LTM4601A LINER [Linear Technology], LTM4601A Datasheet - Page 11

• Manufacturer Part Number: LTM4601A
• Description: Ultralow EMI 28VIN, 6A DC/DC ?Module Regulator
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
The typical LTM4606 application circuit is shown in Fig-
ure 20. External component selection is primarily deter-
mined by the maximum load current and output voltage.
Refer to Table 2 for specific external capacitor requirements
for a particular application.
V
Under the default frequency, there are restrictions in
the maximum V
achieved for a given input voltage. These constraints are
caused by the limitation of the minimum on and off time in
the internal switches. Refer to the Frequency Adjustment
section to change the switching frequency and get wider
input and output ranges. See the Thermal Considerations
and Output Current Derating section in this data sheet for
the current restrictions.
Output Voltage Programming and Margining
The PWM controller has an internal 0.6V reference voltage.
As shown in the Block Diagram, a 60.4k internal feedback
resistor connects the V
a resistor R
the output voltage:
Table 1. R
The MPGM pin programs a current that when multiplied
by an internal 10k resistor sets up the 0.6V reference ±
offset for margining. A 1.18V reference divided by the
(kΩ)
V
R
IN
(V)
OUT
FB
V
to V
OUT
Open
OUT
0.6
= 0.6V
FB
Standard 1% Resistor Values vs V
FB
Step-Down Ratios
from the V
60.4
1.2
IN
60.4k + R
and V
40.2
R
1.5
FB
OUT
FB
OUT
FB
30.1
pin to the SGND pin programs
1.8
and V
step-down ratio that can be
25.5
FB
2
pins together. Adding
19.1
2.5
OUT
13.3
3.3
8.25
5
RPGM resistor on the MPGM pin programs the current.
Calculate V
where %V
margin, and V
where RPGM is the resistor value to place on the MPGM
pin to ground.
The output margining will be ± margining of the value.
This is controlled by the MARG0 and MARG1 pins. See
the truth table below:
Input Capacitors and Input EMI Noise Attenuation
The LTM4606 is designed to achieve low input conducted
EMI noise due to the fast switching of turn-on and turn-off.
In the LTM4606, a high frequency inductor is integrated
to the input line for noise attenuation. V
are available for external input capacitors to form a high
frequency π filter. As shown in Figure 19, the ceramic
capacitor C1 on the V
the RMS current into the converter, so careful attention
is needed for capacitor C1 selection.
For a buck converter, the switching duty cycle can be
estimated as:
R
D =
V
OUT(MARGIN)
PGM
MARG1
HIGH
HIGH
V
LOW
LOW
V
OUT
=
IN
OUT
OUT(MARGIN)
V
0.6V
OUT
OUT(MARGIN)
is the percentage of V
=
•
V
%V
OUT(MARGIN)
100
D
1.18V
:
OUT
pins is used to handle most of
MARG0
HIGH
HIGH
is the margin quantity in volts:
LOW
LOW
• V
OUT
• 10k
LTM4606
OUT
MARGIN DOWN
D
NO MARGIN
MARGIN UP
NO MARGIN
and V
you want to
MODE
11
IN
pins
4606fb