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LTC4002 Datasheet(PDF) 7 Page - Linear Technology |
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LTC4002 Datasheet(HTML) 7 Page - Linear Technology |
7 / 24 page 7 LTC3783 3783f PI FU CTIO S FBN (Pin 1): Error Amplifier Inverting Input/Negative Current Sense Pin. In voltage mode (VFBP ≤ VVREF), this pin senses feedback voltage from either the external resistor divider across VOUT for output voltage regula- tion, or the grounded sense resistor under the load for output current regulation. In constant current/constant voltage mode (VFBP > 2.5V), connect this pin to the negative side of the current-regulating resistor. Nominal voltage for this pin in regulation is either VFBP or (VFBP – 100mV) for VILIM = 1.23V, depending on operational mode (voltage or constant current/constant voltage) set by the voltage at VFBP. FBP (Pin 2): Error Amplifier Noninverting Input/Positive Current Sense Pin. This pin voltage determines the control loop’s feedback mode (voltage or constant current/con- stant voltage), the threshold of which is approximately 2V. In voltage mode (VFBP ≤ VREF), this pin represents the desired voltage which the regulated loop will cause FBN to follow. In constant current/constant voltage mode (VFBP > 2.5V), connect this pin to the positive side of the load current-sensing resistor. The acceptable input ranges for this pin are 0V to 1.23V (voltage mode) and 2.5V to 36V (constant current/constant voltage mode). ILIM(Pin 3): Current Limit Pin. Sets current sense resistor offset voltage (VFBP – VFBN) in constant current mode regulation (i.e., when VFBP > 2.5V). Offset voltage is 100mV when VILIM = 1.23V and decreases proportionally with VILIM. Nominal voltage range for this pin is 0.1V to 1.23V. VREF (Pin 4): Reference Voltage Pin. Provides a buffered version of the internal bandgap voltage, which can be connected to FBP either directly or with attenuation. Nominal voltage for this pin is 1.23V. This pin should never be bypassed by a capacitor to GND. Instead, a 10k resistor to GND should be used to lower pin impedance in noisy systems. FREQ (Pin 5): A resistor from the FREQ pin to ground programs the operating frequency of the chip. The nomi- nal voltage at the FREQ pin is 0.615V. SYNC (Pin 6): This input allows for synchronizing the operating frequency to an external clock and has an internal 100k pull-down resistor. PWMIN (Pin 7): PWM Gate Driver Input. Internal 100k pull-up resistor. While PWMIN is low, PWMOUT is low, GATE stops switching and the external ITH network is disconnected, saving the ITH state. PWMOUT (Pin 8): PWM Gate Driver Output. Used for constant current dimming (LED load) or for output discon- nect (step-up power supply). GATE (Pin 9): Main Gate Driver Output for the Boost Converter. INTVCC (Pin 10): Internal 7V Regulator Output. The main and PWM gate drivers and control circuits are powered from this voltage. Decouple this pin locally to the IC ground with a minimum of 4.7 µF low ESR ceramic capacitor. VIN (Pin 11): Main Supply Pin. Must be closely decoupled to ground. SENSE (Pin 12): Current Sense Input for the Control Loop. Connect this pin to the drain of the main power MOSFET for VDS sensing and highest efficiency for VSENSE ≤ 36V. Alternatively, the SENSE pin may be connected to a resistor in the source of the main power MOSFET. Internal leading-edge blanking is provided for both sens- ing methods. SS (Pin 13): Soft-Start Pin. Provides a 50 µA pull-up current, enabled and reset by RUN, which charges an optional external capacitor. This voltage ramp translates into a corresponding current limit ramp through the main MOSFET. OV/FB (Pin 14): Overvoltage Pin/Voltage Feedback Pin. In voltage mode (VFBP ≤ VREF), this input, connected to VOUT through a resistor network, sets the output voltage at which GATE switching is disabled in order to prevent an overvoltage situation. Nominal threshold voltage for the OV pin is 1.32V (VREF + 7%) with 20mV hysteresis. In current/voltage mode (VFBP > 2.5V), this pin senses VOUT through a resistor divider and brings the loop into voltage regulation such that pin voltage approaches VREF = 1.23V, provided the loop is not regulating the load current (e.g., [VFBP – VFBN] < 100mV for ILIM = 1.23V). |
Similar Part No. - LTC4002 |
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Similar Description - LTC4002 |
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