Datasheet LT1571 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | Constant-Current/Constant-Voltage Battery Charger with Preset Voltage and Termination Flag |
| Pages / Page | 16 / 10 — APPLICATIO S I FOR ATIO. Lithium-Ion Charging. Charge Termination Flag … |
| File Format / Size | PDF / 220 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Lithium-Ion Charging. Charge Termination Flag Threshold Setting. Lithium-Ion Charge Completion
Model Line for this Datasheet
Text Version of Document
LT1571 Series
U U W U APPLICATIO S I FOR ATIO Lithium-Ion Charging
CAP pin to filter out the switching noise and a pull-up The circuit in Figure 4 uses the 28-pin LT1571-2 to charge resistor is also needed at FLAG pin. lithium-ion batteries at a constant 1A until the battery
Charge Termination Flag Threshold Setting
voltage reaches 8.4V preset battery voltage. The charger will then automatically go into a constant-voltage mode The charge termination flag threshold can be reduced with current decreasing to near zero over time as the from the default 20% level to as low as 7.5% of the battery reaches full charge. programmed full charge current. This is done by adding a resistor RCAP from the CAP pin to ground (see Figure 5).
Lithium-Ion Charge Completion
The formula for selecting the RCAP resistor is: Some battery manufacturers recommend termination of constant-voltage float mode after charge current has R Threshold PROG = 0 2 . 0 – 1 ( 331 . ) dropped below a specified level (typically around 10% to RCAP 20% of the full current) and a further time-out period of 30 or minutes to 90 minutes has elapsed. Check with manufac- 1 ( 331 . )RPROG turer for details. The LT1571 provides a signal at the FLAG RCAP = pin when the charger is in voltage mode and charge 0 2 . 0 – Threshold current has reduced to approximately 20% of full current. R Note that full current is (2.465V × 2000)/R PROG is the charge current setting resistor. PROG. Compara- tor E6 in the Block Diagram compares the charge current LT1571 sample IPROG to the output current IVA voltage amplifier VA. When the charge current drops to 20% of full current, CAP IPROG will be equal to 0.25 IVA and the open-collector R 0.1µF CAP output VFLAG will go low. This signal can be used to start an external timer or to terminate the charge. When this 1571 F05 feature is used, a capacitor of at least 0.1µF is required at
Figure 5. Reducing Charge Termination Threshold
D3 D1 MBRM120T3 MBRM120T3 VIN SW VCC 11V CIN* TO 26V C1 LT1571-2 0.22µF 10µF L1** BOOST PROG 33µH D2 1µF 0.3 4.93k µF 100k MMBD914L SENSE VC 300Ω 1k CAP 0.1µF FLAG SELECT BAT + C + OUT GND BAT2 22µF 8.4V TANT NOTE: COMPLETE LITHIUM-ION CHARGER TOKIN OR MARCON CERAMIC SURFACE MOUNT * 1571 F04 COILTRONICS CTX33-2 **
Figure 4. 200kHz Charging Lithium Batteries (Efficiency at 1A > 87%)
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U U W U APPLICATIO S I FOR ATIO Lithium-Ion Charging
CAP pin to filter out the switching noise and a pull-up The circuit in Figure 4 uses the 28-pin LT1571-2 to charge resistor is also needed at FLAG pin. lithium-ion batteries at a constant 1A until the battery
Charge Termination Flag Threshold Setting
voltage reaches 8.4V preset battery voltage. The charger will then automatically go into a constant-voltage mode The charge termination flag threshold can be reduced with current decreasing to near zero over time as the from the default 20% level to as low as 7.5% of the battery reaches full charge. programmed full charge current. This is done by adding a resistor RCAP from the CAP pin to ground (see Figure 5).
Lithium-Ion Charge Completion
The formula for selecting the RCAP resistor is: Some battery manufacturers recommend termination of constant-voltage float mode after charge current has R Threshold PROG = 0 2 . 0 – 1 ( 331 . ) dropped below a specified level (typically around 10% to RCAP 20% of the full current) and a further time-out period of 30 or minutes to 90 minutes has elapsed. Check with manufac- 1 ( 331 . )RPROG turer for details. The LT1571 provides a signal at the FLAG RCAP = pin when the charger is in voltage mode and charge 0 2 . 0 – Threshold current has reduced to approximately 20% of full current. R Note that full current is (2.465V × 2000)/R PROG is the charge current setting resistor. PROG. Compara- tor E6 in the Block Diagram compares the charge current LT1571 sample IPROG to the output current IVA voltage amplifier VA. When the charge current drops to 20% of full current, CAP IPROG will be equal to 0.25 IVA and the open-collector R 0.1µF CAP output VFLAG will go low. This signal can be used to start an external timer or to terminate the charge. When this 1571 F05 feature is used, a capacitor of at least 0.1µF is required at
Figure 5. Reducing Charge Termination Threshold
D3 D1 MBRM120T3 MBRM120T3 VIN SW VCC 11V CIN* TO 26V C1 LT1571-2 0.22µF 10µF L1** BOOST PROG 33µH D2 1µF 0.3 4.93k µF 100k MMBD914L SENSE VC 300Ω 1k CAP 0.1µF FLAG SELECT BAT + C + OUT GND BAT2 22µF 8.4V TANT NOTE: COMPLETE LITHIUM-ION CHARGER TOKIN OR MARCON CERAMIC SURFACE MOUNT * 1571 F04 COILTRONICS CTX33-2 **
Figure 4. 200kHz Charging Lithium Batteries (Efficiency at 1A > 87%)
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