LTC3858-1 Linear Technology Corporation, LTC3858-1 Datasheet - Page 10

• Manufacturer Part Number: LTC3858-1
• Description: Dual 2-Phase Synchronous Step-Down Controller
• Manufacturer: Linear Technology Corporation

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LTC3858-1
FUNCTIONAL DIAGRAM
Main Control Loop
The LTC3858-1 uses a constant frequency, current mode
step-down architecture with the two controller channels
operating 180 degrees out of phase. During normal op-
eration, each external top MOSFET is turned on when the
clock for that channel sets the RS latch, and is turned off
when the main current comparator, ICMP , resets the RS
latch. The peak inductor current at which ICMP trips and
resets the latch is controlled by the voltage on the I
which is the output of the error amplifi er, EA. The error
amplifi er compares the output voltage feedback signal at
OPERATION
10
PLLIN/MODE
PGOOD1
EXTV
FREQ
V
IN
4.7V
CC
+
–
20μA
100k
EN
5.1V
LDO
+
–
+
–
SGND
0.88V
0.72V
V
SYNC
FB1
DET
EN
5.1V
LDO
VCO
INTV
CC
CLK1
CLK2
PFD
DUPLICATE FOR SECOND
CONTROLLER CHANNEL
RUN
TH
10V
2(V
0.5μA
0.45V
pin,
SLOPE COMP
FB
)
ICMP
2(V
SHDN
RST
FB
S
R
0.425V
)
–
+
the V
divider connected across the output voltage, V
ground) to the internal 0.800V reference voltage. When the
load current increases, it causes a slight decrease in V
relative to the reference, which causes the EA to increase
the I
the new load current.
After the top MOSFET is turned off each cycle, the bottom
MOSFET is turned on until either the inductor current starts
to reverse, as indicated by the current comparator IR, or
the beginning of the next clock cycle.
–
SHORT CKT
Q
Q
LATCH-OFF
+
FOLDBACK
DROP
OUT
DET
TH
+
–
FB
3mV
+ –
voltage until the average inductor current matches
pin (which is generated with an external resistor
TOP ON
SHDN
SLEEP
BOT
+
–
OV
IR
SWITCH
SHDN
10μA
LOGIC
EA
+
–
+
–
0.80V
TRACK/SS
0.88V
TOP
BOT
INTV
1μA
CC
SENSE
SENSE
BOOST
PGND
SW
V
TG
BG
I
SS
TH
FB
+
–
INTV
R
CC
A
C
C
C
D
C
C2
R
C
SS
B
B
B
V
L
IN
R
C
D
R
SENSE
C
IN
OUT
38581f
, to
FB