LSN2-T30-D12 Datasheet, PDF (6/17 Pages) Murata Manufacturing Co., Ltd. – DOSA-SIP, 30A POL DC/DC Converters

LSN2-T/30-D12 Series
DOSA-SIP, 30A POL DC/DC Converters
Power-up Sequencing
If a controlled start-up of one or more LSN2-T/30-D12 Series DC/DC converters
is required, or if several output voltages need to be powered-up in a given
sequence, the On/Off control pin can be driven with an external open collector
device as per Figure 4.
Output Overvoltage Protection
LSN2-T/30-D12 SIP Series DC/DC converters do not incorporate output
overvoltage protection. In the extremely rare situation in which the device’s
feedback loop is broken, the output voltage may run to excessively high levels
(VOUT = VIN). If it is absolutely imperative that you protect your load against
+INPUT
continuously attempt to restart itself, go into overcurrent, and then shut down.
Once the output short is removed, the converter will automatically restart itself.
Output Reverse Conduction
Many DC/DCs using synchronous rectification suffer from Output Reverse
Conduction. If those devices have a voltage applied across their output before
a voltage is applied to their input (this typically occurs when another power
supply starts before them in a power-sequenced application), they will either
fail to start or self destruct. In both cases, the cause is the “freewheeling” or
“catch” FET biasing itself on and effectively becoming a short circuit.
LSN2-T/30-D12 SIP DC/DC converters do not suffer from Output Reverse
Conduction. They employ proprietary gate drive circuitry that makes them
immune to moderate applied output overvoltages.
SMALL
SIGNAL
TRANSISTOR
HI = ON
LO = OFF
ON/OFF
CONTROL
SIGNAL
GROUND
+V
SHUTDOWN
CONTROLLER
Thermal Considerations and Thermal Protection
The typical output-current thermal-derating curves shown below enable
designers to determine how much current they can reliably derive from each
model of the LSN2-T/30-D12 SIPs under known ambient-temperature and air-
flow conditions. Similarly, the curves indicate how much air flow is required to
reliably deliver a specific output current at known temperatures.
COMMON
Figure 4. On/Off Control Using An External Open Collector Driver
any and all possible overvoltage situations, voltage limiting circuitry must be
provided external to the power converter.
Output Overcurrent Detection
Overloading the power converter’s output for an extended time will invariably
cause internal component temperatures to exceed their maximum ratings
and eventually lead to component failure. High-current-carrying components
such as inductors, FET’s and diodes are at the highest risk. LSN2-T/30-D12
SIP Series DC/DC converters incorporate an output overcurrent detection and
shutdown function that serves to protect both the power converter and its load.
If the output current exceeds it maximum rating by typically 50% or if the
output voltage drops to less than 98% of it original value, the LSN2-T/30-D12’s
internal overcurrent-detection circuitry immediately turns off the converter,
which then goes into a “hiccup” mode. While hiccupping, the converter will
The highest temperatures in LSN2-T/30-D12 SIPs occur at their output
inductor, whose heat is generated primarily by I²R losses. The derating curves
were developed using thermocouples to monitor the inductor temperature and
varying the load to keep that temperature below +110°C under the assorted
conditions of air flow and air temperature. Once the temperature exceeds
+115°C (approx.), the thermal protection will disable the converter. Automatic
restart occurs after the temperature has dropped below +110°C.
As you may deduce from the derating curves and observe in the efficiency
curves on the following pages, LSN2-T/30-D12 SIPs maintain virtually constant
efficiency from half to full load, and consequently deliver very impressive
temperature performance even if operating at full load.
Lastly, when LSN2-T/30-D12 SIPs are installed in system boards, they are
obviously subject to numerous factors and tolerances not taken into account
here. If you are attempting to extract the most current out of these units under
demanding temperature conditions, we advise you to monitor the output-
inductor temperature to ensure it remains below +110°C at all times.
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MDC_LSN2-T/30-D12 Series.B17 Page 6 of 17