LTC3789 Datasheet, PDF (8/28 Pages) Linear Technology – High Efficiency, Synchronous, 4-Switch Buck-Boost Controller

LTC3789
Typical Performance Characteristics T_A = 25°C unless otherwise noted.
Line Transient
V_ITH
V_IN
30V TO 5V
V_OUT (AC)
500mV/DIV
I_L
2A/DIV
Line Transient
V_ITH
V_IN
5V TO 30V
V_OUT (AC)
500mV/DIV
I_L
2A/DIV
1ms/DIV
3789 G28
1ms/DIV
3789 G29
Pin Functions (SSOP/QFN)
V_FB (Pin 1/Pin 26): Error Amplifier Feedback Pin. Receives
the feedback voltage for the controller from an external
resistive divider across the output.
SS (Pin 2/Pin 27): External Soft-Start Input. The LTC3789
regulates the V_FB voltage to the smaller of 0.8V or the
voltage on the SS pin. A internal 3µA pull-up current
source is connected to this pin. A capacitor to ground
at this pin sets the ramp time to final regulated output
voltage.
SENSE⁺ (Pin 3/Pin 28): The (+) Input to the Current Sense
Comparator. The I_TH pin voltage and controlled offsets
between the SENSE^– and SENSE⁺ pins, in conjunction
with R_SENSE, set the current trip threshold.
SENSE^– (Pin 4/Pin 1): The (–) Input to the Current Sense
Comparator.
I_TH (Pin 5/Pin 2): Error Amplifier Output and Switching
Regulator Compensation Point. The channel’s current com-
parator trip point increases with this control voltage.
SGND (Pin 6/Pins 3, Exposed Pad Pin 29): Small Signal
Ground. Must be routed separately from high current
grounds to the common (–) terminals of the C_IN capacitors.
In the QFN package, the exposed pad is SGND. It must be
soldered to PCB ground for rated thermal performance.
MODE/PLLIN (Pin 7/Pin 4): Mode Selection or External
Synchronization Input to Phase Detector. This is a dual-
purpose pin. When external frequency synchronization is
not used, this pin selects the operating mode. The pin can
be tied to SGND or INTV_CC. SGND or below 0.8V enables
forced continuous mode. INTV_CC enables pulse-skipping
mode. For external sync, apply a clock signal to this pin;
the internal PLL will synchronize the internal oscillator
to the clock. The PLL composition network is integrated
into the IC.
FREQ (Pin 8/Pin 5): Frequency Set Pin. There is a precision
10µA current flowing out of this pin. A resistor to ground
sets a voltage which, in turn, programs the frequency.
Alternatively, this pin can be driven with a DC voltage to
vary the frequency of the internal oscillator.
RUN (Pin 9/Pin 6): Run Control Input. Forcing the pin
below 0.5V shuts down the controller, reducing quiescent
current. There are 1.2µA pull-up currents for this pin.
Once the RUN pin rises above 1.22V, the IC is turned on,
and an additional 5µA pull-up current is added to the pin.
V_INSNS (Pin 10/Pin 7): V_IN Sense Input to the Buck-Boost
Transition Comparator. Connect this pin to the drain of the
top N-channel MOSFET on the input side.
3789f
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