LTC1622IS8#TR Linear Technology, LTC1622IS8#TR Datasheet - Page 12

• Manufacturer Part Number: LTC1622IS8#TR
• Description: IC CTRLR DC/DC STEP DOWN 8SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1622IS8#TR

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 110kHz ~ 550kHz
• Voltage - Input: 2 ~ 10 V
• Operating Temperature: -45°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LTC1622
down to 2.7V. Let’s assume that the MOSFET dissipation
is to be limited to P
is 50 C/W. Hence the junction temperature at T
will be 37.5 C and p = 0.005 (37.5 – 25) = 0.0625. The
required R
The P-channel MOSFET requirement can be met by an
Si6433DQ.
The requirement for the Schottky diode is the most strin-
gent when V
R
Schottky is 0.1/0.025 = 4A. An MBRS340T3 Schottky
diode is chosen. With 4A flowing through, the diode is
rated with a forward voltage of 0.4V. Therefore, the worst-
case power dissipated by the diode is 1.6W. The addition
of D
approximately 0.8W.
The input capacitor requires an RMS current rating of at
least 0.75A at temperature, and C
of 0.1 for optimum efficiency.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1622. These items are illustrated graphically in the
12
APPLICATIONS
SENSE
R
DS ON
FB
(Figure 5) will reduce the diode dissipation to
resistor, the short-circuit current through the
DS(ON)
OUT
DC I
= 0V, i.e., short circuit. With a 0.025
is then given by:
OUT
P
U
= 250mW and its thermal resistance
P
P
2
BOLD LINES INDICATE HIGH CURRENT PATHS
R
INFORMATION
1
ITH
C
R1
U
ITH
Figure 6. LTC1622 Layout Diagram (See PC Board Layout Checklist)
p
R2
OUT
0 11
W
C1
will require an ESR
1
2
3
4
C
SS
SENSE
I
V
RUN/
SS
TH
FB
QUIET SGND
LTC1622
–
U
A
SYNC/
MODE
= 25 C
PDRV
GND
V
IN
8
7
6
5
layout diagram in Figure 6. Check the following in your
layout:
1. Is the Schottky diode closely connected between ground
2. Does the (+) plate of C
3. Is the input decoupling capacitor (0.1 F) connected
4. Connect the end of R
5. Is the trace from the SENSE
6. Keep the switching node, SW, away from sensitive
7. Does the V
0.1 F
at (–) lead of C
as closely as possible? This capacitor provides AC
current to the MOSFET.
closely between V
possible. The V
comparator.
resistor kept short? Does the trace connect close to
R
small signal nodes.
resistors? The resistive divider R1 and R2 must be
connected between the (+) plate of C
ground. Optional capacitor C1 should be located as
close as possible to the LTC1622.
R1 and R2 should be located as close as possible to the
LTC1622. R2 should connect to the output as close to
the load as practicable.
SENSE
M1
SW
R
?
SENSE
FB
+
IN
pin connect directly to the feedback
IN
C
IN
and drain of the external MOSFET?
L1
IN
pin is the SENSE
(Pin 8) and ground (Pin 6)?
SENSE
IN
1622 F06
+
connect to the sense resistor
C
as close to V
OUT
V
V
IN
OUT
–
(Pin 1) to the Sense
+
OUT
of the current
IN
and signal
(Pin 8) as