Datasheet LTC7891 (Analog Devices) - 7

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LTC7891 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 3. Pin Configuration Table 3. Pin Function Descriptions Pin No. Mnemonic Description
1 PLLIN/SPREAD External Synchronization Input to Phase Detector/Spread Spectrum Enable. When an external clock is applied to PLLIN/SPREAD, the phase-locked loop forces the rising TGxx signal to synchronize with the rising edge of the external clock. When not synchronizing to an external clock, tie this input to INTVCC to enable spread spectrum dithering of the oscillator, or to GND to disable spread spectrum dithering. 2 MODE Mode Select Input. This input determines how the LTC7891 operates at light loads. Connect MODE to GND to select the Burst Mode operation. An internal 100 kΩ resistor to GND also invokes Burst Mode operation when MODE is floating. Connect MODE to INTVCC to force continuous inductor current operation. Tying MODE to INTVCC through a 100 kΩ resistor selects the pulse skipping operation. 3 FREQ Frequency Control Pin for the Internal Voltage Controlled Oscillator (VCO). Connect FREQ to GND for a fixed frequency of 370 kHz. Connect FREQ to INTVCC for a fixed frequency of 2.25 MHz. Program frequencies between 100 kHz and 3 MHz by using a resistor between FREQ and GND. Minimize the capacitance on FREQ. 4 TRACK/SS External Tracking/Soft Start Input. TRACK/SS regulates the VFB voltage to the lesser of 0.8 V or the voltage on the TRACK/SS pin. An internal 12 µA pull-up current source is connected to TRACK/SS. A capacitor to GND at TRACK/SS sets the ramp time to the final regulated output voltage. The ramp time is equal to 1 ms for every 12.5 nF of capacitance. Alternatively, a resistor divider on another voltage supply connected to TRACK/SS allows the output to track the other supply during startup. 5 TEST Test Pin. This pin must be soldered to PCB GND. 6 VPRG Output Voltage Control Pin. VPRG sets the adjustable output mode using external feedback resistors or the fixed 12 V or 5 V output mode. Floating VPRG programs the output from 0.8 V to 60 V with an external resistor divider, regulating VFB to 0.8 V. Connect VPRG to INTVCC or GND to program the output to 12 V or 5 V, respectively, through an internal resistor divider on VFB. 7 VIN Main Supply Pin. A bypass capacitor must be tied between VIN and GND. 8 DRVCC Gate Driver Power Supply Pin. The gate drivers are powered from DRVCC. Connect DRVCC to INTVCC by a separate trace to the INTVCC bypass capacitor. 9 BSTVCC Bootstrap Diode Anode Connection Pin. Place an optional external Schottky diode between the BSTVCC and BOOST pins to bypass most of the 7 Ω switch resistance between DRVCC and BOOST. 10 EXTVCC External Power Input to an Internal LDO Regulator Connected to DRVCC. This LDO regulator supplies INTVCC power, bypassing the internal VIN LDO regulator whenever EXTVCC is higher than the EXTVCC switchover voltage. See the EXTVCC connection in the Power and Bias Supplies (VIN, EXTVCC, DRVCC, and INTVCC) section and INTVCC Regulators (OPTI-DRIVE) section. Do not exceed 30 V on EXTVCC. Connect EXTVCC to GND if the EXTVCC LDO regulator is not used. 11 INTVCC Output of the Internal LDO Regulator. The INTVCC voltage regulation point is set by the DRVSET pin. INTVCC must be decoupled to GND with a 4.7 µF to 10 µF ceramic or other low equivalent series resistance (ESR) capacitor.
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Document Outline Features Applications Typical Application Circuit General Description Specifications Electrical Characteristics Absolute Maximum Ratings ESD Caution Pin Configuration and Function Descriptions Typical Performance Characteristics Theory of Operation Functional Diagram Main Control Loop Power and Bias Supplies (VIN, EXTVCC, DRVCC, and INTVCC) High-Side Bootstrap Capacitor Dead Time Control (DTCA and DTCB Pins) Startup and Shutdown (RUN and TRACK/SS Pins) Light Load Operation: Burst Mode Operation, Pulse Skipping Mode, or Forced Continuous Mode (MODE Pin) Frequency Selection, Spread Spectrum, and Phase-Locked Loop (FREQ and PLLIN/SPREAD Pins) Output Overvoltage Protection Foldback Current Power Good Applications Information Inductor Value Calculation Inductor Core Selection Current Sense Selection Low Value Resistor Current Sensing Inductor DCR Current Sensing Setting the Operating Frequency Selecting the Light Load Operating Mode Dead Time Control (DTCA and DTCB Pins) DTCx Pins Tied to GND (Adaptive Dead Time Control) DTCx Pins Tied to INTVCC (Smart Near Zero Dead Time Control) DTCx Pins Connected with a Resistor to GND Power FET Selection CIN and COUT Selection Setting the Output Voltage RUN Pin and Undervoltage Lockout Soft Start and Tracking (TRACK/SS Pin) INTVCC Regulators (OPTI-DRIVE) Topside FET Driver Supply (CB) Minimum On Time Considerations Fault Conditions: Current Limit and Foldback Fault Conditions: Overvoltage Protection Fault Conditions: Overtemperature Protection Phase-Locked Loop and Frequency Synchronization Efficiency Considerations Checking Transient Response Design Example PCB Layout Checklist PCB Layout Debugging Typical Applications Related Products Outline Dimensions Ordering Guide Evaluation Boards Automotive Products