LTC1530C Linear Technology, LTC1530C Datasheet - Page 10

• Manufacturer Part Number: LTC1530C
• Description: High Power Synchronous Switching Regulator Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC1530
Figure 5b is derived based on the condition that
I
minimum R
the initial power-up phase (V
I
I
I
bined with a low value inductor increases the start-up
I
capacitance and inductance for unloaded and loaded con-
ditions with the current limit circuit disabled. Figures 6a
and 6b are provided as examples. Actual I
start-up conditions must be measured for any application
circuit so that R
In order for the current limit circuit to operate properly and
to obtain a reasonably accurate current limit threshold, the
I
source pins. A 0.1 F decoupling capacitor can also be
connected across R
tion, LTC recommends that the voltage drop across the
R
or ringing at Q1’s source can cause the actual current limit
to be greater than the desired current limit set point.
MOSFET Gate Drive
The PV
voltage, V
efficient operation. This higher voltage can be supplied
with a separate supply, or it can be generated using a
simple charge pump as shown in Figure 7. The 86%
maximum duty cycle ensures sufficient off-time to refresh
the charge pump during each cycle.
As PV
lockout circuit prevents G1 and G2 from pulling high until
PV
from triggering the current limit comparator while PV
slewing, the current limit circuit is disabled until PV
shutdown, the driver logic is designed to hold G2 low until
G1 first goes high.
10
LMAX
LMAX
LMAX
LMAX
LMAX
MAX
IMAX
8V. In addition, on start-up or recovery from thermal
CC
and I
. Therefore, R
. Figures 6a and 6b plot the start-up I
CC
reaches about 3.5V. To prevent Q1’s high R
can be much higher than the steady state condition
= I
in mind. In general, high output capacitance com-
resistor be set to 100mV. Otherwise, noise spikes
CC
is powered up from 0V, the LTC1530 undervoltage
LOAD
FB
IN
supply must be greater than the input supply
IMAX
, by at least one power MOSFET V
pins must be Kelvin sensed at Q1’s drain and
+ I
IMAX
value. It must be understood that during
RIPPLE
IMAX
U
IMAX
can be properly chosen.
/2. Therefore, it only provides the
must be selected with the start-up
to filter switching noise. In addi-
U
OUT
= 0V), the initial start-up
W
LMAX
LMAX
U
GS(ON)
vs output
DS(ON)
under
CC
CC
for
is
is
Figure 6a. Start-Up I
Figure 6b. Start-Up I
Figure 5b. Minimum Required R
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
R
I
LOAD
T
V
I
LMAX
A
IN
LOAD
A
IMAX
2
IN
= 25 C
= 25 C
= 5V
= 5V
2
2
= 0A
= I
4
OUTPUT CAPACITANCE (mF)
= 10A
OUTPUT CAPACITANCE (mF)
500
LOAD
6
4
Q1 R
4
+ I
LMAX
8
LMAX
I
RIPPLE
LMAX
DS(ON)
10
6
L = 1.2 H
L = 4.7 H
6
vs Output Capacitance
(A)
vs Output Capacitance
/2
= 0.05
12
L = 2.4 H
L = 1.2 H
8
8
14
L = 2.4 H
L = 4.7 H
IMAX
16 18
10
10
0.03
0.02
0.01
0.04
1530 F06a
1530 F05b
1530 F06b
vs I
20
12
12
LMAX