Datasheet LTC3789 (Analog Devices) - 9

LTC3789
pin FuncTions (SSOP/QFN) VFB (Pin 1/Pin 26):
Error Amplifier Feedback Pin. Receives
FREQ (Pin 8/Pin 5):
Frequency Set Pin. There is a precision the feedback voltage for the controller from an external 10µA current flowing out of this pin. A resistor to ground resistive divider across the output. sets a voltage which, in turn, programs the frequency.
SS (Pin 2/Pin 27):
External Soft-Start Input. The LTC3789 Alternatively, this pin can be driven with a DC voltage to regulates the V vary the frequency of the internal oscillator. FB voltage to the smaller of 0.8V or the volt- age on the SS pin. A internal 3µA pull-up current source
RUN (Pin 9/Pin 6):
Run Control Input. Forcing the pin is connected to this pin. A capacitor to ground at this below 0.5V shuts down the controller, reducing quies- pin sets the ramp time to final regulated output voltage. cent current. There are 1.2µA pull-up currents for this
SENSE+ (Pin 3/Pin 28):
The (+) Input to the Current Sense pin. Once the RUN pin rises above 1.22V, the IC is turned Comparator. The I on, and an additional 5µA pull-up current is added to TH pin voltage and controlled offsets between the SENSE– and SENSE+ pins, in conjunction the pin. with RSENSE, set the current trip threshold.
VINSNS (Pin 10/Pin 7):
VIN Sense Input to the Buck-Boost
SENSE– (Pin 4/Pin 1):
The (–) Input to the Current Sense Transition Comparator. Connect this pin to the drain of the Comparator. top N-channel MOSFET on the input side.
I VOUTSNS (Pin 11/Pin 8):
VOUT Sense Input to the Buck-
TH (Pin 5/Pin 2):
Error Amplifier Output and Switch- ing Regulator Compensation Point. The channel’s Boost Transition Comparator. Connect this pin to the VOUT. current comparator trip point increases with this control
ILIM (Pin 12/Pin 9):
Input/Output Average Current voltage. Sense Range Input. This pin tied to SGND, INTVCC or
SGND (Pin 6/Pins 3, Exposed Pad Pin 29):
Small left floating, sets the maximum average current sense Signal Ground. Must be routed separately from high threshold. current grounds to the common (–) terminals of the
I + OSENSE (Pin 13/Pin 10):
The (+) Input to the Input/Output CIN capacitors. In the QFN package, the exposed pad Average Current Sense Amplifier. is SGND. It must be soldered to PCB ground for rated
I – (Pin 14/Pin 11):
The (–) Input to the Input/Output thermal performance.
OSENSE
Average Current Sense Amplifier.
MODE/PLLIN (Pin 7/Pin 4):
Mode Selection or External
TRIM (Pin 15/Pin 12):
Tie this pin to GND for normal Synchronization Input to Phase Detector. This is a dual- operation. Do not allow this pin to float. purpose pin. When external frequency synchronization is not used, this pin selects the operating mode. The
EXTVCC (Pin 20/Pin 17):
External Power Input to an pin can be tied to SGND or INTVCC. SGND or below Internal LDO Connected to INTVCC. This LDO supplies 0.8V enables forced continuous mode. INTVCC enables INTVCC power, bypassing the internal LDO powered from pulse-skipping mode. For external sync, apply a clock VIN whenever EXTVCC is higher than 4.8V. See EXTVCC signal to this pin. The internal PLL will synchronize the Connection in the Applications Information section. Do internal oscillator to the clock, and forced continuous not exceed 14V on this pin. mode will be enabled. The PLL composition network is integrated into the IC. 3789fc For more information www.linear.com/LTC3789 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration order information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Typical Application Related Parts