Datasheet
LTC3413
6
3413fc
Main Control Loop
The LTC3413 is a monolithic, constant frequency, current
mode step-down DC/DC converter that is capable of sourc-
ing and sinking current at the output. During normal opera-
tion, the internal top power switch (P-channel MOSFET) is
turned on at the beginning of each clock cycle. Current in
the inductor increases until the current comparator trips
and turns off the top power MOSFET. The peak inductor
current at which the current comparator shuts off the top
power switch is controlled by the voltage on the I
TH
pin.
The error amplifi er adjusts the voltage on the I
TH
pin by
comparing the feedback signal on the V
FB
pin with a ref-
erence voltage that is equal to one-half of the voltage on
the V
REF
pin. When the load current increases, it causes
a reduction in the feedback voltage relative to the refer-
ence. The error amplifi er raises the I
TH
voltage until the
average inductor current matches the new load current.
When the top power MOSFET shuts off, the synchronous
power switch (N-channel MOSFET) turns on until either
the bottom current limit is reached or the beginning of the
next clock cycle. The bottom current limit is set at –7A.
The operating frequency is set by an external resistor
connected between the R
T
pin and ground. The switching
frequency can range from 300kHz to 2MHz.
Overvoltage and undervoltage comparators will pull the
PGOOD output low if the output voltage comes out of
regulation by ±10%. In an overvoltage condition, the top
power MOSFET is turned off and the bottom power MOSFET
is switched on until either the overvoltage condition clears
or the bottom MOSFET’s current limit is reached.
Dropout Operation
When the input supply voltage decreases toward the output
voltage, the duty cycle increases toward the maximum
on-time. Further reduction of the supply voltage forces the
–
+
–
+
–
+
–
+
–
+
16
10
9
PV
IN
3
I
TH
6
V
REF
1
8
SV
IN
SGND
4
V
FB
PGOOD
SV
IN
PV
IN
SLOPE
COMPENSATION
RECOVERY
SLOPE
COMPENSATION
PMOS CURRENT
COMPARATOR
NMOS CURRENT
COMPARATOR
OSCILLATOR
ERROR
AMPLIFIER
LOGIC
RUN
RUN/SSR
T
11
14
15
SW
SW
SW
SW
13
75
PGND
3413 BD
12
PGND
2
1.1V
REF
2
0.9V
REF
2
FUNCTIONAL DIAGRAM
OPERATION