LTC3785 LINER [Linear Technology], LTC3785 Datasheet - Page 8

• Manufacturer Part Number: LTC3785
• Description: High Efficiency, Synchronous, 4-Switch Buck-Boost Controller
• Manufacturer: LINER [Linear Technology]

LTC3789
Typical perForMance characTerisTics
8
pin FuncTions
V
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
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
Comparator. The I
between the SENSE
with R
SENSE
Comparator.
I
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 the QFN package, the exposed pad is SGND. It must be
soldered to PCB ground for rated thermal performance.
TH
FB
(Pin 5/Pin 2): Error Amplifier Output and Switching
(Pin 1/Pin 26): Error Amplifier Feedback Pin. Receives
SENSE
+
–
(Pin 3/Pin 28): The (+) Input to the Current Sense
(Pin 4/Pin 1): The (–) Input to the Current Sense
500mV/DIV
30V TO 5V
V
OUT
, set the current trip threshold.
2A/DIV
V
(AC)
V
ITH
FB
IN
I
L
Line Transient
voltage to the smaller of 0.8V or the
TH
–
pin voltage and controlled offsets
and SENSE
(SSOP/QFN)
1ms/DIV
+
pins, in conjunction
IN
3789 G28
capacitors.
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
forced continuous mode. INTV
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
Transition Comparator. Connect this pin to the drain of the
top N-channel MOSFET on the input side.
INSNS
500mV/DIV
5V TO 30V
V
OUT
2A/DIV
V
(AC)
(Pin 10/Pin 7): V
V
ITH
IN
I
L
Line Transient
T
A
= 25°C unless otherwise noted.
1ms/DIV
CC
IN
. SGND or below 0.8V enables
Sense Input to the Buck-Boost
CC
enables pulse-skipping
3789 G29
3789f