LTC3826-1 Datasheet, PDF (9/32 Pages) Linear Technology – 30μA IQ, Dual, 2-Phase Synchronous Step-Down Controller

LTC3826-1
FUNCTIONAL DIAGRAM
PLLIN/MODE
F_IN
6
PHASE DET
100k
PLLLPF
5
R_LP
C_LP
OSCILLATOR
CLK1
CLK2
0.88V
PGOOD1
27
V_FB1
0.72V
INTV_CC-0.5V –
+
PLLIN/MODE
–
0.8V +
FC
BURSTEN
V_IN
V_IN
22
EXTV_CC
20
INTV_CC
+ ¹⁹
SGND
7
4.7V +
–
5.25V/
7.5V
LDO
INTERNAL
SUPPLY
DUPLICATE FOR SECOND
CONTROLLER CHANNEL
S
R
INTV_CC
BOOST
D_B
24, 17
DROP
OUT
DET
BOT FC
TG
C_B
TOP
26, 15
TOP ON
SW
Q
Q
SWITCH
LOGIC
INTV_CC
25, 16
BG
BOT
BURSTEN
0.4V + ^B
SLEEP
23, 18
PGND
21
–
SHDN
L
V_IN
D
C_IN
C_OUT
R_SENSE
ICMP
–
0.45V
2(V_FB)
SLOPE
COMP
IR
–
++ –
+
6mV
EA
OV
V_FB
TRACK/SS
0.80V
SENSE⁺
3, 11
SENSE^–
4, 10
V_FB
2, 12
0.5μA
6V
RUN
8, 9
SHDN
RST
2(V_FB)
0.88V
FOLDBACK
1μA
SHDN
I_TH
1,13
TRACK/SS
28,14
R_B
R_A
C_C
C_C2
R_C
C_SS
V_OUT
38261 FD
OPERATION (Refer to Functional Diagram)
Main Control Loop
The LTC3826-1 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, I_CMP, resets the RS
latch. The peak inductor current at which I_CMP trips and
resets the latch is controlled by the voltage on the I_TH pin,
which is the output of the error amplifier EA. The error
amplifier compares the output voltage feedback signal at
the V_FB pin, (which is generated with an external resistor
divider connected across the output voltage, V_OUT, to
ground) to the internal 0.800V reference voltage. When the
load current increases, it causes a slight decrease in V_FB
relative to the reference, which causes the EA to increase
the I_TH voltage until the average inductor current matches
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.
38261fb
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