Linear Technology LTM4611EV Demo Board, 1.5V ≤ VIN ≤ 5.5V, VOUT = 0.8V to 5V @ 15A, DC/DC µModule Regulator DC1588A DC1588A 데이터 시트
제품 코드
DC1588A
LTM4611
11
4611fb
The typical LTM4611 application circuit is shown in
Figure 21. External component selection is primarily
determined by the maximum load current and output
voltage. Refer to Table 5 for specific external capacitor
requirements for particular applications.
V
IN
to V
OUT
Step-Down Ratios
There are restrictions in the V
IN
to V
OUT
step-down
ratio that can be achieved for a given input voltage. The
V
IN
to V
OUT
minimum dropout is still a function of its load
current at very low input voltages. A dropout voltage of
300mV from input to output of LTM4611 is achievable
at 15A load, but reflected input voltage ripple and noise
should be taken into consideration in such applications.
Additionally, the transient-handling capability of the source
supply feeding LTM4611 can become an important factor
in truly achieving ultralow dropout at high output current.
For example, V
IN
can sag or overshoot dramatically when
LTM4611 responds to heavy transient step loads on its
output, if insufficient input bypass capacitance is used in
combination with a sluggish source supply.
When V
When V
OUT
is expected to be within 600mV of V
IN
, or
when the caliber of the source supply is in question, it
is recommended to evaluate the amount and quality of
input bypass capacitance needed to maintain one’s target
dropout voltage with the source supply that will be used
in the end application. Demo Board DC1588A can be used
for such evaluation.
At very low duty cycles the minimum specified on-time
At very low duty cycles the minimum specified on-time
must be maintained. See the Frequency Adjustment sec-
tion and temperature derating curves.
To prevent overstress to the µpower bias generator, do
To prevent overstress to the µpower bias generator, do
not ramp up V
IN
at a rate exceeding 5V/µs (in practice, it
is difficult to violate this guideline.) There is no restriction
on how rapidly V
IN
may be discharged.
Output Voltage Programming
The PWM controller has an internal 0.8V ±1.75% reference
The PWM controller has an internal 0.8V ±1.75% reference
voltage over temperature. As shown in the Block Diagram,
a 60.4k internal feedback resistor connects the V
OUT_LCL
and V
FB
pins together. When the remote sense amplifier
applicaTions inForMaTion
is used, then DIFFV
OUT
is connected to the V
OUT_LCL
pin.
If the remote sense amplifier is not used, then V
OUT_LCL
connects to V
OUT
. The output voltage will default to 0.8V
with no feedback resistor. Adding a resistor R
FB
from V
FB
to GND programs the output voltage:
V
OUT
= 0.8V •
60.4k + R
FB
R
FB
Table 1. V
FB
Resistor Table vs Various Output Voltages
V
OUT
0.8V
1.0V
1.2V
1.5V
1.8V
2.5V 3.3V
5.0V
R
FB
(kΩ) Open
243
121
68.1
47.5
28.0
19.1
11.5
For parallel operation of N LTM4611s, the following equa-
tion can be used to solve for R
FB
:
R
FB
=
60.4k / N
V
OUT
0.8V
– 1
Tie the V
FB
pins together for each parallel output. The
COMP, TRACK/SS, V
OUT_LCL
, and RUN pins must also be
tied together as shown in Figures 18 and 19.
For parallel applications, best noise immunity can be
For parallel applications, best noise immunity can be
achieved by placing capacitors of value C
P
from V
FB
to GND,
and value C
FF
from V
OUT
to V
FB
, local to each µModule.
If space limitations impede realizing this, then placement
of capacitors of value N • C
P
from V
FB
to GND, and value
N • C
FF
from V
OUT
to the bussed V
FB
signal, can suffice.
Input Capacitors
The LTM4611 module should be connected to a low
The LTM4611 module should be connected to a low
AC impedance DC source. Additional input capacitors
are needed for the RMS input ripple current rating. The
I
CIN(RMS)
equation which follows can be used to calculate
the input capacitor requirement. Typically 22µF X7R ce-
ramics are a good choice with RMS ripple current ratings
of ~2A each. A 100µF to 150µF surface mount aluminum
electrolytic bulk capacitor can be used for more input
bulk capacitance. This bulk input capacitor is only needed
if the input source impedance is compromised by long
inductive leads, traces or not enough source capacitance.
If low impedance power planes are used, then this bulk
capacitor is not needed.