Datasheet

LTM8023
12
8023fj
For more information www.linear.com/LTM8023
APPLICATIONS INFORMATION
Load Sharing
Two or more LTM8023’s may be paralleled to produce
higher currents. To do this, tie the V
IN
, ADJ, V
OUT
and
SHARE pins of all the paralleled LTM8023’s together. To
ensure that paralleled modules start up together, the RUN/
SS pins may be tied together, as well. If the RUN/SS pins
are not tied together, make sure that the same valued soft-
start capacitors are used for each module. An example
of two LTM8023 modules configured for load sharing is
given in the Typical Applications section.
For current sharing applications using multiple LTM8023s,
the ADJ pins for all regulators may be combined using
one resistor to ground as determined by:
R
ADJ
=
394.21
N
V
OUT
– 0.79
where N is the number of paralleled modules and R
ADJ
is in kΩ.
Burst Mode Operation
To enhance efficiency at light loads, the LTM8023 auto-
matically switches to Burst Mode operation which keeps
the output capacitor charged to the proper voltage while
minimizing the input quiescent current. During Burst Mode
operation, the LTM8023 delivers single cycle bursts of
current to the output capacitor followed by sleep periods
where the output power is delivered to the load by the output
capacitor. In addition, V
IN
and BIAS quiescent currents are
reduced to typically 25µA and 50µA respectively during
the sleep time. As the load current decreases towards a no
load condition, the percentage of time that the LTM8023
operates in sleep mode increases and the average input
current is greatly reduced, resulting in higher efficiency.
Burst Mode operation is enabled by tying SYNC to GND.
To disable Burst Mode operation, tie SYNC to a stable
voltage above 0.7V or synchronize to an external clock.
Do not leave the SYNC pin floating .
Minimum Input Voltage
The LTM8023 is a step-down converter, so a minimum
amount of headroom is required to keep the output in
regulation. In addition, the input voltage required to turn
on is higher than that required to run, and depends upon
whether the RUN/SS is used. As shown in Figure 2, it
takes only about 3.5V
IN
for the LTM8023 to run a 3.3V
output at light load. If RUN/SS is tied to V
IN
, a 5.5V input
voltage is required to start. If V
IN
is allowed to settle in
the operating region first then the RUN/SS pin is enabled,
the minimum input voltage to start at light load is lower,
about 4
.2V. A similar curve for 5V
OUT
operation is also
provided in Figure 2.
Figure 2. The LTM8023 Needs More Voltage to Start Than to Run
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
8023 F02
LOAD CURRENT (mA)
0
INPUT VOLTAGE (V)
4.0
4.5
5.0
2000
3.5
3.0
500 1000 1500
0 2000500 1000 1500
6.0
5.5
TO START
RUN/SS ENABLED
TO RUN
TO START
RUN/SS ENABLED
TO RUN
V
OUT
= 3.3V
T
A
= 25°C
f = 650kHz
6.5
7.0
6.0
5.0
5.5
7.5
V
OUT
= 5V
T
A
= 25°C
f = 650kHz
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