LTC1530CS8 Linear Technology, LTC1530CS8 Datasheet - Page 10

• Manufacturer Part Number: LTC1530CS8
• Description: IC SW REG CNTRLR SYNC ADJ 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1530CS8

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 20A
• Frequency - Switching: 300kHz
• Voltage - Input: 3.3V, 5V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
LTC1530
Figure 5b plots the minimum required R
versus the maximum operating load current (I
I
during an intial power-up sequence (V
inductor’s start-up current I
steady-state condition, I
and I
the input and output voltages, the LTC1530 soft-start slew
rate, the maximum duty cycle and the inductor and output
capacitor values.
For a given application, the input and output requirements
are known and determine the main inductor and output
capacitor values. These values establish the transient load
recovery time. In general, a low value inductor combined
with high value output capacitance has a short transient
load recovery time at the expense of higher inductor ripple
and start-up current (I
inductor and large value output capacitors are chosen, the
value of R
to allow proper regulator start-up.
During start-up, if I
threshold set by the R
limit comparator turns on. This comparator then limits
input charging current by reducing duty cycle. During this
time, if V
value, the LTC1530 hard current limit circuit turns on. This
circuit forces the LTC1530 to repeat a soft-start cycle and
the power supply fails to start. If V
one-half of the rated value, the power supply output may
start-up properly depending on whether the limited input
current charges the output capacitor and prevents hard
current limit action.
Therefore, select R
mind. Choosing R
threshold above I
as well as recovery from an output fault condition.
Figures 6a and 6b plot the start-up I
tance and inductance for unloaded and loaded conditions
with the current limit circuit disabled. Figures 6a and 6b
are provided as examples. Actual I
ditions must be measured for any application circuit so
that R
10
LOAD
LMAX
+ I
IMAX
RIPPLE
OUT
IMAX
is affected by the input power supply slew rate,
can be properly chosen.
doesn’t increase above one-half of the rated
/2) as a function of Q1’s R
obtained from Figure 5b may be too small
ST
IMAX
U
IMAX
ensures proper power supply start-up
ST
RIPPLE
IMAX
is higher than the current limit
LMAX
with the start-up current (I
to set the current comparator
U
resistor, the LTC1530 current
ST
and I
. The difference between I
is much higher than the
ST
ST
W
). However, if a small
OUT
ST
under start-up con-
IMAX
vs output capaci-
DS(ON)
increases above
OUT
resistor (k )
= 0V), the
U
. Note that
LMAX
ST
) in
ST
=
Figure 6a. Start-Up I
Figure 5b. Minimum Required R
Figure 6b. Start-Up I
5500
4500
3500
2500
1500
500
25
20
15
10
30
25
20
15
10
5
0
5
0
0
0
0
T
V
I
T
V
I
LOAD
LOAD
R
I
A
IN
A
IN
LMAX
IMAX
2
= 25 C
= 25 C
= 5V
= 5V
2
2
= 0A
= 10A
OUTPUT CAPACITANCE (mF)
OUTPUT CAPACITANCE (mF)
= I
4
500
LOAD
6
4
4
Q1 R
+ I
8
I
RIPPLE
ST
LMAX
DS(ON)
ST
L = 1.2 H
L = 4.7 H
6
10
6
vs Output Capacitance
vs Output Capacitance
(A)
/2
L = 2.4 H
L = 1.2 H
= 0.05
12
8
8
L = 2.4 H
14
L = 4.7 H
IMAX
16 18
10
10
0.03
0.02
0.01
0.04
1530 F06a
1530 F06b
1530 F05b
vs I
12
12
20
LMAX
1530fa