LSN-T10-D12J Datasheet, PDF (6/12 Pages) Murata Manufacturing Co., Ltd. – Single Adjustable Output, Non-isolated, 12Vin, 10A, SIP, DC/DC Converters

LSN-T/10-D12
Single Adjustable Output, Non-isolated, 12Vin, 10A, SIP, DC/DC Converters
Pre-Biased Startup
Newer systems with multiple power voltages have an additional problem
besides startup sequencing. Some sections have power already partially ap-
plied (possibly because of earlier power sequencing) or have leakage power
present so that the DC/DC converter must power up into an existing voltage.
This power may either be stored in an external bypass capacitor or supplied
by an active source.
This “pre-biased” condition can also occur with some types of program-
mable logic or because of blocking diode leakage or small currents passed
through forward biased ESD diodes. Conventional DC/DC’s may fail to start up
correctly if there is output voltage already present. And some external circuits
are adversely affected when the low side MOSFET in a synchronous rectifier
converter sinks current at start up.
The LSN2 series includes a pre-bias startup mode to prevent these initializa-
tion problems. Essentially, the converter acts as a simple buck converter until
the output reaches its set point voltage at which time it converts to a synchro-
nous rectifier design. This feature is variously called “monotonic” because
the voltage does not decay (from low side MOSFET shorting) or produce a
negative transient once the input power is applied and the startup sequence
begins.
Output Adjustments
The LSN-T/10-D12J includes an output adjustment and trimming function
which is fully compatible with competitive units. The output voltage may be
varied using a single trim resistor from the Trim input to Power Common or an
external DC trim voltage applied between the Trim input and Power Common.
For resistor trim adjustments, be sure to use a precision low-tempco resistor
(±100 ppm/°C) mounted close to the converter with short leads. Since the
output accuracy is ±2% (typical), you may need to vary this resistance slightly.
For adjustments using an external voltage reference, the equivalent input im-
pedance looking in to the Trim input is approximately 5,000 Ohms. Therefore
you may have to compensate for this in the source resistance of your external
reference. Although filtered internally, the Trim input is sensitive and therefore
susceptible to noise pickup with longer leads. Consider adding a small bypass
capacitor, 0.1μF or larger mounted adjacent to the converter between the Trim
and Power Common if there is noise in the application.
The Trim input voltage range is offset against the 0.7 Volt reference of the
PWM. Also note that the Trim input is inverting (lower trim voltage produces
higher output voltage and vice versa). Do not exceed the voltage range or
maximum power rating.
D12 Models Resistor Trim Equation:
RTRIM (Ω) = ^{_____1_0_5_0__0___} –1000
VO – 0.7525
where VO is the desired output voltage.
VOUT 0.7525V 1.0V 1.2V 1.5V 1.8V 2V 2.5V 3.3V 5V
RTRIM Open 41.424 22.46 13.05 9.024 7.417 5.009 3.122 1.472
(kΩ)
D12 Models Voltage Trim Equation:
VTRIM (in Volts) = 0.7 –(0.0667 x (VO – 0.7525))
where VO is the desired output voltage.
The D12 fixed trim voltages to set the output voltage are:
VOUT 0.7525V 1.0V 1.2V 1.5V 1.8V 2V 2.5V 3.3V 5V
VTRIM Open 0.6835 0.670 0.650 0.630 0.617 0.583 0.530 0.4166
(V)
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Trim Connections

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LSN-T10-D12.B01 Page 6 of 12