link to page 21 link to page 21 LT3932/LT3932-1 PIN FUNCTIONS VIN: Input Voltage Pins. These pins supply power to the VREF: Reference Voltage Pin. This pin provides a buffered internal, high performance analog circuitry, and they sup- 2V reference capable of 1mA drive. It can be used to sup- ply the inductor current when the internal high side power ply resistor networks for setting the voltages at the CTRL switch is on. Connect capacitors between these pins and and PWM pins. Bypass with a 2.2μF capacitor to GND. GND and see Selecting and Placing the Input Capacitors FB: Feedback Pin. When the voltage at this pin is near 1V, in Applications Information for advice regarding their the regulated current is automatically reduced from the placement. programmed value. A resistor network between this pin EN/UVLO: Enable and Undervoltage Lockout Pin. A volt- and VOUT can be used to set a limit for the output voltage. age at this pin greater than 1.15V will enable switching, If the voltage at the FB pin reaches 1.05V, an overvoltage and a voltage less than 300mV is guaranteed to shut down lockout comparator disables switching. the internal current bias and sub-regulators. A resistor FAULT: Fault Pin. Connect to INTV network between this pin and V CC through a resistance IN can be used to set the of 100k. When the FB pin voltage is less than 200mV, an pin voltage and automatically lockout the part when VIN is internal switch pulls this pin low to indicate a short-circuit. below a certain level. No internal components pull up or When FB is greater than 950mV and the voltage between down on this pin, so it requires an external voltage bias ISP and ISN is simultaneously less than 10mV, the switch for normal operation. This pin may be tied directly to VIN. pulls this pin low to indicate an open-circuit. INTVCC: Internal y Regulated, Low-Voltage Supply Pin. SS: Soft-Start Pin. At startup and recovery from fault con- This pin provides the power for the converter switch gate ditions, a 20μA current charges the capacitor and the FB drivers. Do not force any voltage on this pin, but bypass voltage tracks the rising voltage at this pin until the load it with a 2.2µF capacitor to GND. current reaches its programmed level. Typical values for ISP: Positive Current Sense Pin. This pin is one of the the capacitor are 10nF to 100nF. A resistor from SS to inputs to the internal current sense error amplifier. It INTVCC is used to select one of several fault modes. See should be connected to the positive side of the external Soft-Start and Fault Modes in Applications Information sense resistor. for more details. ISN: Negative Current Sense Pin. This pin is one of the VC: Compensation Pin. A capacitor connected from this inputs to the internal current sense error amplifier. It pin to GND stabilizes the current and voltage regulation. should be connected to the negative side of the external See Stabilizing the Regulation Loop in the Applications sense resistor. Information section for more details. ISMON: Output Current Monitoring Pin. This pin provides SW: Switch Pins. These two pins are internally connected a buffered voltage output equal to 10mV for every 1mV to the power devices and drivers. They should always be between ISP and ISN. tied together. In normal operation, the voltage of these CTRL: Control Pin. An analog voltage from 250mV to pins will switch between the input voltage and zero at 1.25V at this pin programs the regulated voltage between the programmed frequency. Do not force any voltage on ISP and ISN (and therefore, the regulated current supplied these pins. to the load). Alternatively, a digital pulse at this pin with RT: Timing Resistor Pin. A resistor from this pin to GND duty cycle from 12.5% to 62.5% can be used to pro- programs the switching frequency between 200kHz and gram the regulated voltage. Below 200mV or 10% duty 2MHz. Do not leave this pin open. cycle, the CTRL pin voltage disables switching. For more detail, see Regulated LED Current in Typical Performance Curves and Programming LED Current with the CTRL Pin in Applications Information. Rev B 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Block Diagram Operation Typical Applications Package Description Revision History Typical Application Related Parts
