Datasheet

LTM8032
12
8032fg
For more information www.linear.com/LTM8032
applicaTions inForMaTion
than 56V. If BIAS power is applied from a remote or noisy
voltage source, it may be necessary to apply a decoupling
capacitor locally to the LTM8032.
Load Sharing
Tw o or more LTM8032s may be paralleled to produce higher
currents. This may, however, alter the EMI performance
of the LTM8032s. To do this, tie the V
IN
, ADJ, V
OUT
and
SHARE pins of all the paralleled LTM8032s together. To
ensure that paralleled modules start up together, the RUN/
SS pins may be tied together, as well. Synchronize the
LTM8032s to an external clock to eliminate beat frequen
-
cies, if
required. 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 LTM8032
modules configured for load sharing is given in the Typical
Applications section.
For current sharing applications using multiple LTM8032s,
the ADJ pins for all regulators may be combined using
one resistor to ground as determined by:
R
ADJ
=
196.71
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 LTM8032 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 LTM8032 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 60µA respectively during
the sleep time. As the load current decreases towards a
no-load condition, the percentage of time that the LTM8032
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.
Figure 1. The LTM8032 Needs More Voltage to Start Than Run
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 LTM8032 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 1, it
takes only about 3.6V
IN
for the LTM8032 to run a 3.3V
output at light load. If RUN/SS is tied directly 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 4.7V. A similar curve for 5V
OUT
operation
is also provided in Figure 1.
LOAD CURRENT (mA)
0
3.0
INPUT VOLTAGE (V)
3.5
4.0
4.5
5.0
5.5
6.0
500 1000 1500 2000
8032 F01a
TO RUN
TO START
RUN/SS ENABLED
V
OUT
= 3.3V
LOAD CURRENT (mA)
0
INPUT VOLTAGE (V)
6.5
7.0
7.5
8032 F01b
6.0
5.5
5.0
500
1000
1500
2000
TO RUN
TO START
RUN/SS ENABLED
V
OUT
= 5V