LTM4623
15
4623fc
For more information www.linear.com/LTM4623
applicaTions inForMaTion
RUN Enable
Pulling the RUN pin to ground forces the LTM4623 into
its shutdown state, turning off both power MOSFETs and
most of its internal control circuitry. Bringing the RUN pin
above 0.7V turns on the internal reference only, while still
keeping the power MOSFETs off. Increasing the RUN pin
voltage above 1.2V will turn on the entire chip.
Low Input Application
The LTM4623 module has a separate SV
IN
pin which makes
it suitable for low input voltage applications down to 2.375V.
The SV
IN
pin is the single input of the whole control circuitry
while the V
IN
pin is the power input which directly connects
to the drain of the top MOSFET. In most applications where
V
IN
is greater than 4V, connect SV
IN
directly to V
IN
with a
short trace. An optional filter, consisting of a resistor (1Ω
to 10Ω) between SV
IN
and V
IN
along with a 0.1µF bypass
capacitor between SV
IN
and ground, can be placed for
additional noise immunity. This filter is not necessary in
most cases if good PCB layout practices are followed (see
Figure 23). In a low input voltage application (2.375V to
4V), connect SV
IN
to an external voltage higher than 4V
with 1µF local bypass capacitor. See Operating Frequency
section. Figure 25 shows an example of a low input voltage
application. Please note the SV
IN
voltage cannot go below
the V
OUT
voltage.
Pre-Biased Output Start-Up
There may be situations that require the power supply to
start up with a pre-bias on the output capacitors. In this
case, it is desirable to start up without discharging that
output pre-bias. The LTM4623 can safely power up into
a pre-biased output without discharging it.
The LTM4623 accomplishes this by forcing discontinuous
mode (DCM) operation until the TRACK/SS pin voltage
reaches 0.6V reference voltage. This will prevent the BG
from turning on during the pre-biased output start-up
which would discharge the output.
Please do not pre-bias LTM4623 with a voltage higher
than INTV
CC
(3.3V) voltage or a voltage higher than the
output voltage set by the feedback resistor (R
FB
).
Overtemperature Protection
The internal overtemperature protection monitors the
junction temperature of the module. If the junction
temperature reaches approximately 160°C, both power
switches will be turned off until the temperature drops
about 15°C cooler.
Radiated EMI Noise
High radiated EMI noise is a disadvantage for switching
regulators by nature. Fast switching turn-on and turn-off
make the large di/dt change in the converters, which act
as the radiation sources in most systems. LTM4623 in
-
tegrates the feature to minimize the radiated EMI noise to
meet the most applications with low noise requirements.
It is fully compliant with the E
N55022 Class B Standard.
Thermal Considerations and Output Current Derating
The thermal resistances reported in the Pin Configuration
section of the data sheet are consistent with those param
-
eters defined by JESD
51-12 and are intended for use with
finite element analysis (FEA) software modeling tools that
leverage the outcome of thermal modeling, simulation,
and correlation to hardware evaluation performed on a
µModule package mounted to a hardware test board.
The motivation for providing these thermal coefficients is
found in JESD 51-12 (Guidelines for Reporting and Using
Electronic Package Thermal Information).
Many designers may opt to use laboratory equipment
and a test vehicle such as the demo board to anticipate
the µModule regulator’s thermal performance in their ap
-
plication at various electrical and environmental operating
conditions to compliment any FEA activities. Without FEA
software, the thermal resistances reported in the Pin Con
-
figuration section are, in and of themselves, not relevant to
providing guidance of thermal per
formance
; instead, the
derating curves provided in this data sheet can be used
in a manner that yields insight and guidance pertaining to
one’s application usage, and can be adapted to correlate
thermal performance to one’s own application.
