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LT1513 Datasheet(PDF) 5 Page - Linear Technology |
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LT1513 Datasheet(HTML) 5 Page - Linear Technology |
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5 / 16 page  5 LT1513/LT1513-2 sn1513 1513fas PIN FUNCTIONS VC (Pin 1): The compensation pin is primarily used for frequency compensation, but it can also be used for soft starting and current limiting. It is the output of the error amplifier and the input of the current comparator. Peak switch current increases from 0A to 3.6A as the VC voltage varies from 1V to 1.9V. Current out of the VC pin is about 200 µA when the pin is externally clamped below the internal 1.9V clamp level. Loop frequency compensation is performed with a capacitor or series RC network from the VC pin directly to the ground pin (avoid ground loops). FB (Pin 2): The feedback pin is used for positive output voltage sensing. The R1/R2 voltage divider connected to FB defines Li-Ion float voltage at full charge, or acts as a voltage limiter for NiCd or NiMH applications. FB is the inverting input to the voltage error amplifier. Input bias current is typically 300nA, so divider current is normally set to 100 µA to swamp out any output voltage errors due to bias current. The noninverting input of this amplifier is tied internally to a 1.245V reference. The grounded end of the output voltage divider should be connected directly to the LT1513 ground pin (avoid ground loops). IFB (Pin 3): The current feedback pin is used to sense charging current. It is the input to a current sense amplifier that controls charging current when the battery voltage is below a programmed limit. During constant-current operation, the LT1513 IFB pin regulates at – 100mV. Input resistance of this pin is 5k Ω, so filter resistance (R4, Figure 1) should be less than 50 Ω. The 39Ω, 0.22µF filter shown in Figure 1 is used to convert the pulsating current in the sense resistor to a smooth DC current feedback signal. The LT1513-2 IFB pin regulates at 0mV to provide programmable current limit. The current through R5, Figure 5, is balanced by the current through R4, program- ming the maximum voltage across R3. GND (Pin 4): The ground pin is common to both control circuitry and switch current. VC, FB and S/S signals must be Kelvin and connected as close as possible to this pin. The TAB of the R package should also be connected to the power ground. VSW (Pin 5): The switch pin is the collector of the power switch, carrying up to 3A of current with fast rise and fall times. Keep the traces on this pin as short as possible to minimize radiation and voltage spikes. In particular, the path in Figure 1 which includes SW to C2, D1, C1 and around to the LT1513 ground pin should be as short as possible to minimize voltage spikes at switch turn-off. S/S (Pin 6): This pin can be used for shutdown and/or synchronization. It is logic level compatible, but can be tied to VIN if desired. It defaults to a high ON state when floated. A logic low state will shut down the charger to a micropower state. Driving the S/S pin with a continuous logic signal of 600kHz to 800kHz will synchronize switch- ing frequency to the external signal. Shutdown is avoided in this mode with an internal timer. VIN (Pin 7): The input supply pin should be bypassed with a low ESR capacitor located right next to the IC chip. The grounded end of the capacitor must be connected directly to the ground plane to which the TAB is connected. TAB: The TAB on the surface mount R package is electri- cally connected to the ground pin, but a low inductance connection must be made to both the TAB and the pin for proper circuit operation. See suggested PC layout in Figure 4. |
Similar Part No. - LT1513_15 |
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Similar Description - LT1513_15 |
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