ltc3730 Linear Technology Corporation, ltc3730 Datasheet - Page 9

• Manufacturer Part Number: ltc3730
• Description: 3-phase, 5-bit Intel Mobile Vid, 600khz, Synchronous Buck Controller
• Manufacturer: Linear Technology Corporation

FU CTIO AL DIAGRA
OPERATIO
Main Control Loop
The IC uses a constant frequency, current mode step-
down architecture. During normal operation, each top
MOSFET is turned on each cycle when the oscillator sets
the RS latch, and turned off when the main current
comparator, I
current at which I
voltage on the I
amplifier EA. The EAIN pin receives a portion of this
voltage feedback signal via the AMPOUT pin through the
U
PGOOD
F
IN
R
C
LP
LP
U
1
PLLFLTR
, resets each RS latch. The peak inductor
AMPOUT
R
PLLIN
EAIN
C
C
FCB
TH
IN
IN
I
DELAY
TH
C
100µs
1
+
–
U
0.600V
0.660V
PROTECTION
resets the RS latch is controlled by the
VID0 VID1 VID2 VID3 VID4
0.6V
pin, which is the output of the error
50k
5-BIT VID DECODER
(Refer to Functional Diagram)
V
FB
+
–
OSCILLATOR
PHASE DET
–
+
+
–
EA
OV
FCB
–
+
R2 VARIABLE
A1
–
+
–
+
W
CLK1
CLK2
CLK3
0.66V
0.54V
EAIN
20k
R1
DUPLICATE FOR SECOND AND THIRD
CONTROLLER CHANNELS
LATCH
RS
V
CC
5(V
0.86V
6V
FB
SLOPE
COMP
1.5µA
CLAMP
)
S
R
SS
I
0.55V
1
5(V
–
+
SHDN
Q
Q
RST
Figure 2
FB
–
2.4V
)
DROP
OUT
DET
+
B
internal VID DAC and is compared to the internal reference
voltage. When the load current increases, it causes a slight
decrease in the EAIN pin voltage relative to the 0.6V
reference, which in turn causes the I
until each inductor’s average current matches one third of
the new load current (assuming all three current sensing
resistors are equal). In Burst Mode operation and stage
shedding mode, after each top MOSFET has turned off, the
bottom MOSFET is turned on until either the inductor
current starts to reverse, as indicated by current compara-
tor I
+
START
SOFT-
54k
SHED
RUN
3mV
BOT
FORCE BOT
–
2
SHDN
, or the beginning of the next cycle.
FCB
54k
UV RESET
–
+
I
2
INTERNAL
SWITCH
LOGIC
SUPPLY
0.600V
TOP
BOT
V
V
CC
36k
36k
V
CC
REF
SENSE
SENSE
BOOST
RUN/SS
PGND
SGND
V
SW
TG
BG
CC
+
–
+
V
R
CC
V
SENSE
CC
C
C
D
CC
SS
C
B
B
L
TH
V
IN
voltage to increase
LTC3730
+
C
IN
3730fa
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