Datasheet

LTC3412
7
3412fb
–
+
2
7
4
–
+
+
–
–
+
0.74V
ERROR
AMPLIFIER
SYNC/MODE
BURST
COMPARATOR
BCLAMP
NMOS
CURRENT
COMPARATOR
PMOS CURRENT
COMPARATOR
REVERSE
CURRENT
COMPARATOR
0.86V
RUNRUN/SS
15
13
12
14
11
SW
P-CH
N-CH
10
PGOOD
3
I
TH
V
FB
0.8V
5
R
T
6
SYNC/MODE
3412 FBD
16
PV
IN
98
SGND
1
SV
IN
SLOPE
COMPENSATION
VOLTAGE
REFERENCE
OSCILLATOR
LOGIC
SLOPE
COMPENSATION
RECOVERY
–
+
–
+
+
–
PGND
+
–
FU CTIO AL BLOCK DIAGRA
UU
W
OPERATIO
U
Main Control Loop
The LTC3412 is a monolithic, constant-frequency, current
mode step-down DC/DC converter. 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 amplifier adjusts the voltage on the I
TH
pin by
comparing the feedback signal from a resistor divider on
the V
FB
pin with an internal 0.8V reference. When the load
current increases, it causes a reduction in the feedback
voltage relative to the reference. The error amplifier 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 –2A for forced continuous mode and 0A for
Burst Mode operation.
The operating frequency is set by an external resistor
connected between the R
T
pin and ground. The practical
switching frequency can range from 300kHz to 4MHz.