LTC1435CS#TRPBF Linear Technology, LTC1435CS#TRPBF Datasheet - Page 12

• Manufacturer Part Number: LTC1435CS#TRPBF
• Description: IC SW REG SYNC STEP-DOWN 16-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1435CS#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 9 V
• Current - Output: 50mA
• Frequency - Switching: 125kHz
• Voltage - Input: 3.5 ~ 30 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC1435
APPLICATIONS
Topside MOSFET Driver Supply (C
An external bootstrap capacitor C
pin supplies the gate drive voltage for the topside MOSFET.
Capacitor C
diode D
topside MOSFET is to be turned on, the driver places the
C
enhances the MOSFET and turns on the topside switch.
The switch node voltage SW rises to V
rises to V
needs to be 100 times greater than the total input capaci-
tance of the topside MOSFET. In most applications 0.1 F
is adequate. The reverse breakdown on D
than V
Output Voltage Programming
The output voltage is set by a resistive divider according
to the following formula:
The external resistor divider is connected to the output as
shown in Figure 5 allowing remote voltage sensing.
Run/ Soft Start Function
The RUN/SS pin is a dual purpose pin which provides the
soft start function and a means to shut down the LTC1435.
12
B
V
voltage across the gate source of the MOSFET. This
OUT
IN(MAX).
B
Figure 4b. Capacitive Charge Pump for EXTV
IN
EXTV
from INTV
1 19
B
LTC1435
+ INTV
.
CC
in the Functional Diagram is charged through
V
PGND
V
SW
TG
BG
IN
CC
+
1
U
CC
. The value of the boost capacitor C
R
C
when the SW pin is low. When the
R
IN
2
1
INFORMATION
U
N-CH
N-CH
V
IN
BAT85
B
L1
connected to the Boost
W
B
, D
VN2222LL
IN
0.22 F
B
and the Boost pin
R
B
LTC1435 • F04b
)
SENSE
must be greater
+
+
U
CC
BAT85
BAT85
V
1 F
C
OUT
OUT
B
Soft start reduces surge currents from V
increasing the internal current limit. Power supply se-
quencing can also be accomplished using this pin.
An internal 3 A current source charges up an external
capacitor C
the LTC1435 begins operating. As the voltage on RUN/SS
continues to ramp from 1.3V to 2.4V, the internal current
limit is also ramped at a proportional linear rate. The
current limit begins at approximately 50mV/R
V
2.7V). The output current thus ramps up slowly, charging
the output capacitor. If RUN/SS has been pulled all the way
to ground there is a delay before starting of approximately
500ms/ F, followed by an additional 500ms/ F to reach
full current.
Pulling the RUN/SS pin below 1.3V puts the LTC1435 into
a low quiescent current shutdown (I
can be driven directly from logic as shown in Figure 6.
Diode D1 in Figure 6 reduces the start delay but allows
C
diode and C
The RUN/SS pin has an internal 6V Zener clamp (See
Functional Diagram).
RUN/SS
SS
t
DELAY
to ramp up slowly for the soft start function; this
3.3V OR 5V
Figure 5. Setting the LTC1435 Output Voltage
= 1.3V) and ends at 150mV/R
= 5(10
SS.
SS
Figure 6. RUN/SS Pin Interfacing
When the voltage on RUN/SS reaches 1.3V
D1
can be deleted if soft start is not needed.
LTC1435
5
)C
RUN/SS
V
OSENSE
SS
SGND
Seconds
C
SS
1.19V V
100pF
Q
OUT
< 25 A). This pin
R2
R1
SENSE
LTC1435 • F05
IN
9V
RUN/SS
LTC1435 • F06
by gradually
(V
SENSE
C
RUN/SS
SS
(at
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