LTC3568_15 Datasheet, PDF (6/18 Pages) Linear Technology – 1.8A, 4MHz, Synchronous Step-Down DC/DC Converter

LTC3568
Pin Functions
SHDN/R_T (Pin 1): Combination Shutdown and Timing
Resistor Pin. The oscillator frequency is programmed by
connecting a resistor from this pin to ground. Forcing
this pin to SV_IN causes the device to be shut down. In
shutdown all functions are disabled.
SYNC/MODE (Pin 2): Combination Mode Selection and
Oscillator Synchronization Pin. This pin controls the op-
eration of the device. When tied to SV_IN or SGND, Burst
Mode operation or pulse skipping mode is selected,
respectively. If this pin is held at half of SV_IN, the forced
continuous mode is selected. The oscillation frequency
can be syncronized to an external oscillator applied to
this pin. When synchronized to an external clock pulse
skip mode is selected.
SGND (Pin 3): The Signal Ground Pin. All small signal
components and compensation components should be con-
nected to this ground (see Board Layout Considerations).
SW (Pin 4): The Switch Node Connection to the Inductor.
This pin swings from PV_IN to PGND.
PGND (Pin 5): Main Power Ground Pin. Connect to the
(–) terminal of C_OUT, and (–) terminal of C_IN.
PV_IN (Pin 6): Main Supply Pin. Must be closely decoupled
to PGND.
SV_IN (Pin 7): The Signal Power Pin. All active circuitry
is powered from this pin. Must be closely decoupled to
SGND. SV_IN must be greater than or equal to PV_IN.
PGOOD (Pin 8): The Power Good Pin. This common drain
logic output is pulled to SGND when the output voltage is
not within ±7.5% of regulation.
V_FB (Pin 9): Receives the feedback voltage from the ex-
ternal resistive divider across the output. Nominal voltage
for this pin is 0.8V.
I_TH (Pin 10): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.5V.
GND (Exposed Pad Pin 11): Thermal Ground. Con-
nect to SGND and solder to the PCB for rated thermal
performance.
Block Diagram
SV_IN
SGND
I_TH
7
3
10
V_FB 9
0.8V _VOLTAGE
REFERENCE
+
–
0.74V +
ERROR
AMPLIFIER
V_B
–
I_TH
LIMIT
BCLAMP
–
+
BURST
COMPARATOR
HYSTERESIS = 80mV
OSCILLATOR
PV_IN
6
PMOS CURRENT
COMPARATOR
+
–
SLOPE
COMPENSATION
4 SW
PGOOD 8
+
0.86V –

1
SHDN/R_T
+
LOGIC
–
NMOS
COMPARATOR
–
+
REVERSE
COMPARATOR
2
SYNC/MODE
5 PGND
3568 BD
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