Datasheet LT1513, LT1513-2 (Analog Devices) - 5

LT1513/LT1513-2
U U U PIN FUNCTIONS VC (Pin 1):
The compensation pin is primarily used for
GND (Pin 4):
The ground pin is common to both control frequency compensation, but it can also be used for soft circuitry and switch current. VC, FB and S/S signals must starting and current limiting. It is the output of the error be Kelvin and connected as close as possible to this pin. amplifier and the input of the current comparator. Peak The TAB of the R package should also be connected to the switch current increases from 0A to 3.6A as the VC voltage power ground. varies from 1V to 1.9V. Current out of the VC pin is about
V
200µA when the pin is externally clamped below the
SW (Pin 5):
The switch pin is the collector of the power switch, carrying up to 3A of current with fast rise and fall internal 1.9V clamp level. Loop frequency compensation times. Keep the traces on this pin as short as possible to is performed with a capacitor or series RC network from minimize radiation and voltage spikes. In particular, the the VC pin directly to the ground pin (avoid ground loops). path in Figure 1 which includes SW to C2, D1, C1 and
FB (Pin 2):
The feedback pin is used for positive output around to the LT1513 ground pin should be as short as voltage sensing. The R1/R2 voltage divider connected to possible to minimize voltage spikes at switch turn-off. FB defines Li-Ion float voltage at full charge, or acts as a
S/S (Pin 6):
This pin can be used for shutdown and/or voltage limiter for NiCd or NiMH applications. FB is the synchronization. It is logic level compatible, but can be inverting input to the voltage error amplifier. Input bias tied to V current is typically 300nA, so divider current is normally IN if desired. It defaults to a high ON state when floated. A logic low state will shut down the charger to a set to 100µA to swamp out any output voltage errors due micropower state. Driving the S/S pin with a continuous to bias current. The noninverting input of this amplifier is logic signal of 600kHz to 800kHz will synchronize switch- tied internally to a 1.245V reference. The grounded end of ing frequency to the external signal. Shutdown is avoided the output voltage divider should be connected directly to in this mode with an internal timer. the LT1513 ground pin (avoid ground loops).
V I IN (Pin 7):
The input supply pin should be bypassed with
FB (Pin 3):
The current feedback pin is used to sense a low ESR capacitor located right next to the IC chip. The charging current. It is the input to a current sense amplifier grounded end of the capacitor must be connected directly that controls charging current when the battery voltage is to the ground plane to which the TAB is connected. below a programmed limit. During constant-current operation, the LT1513 I
TAB:
The TAB on the surface mount R package is electri- FB pin regulates at – 100mV. Input resistance of this pin is 5kΩ, so filter resistance (R4, cally connected to the ground pin, but a low inductance Figure 1) should be less than 50Ω. The 39Ω, 0.22µF filter connection must be made to both the TAB and the pin for shown in Figure 1 is used to convert the pulsating current proper circuit operation. See suggested PC layout in in the sense resistor to a smooth DC current feedback Figure 4. 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. sn1513 1513fas 5