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LT1510CS8 Datasheet(PDF) 11 Page - Linear Technology |
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LT1510CS8 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 16 page  11 LT1510/LT1510-5 APPLICATIONS INFORMATION period, after which the LT1510 can be shut down by pulling the VC pin low with an open collector or drain. Some external means must be used to detect the need for additional charging if needed, or the charger may be turned on periodically to complete a short float-voltage cycle. Current trip level is determined by the battery voltage, R1 through R3, and the internal LT1510 sense resistor ( ≈ 0.18Ω pin-to-pin). D2 generates hysteresis in the trip level to avoid multiple comparator transitions. Nickel-Cadmium and Nickel-Metal-Hydride Charging The circuit in Figure 6 uses the 8-pin LT1510 to charge NiCd or NiMH batteries up to 12V with charging currents of 0.5A when Q1 is on and 50mA when Q1 is off. of the battery, canceling part or all of the 200 µA. Note that if net current is into the battery and the battery is removed, the charger output voltage will float high, to near input voltage. This could be a problem when reinserting the battery, if the resulting output capacitor/battery surge current is high enough to damage either the battery or the capacitor. If net current into the battery must be less than zero in shutdown, there are several options. Increasing divider current to 300 µA - 400µA will ensure that net battery current is less than zero. For long term storage conditions however, the divider may need to be disconnected with a MOSFET switch as shown in Figures 2 and 5. A second option is to connect a 1N914 diode in series with the MOSFET drain. This will limit how far the VC pin will be pulled down, and current ( ≈ 700µA) will flow into the BAT pin, and therefore out of the battery. This is not usually a problem unless the charger will remain in the shutdown state with input power applied for very long periods of time. Removing input power to the charger will cause the BAT pin current to drop to near zero, with only the divider current remaining as a small drain on the battery. Even that current can be eliminated with a switch as shown in Figures 2 and 5. Figure 5. Disconnecting Voltage Divider Some battery manufacturers recommend termination of constant-voltage float mode after charging current has dropped below a specified level (typically 50mA to 100mA) and a further time-out period of 30 minutes to 90 minutes has elapsed. This may extend the life of the battery, so check with manufacturers for details. The circuit in Figure 7 will detect when charging current has dropped below 75mA. This logic signal is used to initiate a time-out Figure 6. Charging NiMH or NiCd Batteries (Efficiency at 0.5A ≈ 90%) For a 2-level charger, R1 and R2 are found from: I R BAT PROG = ()( ) 2000 2 465 . R I R II LOW HI LOW 1 2 465 2000 2 2 465 2000 = ()( ) = ()( ) − .. All battery chargers with fast-charge rates require some means to detect full charge state in the battery to terminate the high charging current. NiCd batteries are typically charged at high current until temperature rise or battery R3 12k R4 4.99k 0.25% R5 220k OVP VIN + – + – 4.2V 4.2V VBAT Q3 VN2222 LT1510 1510 F05 SW BOOST GND SENSE VCC PROG VC BAT R2 11k + R1 100k Q1 VN2222 * TOKIN OR MARCON CERAMIC SURFACE MOUNT ** COILTRONICS CTX33-2 WALL ADAPTER 1510 F05.5 C1 0.22 µF CIN* 10 µF L1** 33 µH LT1510 D1 1N5819 D3 1N5819 D2 1N914 + COUT 22 µF TANT 0.1 µF + 1k 1 µF 300 Ω 2V TO 20V IBAT ON: IBAT = 0.5A OFF: IBAT = 0.05A |
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Similar Description - LT1510CS8 |
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