Datasheet

[sec]+
)7.- 0V(xC
=t
INOUT
SS
I
CHARGE_INIT
I
CHARGE_SS
VxC
FBS
V
EN
appropriate V
OUT
Linear Charging
Period
V
SS
= V
FB
V
OUT
= V
IN
- 0.7V
V
SS
Shutdown
Soft-Start
Switching Period
Normal Switching
Operation
V
SS
= V
IN
V
OUT
LM4510
SNVS533C –SEPTEMBER 2007–REVISED MAY 2013 www.ti.com
Table 3. Suggested C
IN
and C
OUT
Capacitors and Their Suppliers
Case Size
Model Type Vendor Voltage Rating
Inch (mm)
4.7 µF for C
IN
C2012X5R0J475 Ceramic, X5R TDK 6.3V 0805 (2012)
GRM21BR60J475 Ceramic, X5R muRata 6.3V 0805 (2012)
JMK212BJ475 Ceramic, X5R Taiyo-Yuden 6.3V 0805 (2012)
C2012X5R0J475K Ceramic, X5R TDK 6.3V 0603 (1608)
10 µF for C
OUT
TMK316BJ106KL Ceramic, X5R Taiyo-Yuden 25V 1206 (3216)
12103D106KAT2A Ceramic, X5R AVX 25V 1210 (3225)
SOFT-START FUNCTION AND SOFT-START CAPACITOR SELECTION
The LM4510 has a soft-start pin that can be used to limit the input inrush current. Connect a capacitor from SS
pin to GND to set the soft-start period. Figure 27 describes the soft start process.
• Initial charging period: When the device is turned on, the control circuitry linearly regulating initial charge
current charges V
OUT
by limiting the inrush current.
• Soft-start period: After V
OUT
reaches V
IN
-0.7V (typ.), the device starts switching and the C
S
is charged at a
constant current of 11 μA, ramping up to V
IN
. This period ends when V
SS
reaches V
FB
. C
S
should be large
enough to ensure soft-start period ends after C
O
is fully charged.
During the initial charging period, the required load current must be smaller than the initial charge current to
ensure V
OUT
reaches V
IN
-0.7V (typ.).
Figure 27. Soft Start Timing Diagram
C
S
Selection
The soft-start time without load can be estimated as:
(8)
Where the I
INIT_CHARGE
is Initial Charging Current depending on V
IN
and I
SS_CHARGE
(11 μA (typ.)). Also, when
selecting the fuse current rating, make sure the value is higher than the initial charging current.
COMPENSATION COMPONENT SELECTION
The LM4510 provides a compensation pin COMP to customize the voltage loop feedback. It is recommended
that a series combination of R
C
and C
C1
be used for the compensation network, as shown in the typical
application circuit. In addition, C
C2
is used for compensating high frequency zeros.
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