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LTC1729 Datasheet(PDF) 7 Page - Linear Technology |
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LTC1729 Datasheet(HTML) 7 Page - Linear Technology |
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7 / 16 page  7 LTC1729 Series Overview The LTC1729 is a charge termination controller for the LT1505/LT1510/LT1511/LT1512/LT1513/LT1769 con- stant-voltage/constant-current battery charger family. Table 1 details these chargers. The primary function of this IC is to stop the charger after three hours of constant- voltage/constant-current charging. The secondary func- tion of this controller includes an indication when the charge current (during constant-voltage mode) drops below a user-selected threshold. A 500kHz Li-Ion cell phone charger is shown in Figure 1. The LTC1729 requires only six external components when combined with the standard LT1510 application. The LTC1729 provides a complete and tiny solution for cellular phones and other portable applications. Table 1. Battery Chargers LT1505 4A Step-Down Charger with Input Current Limit LT1510 1.5A Step-Down Charger LT1510-5 1.5A 500kHz Step-Down Charger LT1511 3A Step-Down Charger with Input Current Limit LT1512 2A Switch SEPIC Charger LT1513 3A Switch SEPIC Charger LT1769 2A Step-Down Charger with Input Current Limit Block Diagram Figure 2 shows the block diagram of the LTC1729. The IC consists of six comparators, a resistive divider, a UVLO block and a logic and timer block. 100 µA 50 µA 1729 F03 COMP1 STATUS VCC CHARGE LED LTC1729 SENSE BAT + + – – R2 200 Ω 20mV IBIAS 20mV R1 0.2 Ω CHARGING CURRENT C1 1 µF 3-SEC FILTER LOGIC AND TIMERS Figure 3. C/10 Detection Circuit Comparator COMP1 is used to indicate C/10 charge cur- rent threshold. (“C” is a term used to indicate the Ampere- hour capacity of a cell.) Figure 3 details the C/10 detection circuit. The resistor and capacitor on the SENSE pin filter the signal from the 0.2 Ω current sense resistor R1. The 100 µA current sink on the SENSE pin develops 20mV across the 200 Ω resistor R2. This sets a 20mV offset on COMP1 that sense resistor R1 must equal before C/10 current is indicated. The C/10 is not recognized by the logic until it passes through a 3-second digital filter. For cases where there are multiple batteries to be charged, the LTC1729 detects when a battery is removed and resets the timers for the next charge cycle. The battery present detection is the primary function of comparator COMP2. When the battery is disconnected from the LTC1729, the voltage at the BAT pin will begin ramping upward. This is due to a current source inside the charger or an external pull-up resistor. Once the voltage on the BAT pin exceeds the 4.5V/cell limit, COMP2 signals a VMAX = true to the logic and turns on a transistor that clamps the voltage. There is the possibility of an overvoltage transient at the charging terminals. This occurs if the battery protection circuit, which is often included in the battery pack, opens the connection to the battery during high current charging (constant-current mode). This is a result of energy storage in the inductor. COMP2 senses the overvoltage and clamps the VC pin, reducing the duty cycle of the charger. If the battery protection circuit quickly returns battery connec- tion to the charger (in less than one second), then the LTC1729 continues charging without resetting the timers. APPLICATIO S I FOR ATIO |
Similar Part No. - LTC1729_15 |
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Similar Description - LTC1729_15 |
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