ltc3440 Linear Technology Corporation, ltc3440 Datasheet - Page 11

• Manufacturer Part Number: ltc3440
• Description: Micropower Synchronous Buck-boost Dc/dc Converter
• Manufacturer: Linear Technology Corporation

OPERATIO
MULTIPLE
SOFT-START
The soft-start function is combined with shutdown. When
the SHDN/SS pin is brought above typically 1V, the IC is
enabled but the EA duty cycle is clamped from the V
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace Area at FB and V
Low. Lead Length to Battery Should be Kept Short
VIAS
L1
D1
COMPARATORS
GND
TO PWM
1
2
3
4
5
U
R
MODE/SYNC
SW1
GND
T
U
SW2
LTC3440
V
CI
U
D2
C2
SOFT-START
SHDN/SS
CLAMP
V
V
IN
OUT
V
V
FB
IN
V
C
W
OUT
10
9
8
7
6
C1
C
Pins are Kept
ENABLE
R1
Figure 5. Soft-Start Circuitry
U
CHIP
V
IN
C
R2
15μA
pin.
3440 F06
A detailed diagram of this function is shown in Figure 5.
The components R
voltage on the SHDN/SS pin to provide a soft-start
function.
Inductor Selection
The high frequency operation of the LTC3440 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
where f = operating frequency, MHz
L
L
+
–
+
–
>
>
ERROR AMP
f I
f I
V
•
•
IN MIN
1.22V
1V
OUT MAX
V
OUT MAX
(
OUT
(
(
SHDN/SS
)
•
V
10
•
FB
9
8
C
(
(
V
)
)
V
IN MAX
C
SS
•
•
P1
OUT
(
Ripple V
Ripple V
and C
–
C
)
V
SS
V
OUT
–
IN MIN
R
•
•
R1
R2
SS
SS
V
(
OUT
IN MAX
OUT
provide a slow ramping
(
)
)
)
ENABLE SIGNAL
μ
)
H
μ
,
H
LTC3440
3440 F05
11
3440fb