Datasheet

LTC3613
10
3613fa
FUNCTIONAL DIAGRAM
–
+
–
+
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
SV
IN
4.2V
TIME
ADJUST
STOP
START
1.2V
0.75V
–
+
+
–
+
DA
(A = 1)
R
PGD
PGOOD
MODE/PLLIN
V
RNG
ITH
V
OSNS
–
V
OSNS
+
TRACK/SS
SENSE
–
SENSE
+
PGND
SW
EXTV
CC
BO0ST
INPUT SUPPLY
D
B
C
B
MT
MB
L
C
OUT
R
FB2
R
FB1
R
SENSE
PV
IN
INTV
CC
INTV
CC
SGND
R
ITH
C
ITH1
INTV
CC
R1
INTV
CC
R2
3.65V
UVLO
4.6V
V
OUT
RT
RT
RUN
1.3µA
C
VCC
V
IN
C
IN
V
OUT
C
IN
C
SS
3613 FD
+
–
UV
+
–
+
–
–
+
–
–
OV
+
–
TG DRV
BG DRV
CLOCK
OPERATION
Main Control Loop
The LTC3613 uses valley current mode control to regulate
the output voltage in a monolithic, 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 resis-
tive (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
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
(Refer to Functional Diagram)