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LTC1435AI Folha de dados(PDF) 6 Page - Linear Technology

Nome de Peças LTC1435AI
Descrição Electrónicos  High Efficiency Low Noise Synchronous Step-Down Switching Regulator
PDF  20 Pages
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Fabricante Electrônico  LINER [Linear Technology]
Página de início  http://www.linear.com
Logo LINER - Linear Technology

LTC1435AI Folha de dados(HTML) 6 Page - Linear Technology

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LTC1435A
FUNCTIONAL DIAGRA
–
+
+
–
+
–
+
–
SWITCH
LOGIC
DROP
OUT
DET
0.6V
1.19V
Q
S
R
I1
INTVCC
4k
–
+
8k
180k
30k
+
–
–
+
EA
SHUTDOWN
6V
3
µA
1.19V
1.28V
–
+
4.8V
VIN
SHUTDOWN
1.19V
REF
CSS
CC
RC
RUN/SS
2
ITH
3
DFB*
SENSE+
7
8
SENSE–
EXTVCC
9
+
R2
VOSENSE
OV
1
µA
OSC
PGND
10
BG
INTVCC
12
SW
14
TG
16
BOOST
SGND
VIN
13
SFB
4
COSC
1
RSENSE
+
+
VSEC
CSEC
VOUT
COUT
D1
CB
DB
INTVCC
+
CIN
VIN
COSC
5V
LDO
REG
RUN
SOFT
START
1435A • FD
VFB
R1
I2
gm = 1m
* FOLDBACK CURRENT LIMITING OPTION
5
6
11
15
(Refer to Functional Diagram)
OPERATION
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 I1 resets the RS latch. The peak inductor current at
which I1 resets the RS latch is controlled by the voltage on
the ITH pin , which is the output of error amplifier EA. The
VOSENSEpin, described in the Pin Functions section, allows
EA to receive an output feedback voltage VFB from an ex-
ternal resistive divider. When the load current increases,
it causes a slight decrease in VFB relative to the 1.19V ref-
erence, which in turn causes the ITHvoltagetoincreaseuntil
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 I2, or the beginning of the
next cycle.
The top MOSFET driver is biased from floating bootstrap
capacitor CB, which normally is recharged during each off
cycle. However, when VIN decreases to a voltage close to
VOUT, the loop may enter dropout and attempt to turn on
the top MOSFET continuously. The dropout detector counts
the number of oscillator cycles that the top MOSFET remains



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