Datasheet

LTC3833
10
3833f
FUNCTIONAL DIAGRAM
Main Control Loop
The LTC3833 uses valley current mode control to regulate
the output voltage in an all N-channel MOSFET DC/DC step-
down converter. Current control is achieved by sensing
the inductor current across SENSE
+
and SENSE
–
, either
by using an explicit resistor connected in series with the
inductor or by implicitly sensing the inductor’s resistive
(DCR) voltage drop through an RC filter connected across
the inductor.
In normal steady-state operation, the top MOSFET is turned
on for a fixed time interval proportional to the delay in the
–
+
–
+
I
CMP
EA
(g
m(EA)
= 1.7mS)
0.645V
0.555V
0.6V
1µA
I
REV
LOGIC
CONTROL
PLL
SYSTEM
ONE-SHOT
TIMER
CLOCK
DETECT
OSCILLATOR
LDO
OUT EN
IN
V
IN
4.2V
TIME
ADJUST
STOP
START
1.2V
0.75V
–
+
+
–
+
DA
(A = 1)
R
PGD
PGOOD
MODE/PLLIN
V
RNG
I
TH
V
OSNS
–
V
OSNS
+
TRACK/SS
SENSE
–
SENSE
+
PGND
SW
EXTV
CC
BO0ST
D
B
C
B
MT
MB
L
C
OUT
R
FB2
R
FB1
R
SENSE
INTV
CC
INTV
CC
BG
TG
SGND
R
ITH
C
ITH1
INTV
CC
R1
INTV
CC
R2
3.65V
UVLO
4.6V
V
OUT
RT
R
T
RUN
1.3µA
C
VCC
V
IN
C
IN
V
OUT
C
SS
3833 FD
+
–
UV
+
–
+
–
–
+
–
–
OV
+
–
TG DRV
BG DRV
CLOCK
OPERATION
one-shot timer. The PLL system adjusts the delay in the
one-shot timer until the top MOSFET turn-on is synchro-
nized either to the internal oscillator or the external clock
input if provided. As the top MOSFET turns off, the bottom
MOSFET turns on with a small time delay (dead time) to
avoid shoot-through current. The next switching cycle is
initiated when the current comparator, I
CMP
, senses that
inductor current has reached the valley threshold point
and turns the bottom MOSFET off immediately and the
top MOSFET on. Again in order to avoid shoot-through
current there is a small dead-time delay before the top
MOSFET turns on.
(Refer to Functional Diagram)