OMO ElectronicOMO Electronic
Expand menu
Hello, Sign inMy Account
0 Cart

LTC1735CF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32
7
LTC1735
1735fc
PI FU CTIO S
UUU
V
OUT(RIPPLE)
(Burst Mode Operation)
Load Step (Burst Mode Operation) Load Step (Continuous Mode)
V
OUT
50mV/DIV
I
L
5A/DIV
0A TO 10µs/DIV
9A LOAD STEP
FCB = 0V
V
IN
= 15V
V
OUT
= 1.6V
V
OUT
50mV/DIV
I
L
5A/DIV
V
OUT
20mV/DIV
I
L
5A/DIV
FCB = 5V 5µs/DIV
V
IN
= 15V
V
OUT
= 1.6V
10mA TO 10µs/DIV
9A LOAD STEP
FCB = 5V
V
IN
= 15V
V
OUT
= 1.6V
1735 G27 1735 G26 1735 G25
FIGURE 1 FIGURE 1 FIGURE 1I
LOAD
= 1.5A
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Start-Up
V
OUT
1V/DIV
V
RUN/SS
5V/DIV
I
L
5A/DIV
V
IN
= 15V 5ms/DIV
V
OUT
= 1.6V
R
LOAD
= 0.16Ω
V
OUT(RIPPLE)
(Synchronized)
V
OUT
10mV/DIV
I
L
5A/DIV
EXT SYNC f = f
O
10µs/DIV
V
IN
= 15V
V
OUT
= 1.6V
V
OUT
20mV/DIV
I
L
5A/DIV
V
OUT(RIPPLE)
(Burst Mode Operation)
FCB = 5V 50µs/DIV
V
IN
= 15V
V
OUT
= 1.6V
1735 G22 1735 G23 1735 G24
FIGURE 1 FIGURE 1I
LOAD
= 10mA I
LOAD
= 50mA
C
OSC
: External capacitor C
OSC
from this pin to ground sets
the operating frequency.
RUN/SS: Combination of Soft-Start and Run Control In-
puts. A capacitor to ground at this pin sets the ramp time
to full output current. The time is approximately 1.25s/µF.
Forcing this pin below 1.5V causes the device to shut
down. (See Applications Information section for quiescent
current note.) In shutdown all functions, including INTV
CC
,
are disabled. Latchoff overcurrent protection is also in-
voked via this pin as described in the Applications Infor-
mation section.
I
TH
: Error Amplifier Compensation Point. The current
comparator threshold increases with this control voltage.
Nominal voltage range for this pin is 0V to 2.4V.
FCB: Forced Continuous/Synchronization Input. Tie this
pin to ground for continuous synchronous operation, to a
resistive divider from the secondary output when using a
secondary winding or to INTV
CC
to enable Burst Mode
operation at low load currents. Clocking this pin with a
signal above 1.5V
P–P
disables Burst Mode operation but
allows cycle-skipping at low load currents and synchro-
nizes the internal oscillator with the external clock. The
FCB pin must not be driven when the device is shut down
(RUN/SS pin low).
SGND: Small-Signal Ground. All small-signal components
such as C
OSC
, C
SS
, the feedback divider plus the loop com-
pensation resistor and capacitor(s) should single-point tie
to this pin. This pin should, in turn, connect to PGND.
8
LTC1735
1735fc
V
OSENSE
: Receives the feedback voltage from an external
resistive divider across the output.
SENSE
–
: The (–) Input to the Current Comparator.
SENSE
+
: The (+) Input to the Current Comparator. Built-in
offsets between SENSE
–
and SENSE
+
pins in conjunction
with R
SENSE
set the current trip threshold.
PGOOD (LTC1735F Only): Open-Drain Logic Output.
PGOOD is pulled to ground when the voltage on the
V
OSENSE
pin is not within ±7.5% of its set point.
EXTV
CC
: Input to the Internal Switch Connected to INTV
CC
.
This switch closes and supplies V
CC
power whenever
EXTV
CC
is higher than 4.7V. See EXTV
CC
connection in the
Applications Information section. Do not exceed 7V on
this pin and ensure EXTV
CC
≤ V
IN
.
PGND: Driver Power Ground. Connects to the source of
bottom N-channel MOSFET, the anode of the Schottky
diode, and the (–) terminal of C
IN
.
BG: High Current Gate Drive for Bottom
N-Channel MOSFET. Voltage swing at this pin is from
ground to INTV
CC
.
INTV
CC
: Output of the Internal 5.2V Regulator and EXTV
CC
Switch. The driver and control circuits are powered from
this voltage. Decouple to power ground with a 1µF ceramic
capacitor placed directly adjacent to the IC together with a
minimum of 4.7µF tantalum or other low ESR capacitor.
V
IN
: Main Supply Pin. Must be closely decoupled to power
ground.
SW: Switch Node Connection to Inductor and Bootstrap
Capacitor. Voltage swing at this pin is from a Schottky
diode (external) voltage drop below ground to V
IN
.
BOOST: Supply to Topside Floating Driver. The bootstrap
capacitor is returned to this pin. Voltage swing at this pin
is from a diode drop below INTV
CC
to (V
IN
+ INTV
CC
).
TG: High Current Gate Drive for Top N-Channel MOSFET.
This is the output of a floating driver with a voltage swing
equal to INTV
CC
superimposed on the switch node voltage
SW.
PI FU CTIO S
UUU
9
LTC1735
1735fc
FU CTIO AL DIAGRA
UU
W
SW
–
+
+
–
0.86V
–
+
0.55V
2.4V
0.8V
0.86V
I
1
+
–
I
2
+
–
EA
A
BURST
DISABLE
FC
OV
gm =1.3m
B
–
+
4.7V
IREV
+
–
+
–
F
FC
S
R
Q
DROP
OUT
DET
0.8V
REF
SWITCH
LOGIC
SD
6V
R1
RUN/SS
C
SS
R
C
V
OSENSE
V
FB
1.2µA
RUN
SOFT-
START
+
OVER-
CURRENT
LATCHOFF
SD
I
TH
C
C
0.17µA
OSC
4(V
FB
)
BUFFERED
I
TH
SLOPE COMP
+– –+
3mV
ICMP
R2
2k
45k
BOT
TOP ON
FORCE BOT
45k
30k 30k
SENSE
+
SENSE
–
SYNC
1.2V 0.8V
C
TOP
UVL
BOT
INTV
CC
5.2V
LDO
REG
V
IN
+
C
INTVCC
V
OUT
V
SEC
INTV
CC
BG
PGND
V
IN
V
IN
BOOST
TG
INTV
CC
C
B
D
B
D
1
C
OSC
+
C
IN
+
C
SEC
+
C
OUT
EXTV
CC
FCBSGNDC
OSC
R
SENSE
1735 FD
PGOOD
LTC1735F
ONLY
Ω
+
–
0.74V
OPERATIO
U
(Refer to Functional Diagram)
Main Control Loop
The LTC1735 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
comparator I
1
resets the RS latch. The peak inductor
current at which I
1
resets the RS latch is controlled by the
voltage on Pin 3 (I
TH
), which is the output of error
amplifier EA. Pin␣ 6 (V
OSENSE
), described in the pin func-
tions, allows EA to receive an output feedback voltage V
FB
from an external resistive divider. When the load current
increases, it causes a slight decrease in V
FB
relative to the
0.8V refer
ence, which in turn causes the I
TH
voltage to
increase until 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
2
, or
the beginning of the next cycle.
The top MOSFET driver is powered from a floating boot-
strap capacitor C
B
. This capacitor is normally recharged
from INTV
CC
through an external diode when the top
MOSFET is turned off. As V
IN
decreases towards V
OUT
, the
converter will attempt to turn on the top MOSFET continu-
ously (“dropout’’). A dropout counter detects this condi-
tion and forces the top MOSFET to turn off for about 500ns
every tenth cycle to recharge the bootstrap capacitor.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32

LTC1735CF

Mfr. #:
Buy LTC1735CF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators LTC1735 - High Efficiency Synchronous Step-Down Switching Regulator
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet