LTC1435A Linear Technology, LTC1435A Datasheet - Page 6

• Manufacturer Part Number: LTC1435A
• Description: High Efficiency Low Noise Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

FUNCTIONAL DIAGRA
Main Control Loop
The LTC1435A uses a constant frequency, current mode
step-down architecture. During normal operation, the top
MOSFET is turned on each cycle when the oscillator sets
the RS latch, and turned off when the main current com-
parator I
which I
the I
V
EA to receive an output feedback voltage V
ternal resistive divider. When the load current increases,
it causes a slight decrease in V
OPERATION
LTC1435A
6
OSENSE
U
TH
V
1
pin , which is the output of error amplifier EA. The
R2
OSENSE
1
resets the RS latch is controlled by the voltage on
pin, described in the Pin Functions section, allows
6
* FOLDBACK CURRENT LIMITING OPTION
resets the RS latch. The peak inductor current at
R1
1.19V
V
3 A
FB
6V
U
+
–
2
U
EA
RUN/SS
SHUTDOWN
C
1.28V
SS
g
START
m
SOFT
RUN
= 1m
(Refer to Functional Diagram)
+
–
R
C
C
C
OV
3
FB
I
D
TH
FB
relative to the 1.19V ref-
180k
30k
OSC
*
1
W
C
+
–
OSC
I
1
C
FB
–
+
OSC
S
R
from an ex-
Q
SENSE
0.6V
8k
4k
+
8
+
–
1 A
1.19V
4
7
INTV
SENSE
SFB
4.8V
–
+
–
+
CC
erence, which in turn causes the I
the average inductor current matches the new load current.
While the top MOSFET is off, the bottom MOSFET is turned
on until either the inductor current starts to reverse, as
indicated by current comparator I
next cycle.
The top MOSFET driver is biased from floating bootstrap
capacitor C
cycle. However, when V
V
the top MOSFET continuously. The dropout detector counts
the number of oscillator cycles that the top MOSFET remains
SHUTDOWN
DROP
–
OUT
DET
OUT
+
–
I
2
, the loop may enter dropout and attempt to turn on
LDO
REG
SWITCH
V
5V
LOGIC
1.19V
IN
B
REF
13
, which normally is recharged during each off
V
IN
9
EXTV
SGND
CC
IN
5
decreases to a voltage close to
INTV
BOOST
PGND
SW
TG
BG
TH
C
15
16
14
12
11
10
D1
IN
2
CC
INTV
, or the beginning of the
+
voltage to increase until
V
+
IN
CC
D
C
B
B
R
SENSE
C
C
V
SEC
V
OUT
SEC
OUT
1435A • FD
+
+