LTM4600 LINER [Linear Technology], LTM4600 Datasheet - Page 9

• Manufacturer Part Number: LTM4600
• Description: 10A High Effi ciency DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
The typical LTM4600 application circuit is shown in Figure
17. External component selection is primarily determined
by the maximum load current and output voltage.
Output Voltage Programming and Margining
The PWM controller of the LTM4600 has an internal
0.6V±1% reference voltage. As shown in the block diagram,
a 100k/0.5% internal feedback resistor connects V
FB pins. Adding a resistor R
pin programs the output voltage:
Table 1 shows the standard vaules of 1% R
for typical output voltages:
Table 1.
Voltage margining is the dynamic adjustment of the output
voltage to its worst case operating range in production
testing to stress the load circuitry, verify control/protec-
tion functionality of the board and improve the system
reliability. Figure 2 shows how to implement margining
function with the LTM4600. In addition to the feedback
resistor R
Turn off both transistor Q
margining. When Q
voltage is margined up. The output voltage is margined
R
(kΩ)
(V)
V
SET
O
V
O
=
Open
LTM4600
0.6
0 6
PGND
.
SET
V
, several external components are added.
•
100
1.2
100
R
k R
U
UP
SET
66.5
100k
+
1.5
SGND
is on and Q
SET
Figure 2.
U
49.9
UP
1.8
V
V
SET
OUT
OSET
and Q
from V
43.2
R
2
DOWN
SET
W
DOWN
OSET
31.6
2.5
is off, the output
R
R
DOWN
2N7002
UP
2N7002
to disable the
4600 F02
pin to SGND
Q
Q
SET
22.1
DOWN
UP
3.3
U
resistor
OUT
13.7
and
5
down when Q
voltage V
resistor values of R
the following equations:
Input Capacitors
The LTM4600 µModule should be connected to a low
ac-impedance DC source. High frequency, low ESR input
capacitors are required to be placed adjacent to the mod-
ule. In Figure 20, the bulk input capacitor C
for its ability to handle the large RMS current into the
converter. For a buck converter, the switching duty-cycle
can be estimated as:
Without considering the inductor current ripple, the RMS
current of the input capacitor can be estimated as:
In the above equation, η% is the estimated effi ciency of
the power module. C1 can be a switcher-rated electrolytic
aluminum capacitor, OS-CON capacitor or high volume
ceramic capacitors. Note the capacitor ripple current
ratings are often based on only 2000 hours of life. This
makes it advisable to properly derate the input capacitor,
or choose a capacitor rated at a higher temperature than
required. Always contact the capacitor manufacturer for
derating requirements.
In Figure 16, the input capacitors are used as high fre-
quency input decoupling capacitors. In a typical 10A
output application, 1-2 pieces of very low ESR X5R or
X7R, 10µF ceramic capacitors are recommended. This
decoupling capacitor should be placed directly adjacent
D
I
R
(
CIN RMS
R
SET
=
SET
R
(
R
(
SET
V
SET
V
IN
+
O
O
R
(
•
needs to be margined up/down by ±M%, the
UP
100
)
R
V
=
O
UP
)•
DOWN
I
k R
•( – %)
O MAX
V
)
Ω
1
(
η
O
+
%
UP
•(
100
M
DOWN
is on and Q
1
)
and R
+
•
k
M
Ω
%)
D
)
DOWN
•(
=
1
=
0 6
−
.
0 6
D
UP
.
V
can be calculated from
)
V
is off. If the output
LTM4600
IN
is selected
4600fa
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