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2.1.2

Li-Ion

Set To:

SEL1

SEL2

SEL3

V

CC

After charging, maintenance charging until battery removal.

NA

4.2V/Cell

Hi-Z

After charging, maintenance charging until battery removal. If battery
voltage drops below a predefined value, the charger restarts the
charge-process.

Li-Ion

NA

GND

After charging, no maintenance charging is applied. If battery voltage
drops below a predefined value, the charger restarts the charge-process.

NA

4.1V/Cell

Note: When a three chemistry charger is designed, special considerations must be taken into account regarding configuration pin SEL3. this pin has differnet

meanings when switching between Ni-Cd/Ni-MH and Li-Ion. To ensure correct operation, the SEL3-pin MUST be tied to VCC. If Li-Ion cells of 4.1V/Cells is
used, then minor adjustments have to be done to the voltage measurement resistor divider.

AN101315-9

AN-1

164

www.national.com

7

Summary of Contents for LM3647

Page 1: ...N INFORMATION The following documentation describes how to use the LM3647 demo board and also gives a few tips on design calculations Please note that not all components on the demo board are used when designing a charger application The demo board has extra components to make it simple for the user to try out different batteries and configurations There are actually two different charge current r...

Page 2: ...in range to start charging If it is then it applies a small current of 0 2C for approximately 5 minutes If the battery voltage exceeds the maximum battery voltage CEL pin 3 017V the LM3647 stops charging and stays in error mode until the battery is removed If the battery voltage has not risen above the bad battery threshold CEL pin 1 2V then the battery is considered to be defective and the charge...

Page 3: ...output and have a high PSRR PowerSup plyRejectionRatio because they are both powered directly from the unregulated DC input U1 must also have enough current drive to control the transistor Q3 U2 should preferably have a low input offset since this error will be amplified The regulator IC2 criteria is that it has to be able to handle the input DC voltage and deliver enough current to drive the circ...

Page 4: ...operational amplifier and fed to the CS pin on the LM3647 The gain must be dimensioned by setting the appropriate ratio between R1 R2 and R3 R4 The figure below is dimensioned for a maximum current of about 1 1A This was dimensioned using the following formula 1 2 2 5 Setting Maximum Battery Voltage The resistor network see the figure below scales the battery voltage to a suitable level for the LM...

Page 5: ...EL3 can also be used if there is problem in finding the right values in the resistor network The recommended tolerance of the resistors are 0 1 but 1 may be used with a marginal loss of battery capacity by subtracting the tolerance of the divider network from the maximum battery voltage Using the LM3647 without current feedback for Ni Cd Ni MH only slow PWM mode This mode uses an external constant...

Page 6: ...1 1 Ni Cd Ni MH Set To SEL1 SEL2 SEL3 VCC No Discharge before Charge Ni MH Fast PWM LM3647 has current feedback Hi Z Discharge before Charge NA NA GND Maintenance Charge Only Ni Cd Slow PWM external current control AN101315 8 AN 1164 www national com 6 ...

Page 7: ...f battery voltage drops below a predefined value the charger restarts the charge process NA 4 1V Cell Note When a three chemistry charger is designed special considerations must be taken into account regarding configuration pin SEL3 this pin has differnet meanings when switching between Ni Cd Ni MH and Li Ion To ensure correct operation the SEL3 pin MUST be tied to VCC If Li Ion cells of 4 1V Cell...

Page 8: ...gnal The jumper with the battery voltage ranges are shown below The I jumper J10 is used to select between different current sense resistors The values mounted are 0 047Ω and 0 100Ω The different current sense voltage amplification level is selected via CURRENT jumpers J9 and J13 both jumpers must be changed in pairs see figure below The upper values correspond to a current sense resistor of 0 047...

Page 9: ...n be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor Corporation Americas Tel 1 800 272 9959 Fax 1 800 737 7018 Email support nsc com National Semiconductor Europe Fax 49 0 180 530 85 86 Email europe support nsc com Deutsch Tel 49 0 69 9508 6208 English Tel 44 0 870 24 0 2171 Français Tel 33 0 1 41 91 879...

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