LTC3412
U
U
W
FU CTIO AL BLOCK DIAGRA
PV
IN
SV
SGND
8
I
TH
3
IN
1
9
16
SLOPE
COMPENSATION
RECOVERY
PMOS CURRENT
COMPARATOR
VOLTAGE
REFERENCE
0.8V
BCLAMP
+
–
+
–
–
+
P-CH
4
V
FB
ERROR
AMPLIFIER
BURST
COMPARATOR
+
–
SYNC/MODE
+
–
0.74V
10
SLOPE
11
COMPENSATION
OSCILLATOR
SW
14
15
+
–
RUN/SS
PGOOD
7
2
RUN
0.86V
N-CH
LOGIC
+
–
NMOS
CURRENT
COMPARATOR
–
+
REVERSE
CURRENT
12
PGND
COMPARATOR
13
5
6
3412 FBD
R
SYNC/MODE
T
U
OPERATIO
Main Control Loop
current increases, it causes a reduction in the feedback
voltage relative to the reference. The error amplifier raises
the ITH 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.
TheLTC3412isamonolithic, 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 ITH pin.
The error amplifier adjusts the voltage on the ITH pin by
comparing the feedback signal from a resistor divider on
the VFB pin with an internal 0.8V reference. When the load
The operating frequency is set by an external resistor
connected between the RT pin and ground. The practical
switching frequency can range from 300kHz to 4MHz.
3412fb
7
Linear [ Linear ]
