Datasheet LTC7803 (Analog Devices) - 9

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PIN FUNCTIONS (MSOP/QFN) TRACK/SS (Pin 1/Pin 3):
External Tracking and Soft-Start
PLLIN/SPREAD (Pin 8/Pin 10):
External Synchronization Input. The LTC7803 regulates the VFB voltage to the lesser Input and Spread Spectrum Selection. When an external of 0.8V or the voltage on the TRACK/SS pin. An internal clock is applied to this pin, the phase-locked loop will 12.5µA pull-up current source is connected to this pin. force the rising TG signal to be synchronized with the A capacitor to ground at this pin sets the ramp time to rising edge of the external clock. When an external clock the final regulated output voltage. The ramp time is equal is present, the regulators operate in pulse-skipping mode to 0.65ms for every 10nF of capacitance. Alternatively, a if it is selected by the MODE pin, or in forced continuous resistor divider on another voltage supply connected to mode otherwise. When not synchronizing to an external the TRACK/SS pin allows the LTC7803 output to track the clock, tie this input to INTVCC to enable spread spectrum other supply during start-up. dithering of the oscillator or to ground to disable spread
SENSE+ (Pin 2/Pin 4):
The Positive (+) Input to the spectrum. Differential Current Comparators. The ITH pin voltage and
MODE (Pin 9/Pin 11):
Mode Select Input. This input controlled offsets between the SENSE– and SENSE+ pins determines how the LTC7803 operates at light loads. in conjunction with RSENSE set the current trip threshold. Pulling this pin to ground selects Burst Mode operation.
SENSE– (Pin 3/Pin 5):
The Negative (–) Input to the An internal 100k resistor to ground also invokes Burst Differential Current Comparators. When SENSE– is Mode operation when the pin is floating. Tying this pin greater than INTV to INTVCC forces continuous inductor current operation. CC, the SENSE– pin supplies current to the current comparator. When SENSE– is 3.2V or greater, Tying this pin to INTVCC through a 100k resistor selects it supplies the majority of the sleep mode quiescent cur- pulse-skipping operation. rent instead of VIN, further reducing the input-referred
INTVCC (Pin 10/Pin 12):
Output of the Internal 5.15V Low quiescent current. Dropout Regulator (LDO). The driver and control circuits
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are powered by this supply. Must be decoupled to GND
FB (Pin 4/Pin 6):
Error Amplifier Feedback Input. Connect an external resistor divider between the output voltage with a minimum of 4.7μF ceramic or tantalum capacitor. and the VFB pin to set the regulated output voltage.
EXTVCC (Pin 11/Pin 13):
External Power Input to an
ITH (Pin 5/Pin 7):
Error Amplifier Output and Switching Internal LDO Connected to INTVCC. This LDO supplies Regulator Compensation Point. The current comparator INTVCC power, bypassing the internal LDO powered from trip point increases with this control voltage. Place com- VIN whenever EXTVCC is higher than 4.7V. See INTVCC pensation components between the ITH pin and GND. Regulators in the Applications Information section. Do not exceed 30V on this pin. Tie this pin to GND if the EXTVCC
RUN (Pin 6/Pin 8):
Run Control Input. Forcing this pin LDO is not used. below 1.2V disables switching of the corresponding controller. Forcing this pin below 0.7V shuts down the
VIN (Pin 12/Pin 14):
Main Bias Input Supply Pin. A bypass LTC7803, reducing quiescent current to approximately capacitor should be tied between this pin and GND. 1.2µA. This pin can be tied to VIN for always-on operation.
BG (Pin 13/Pin 15):
High Current Gate Drive for Bottom
FREQ (Pin 7/Pin 9):
Frequency Control pin for the inter- (Synchronous) N-Channel MOSFET. Voltage swing at this nal VCO. Connecting the pin to GND forces the VCO to pin is from GND to INTVCC. a fixed low frequency of 375kHz. Connecting the pin
BOOST(Pin 14/Pin 16):
Bootstrapped Supply to the Top to INTVCC forces the VCO to a fixed high frequency of Side Floating Driver. Connect a capacitor between the 2.25MHz. Frequencies between 100kHz and 3MHz can BOOST and SW pin. Also connect a low leakage Schottky be programmed using a resistor between FREQ and GND. diode between the BOOST and INTVCC pins. Minimize the capacitance on this pin. Rev 0 For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Package Description Typical Application Related Parts