Output Current (IBAT ) in constant
current mode 700mA ±10%
Program pin voltage at full charge current
1.5V ± 5% Battery
Drain Current with VIN Removed <1µA
Test Equipment Required for Demo Board Evaluation
Lab Power supply for input power 0 to 7V @ 1A
Digital voltmeter for measuring input voltage (VIN) 3-1/2 digits
Digital voltmeter for measuring battery voltage (VBAT) 4-1/2 digits, resolution to 1mV
Digital voltmeter for measuring program pin voltage 3-1/2 digits, resolution to 1mV
Digital voltmeter for measuring voltage across 3-1/2 digits
current sense resistor
Li-Ion cell or *Battery Simulator 4.1 or 4.2V Rechargeable Li-Ion
Cell
*Battery Simulator consists of;
Power supply with coarse and fine 0 to 5V @2A
output voltage adjust controls
1
Power resistor (preload for power supply) 2Ω 10W
Current sense resistor for measuring charge current (IBAT)
0.1Ω 1% 1W
Current sense resistor for measuring battery drain current
1kΩ 1% .5W
Demoboard Evaluation
Begin by assuring that the SHDN jumper (JP1) near the bottom of the demo board is installed.
Referring to the setup diagram, connect the input power supply to the +VIN and Ground pins of
the demo board (power supply set for 0V). Connect the battery simulator (power supply also set
to 0V) to the BATT and GND pins, with the 0.1Ω current sense resistor in the charge path as
shown in the setup diagram. The battery simulator consists of an adjustable power supply and a
2 ohm 10 Watt resistor load in parallel with the power supply output. Connect the digital
voltmeters to measure charger input voltage VIN, charger voltage VBAT, program pin voltage
VPROG, and charge current IBAT.
Undervoltage Lockout - Start the demoboard evaluation by increasing the input power supply to
approximately 4.0V (battery simulator power supply set for 0V). The charger output voltage and
charge current should be 0. The charger is off due to the undervoltage lockout feature.
Constant Current - Set the battery simulator power supply (VBAT) to approximately 2.6V, and
the input power supply to approximately 5.0V. The constant current portion of the charge cycle
will immediately begin resulting in approximately 700mA of current flowing into the battery
simulator, indicated by a reading of 70mV on the charge current DVM. This is the constant
current portion of the charge cycle.
VPROG Verification - With the 700mA charge current flowing into the battery simulator, measure
the program pin voltage VPROG. This voltage is proportional to charge current with 1.5V
indicating full programmed current.
2
Constant Voltage - Begin increasing the battery simulator power supply, thus simulating a
battery accepting charge. The charge current will remain at the programmed value of 700mA
until the charger output voltage is within approximately 10mV of the of the preset charge
voltage, at which time the charge current will begin to decrease. This is the beginning of the
constant Voltage portion of the charge cycle.
Demoboard Test Setup Diagram
Input
Power
Supply
0 to 6V
@1A
5V
+
-
Battery
Simulator
Bench Power
Supply
0V to 4.3V
@2.5A
+
-Course Fine
Voltage Adjust
Volt
Meter
Volt
Meter
Measure Charge Current (IBAT)
2 Ohm
10W
Preload
Li-Ion Battery Simulator
Measure Charge Voltage (VBAT)
0.1ž
1%
Note: Do not
exceed 6V.
Volt
Meter
Measure Input Voltage
+VIN
GND
BAT
GND
LTC1734ES6
Demo DC370A-A or B
(408)432-1900
TECHNOLOGY
PROG Volt
Meter
Montor Program Pin Voltage (VPROG)
3
4
Continue slowly increasing the battery simulator power supply until the charge current drops to
approximately 70mA (7mV on the charge current DVM), then read the charger output voltage on
the DVM. This reading is the charger float voltage which will be either 4.1V or 4.2V ± 40mV
depending on which version of the demoboard is being evaluated. The program pin voltage will
indicate approximately 150mV, indicating 10% of the full programmed current.
Shutdown - Remove the SHDN jumper JP1. The charger will shut down dropping the charge
current to 0mA. Quiescent current from the input supply will remain. Replace the jumper.
Sleep Mode - with input power removed, the LTC1734 enters a sleep mode dropping the battery
drain current to near 0µA. To verify battery drain current, remove the input supply voltage or
shut the supply off, replace the 0.1Ω current sense resistor with a 1kΩ, and set the battery
simulator power supply to approximately 4V. The charge current DVM will now read battery
drain current with 1mV/µA.
Note; Athough it would take more time, this charger can also be evaluated using a
rechargeable Li-Ion battery instead of the battery simulator. If an actual battery is
used, keep the DC resistance between the charger and the battery to a
minimum, as this will affect the charge current in the constant voltage mode.
