LSN-10A D12 Models
Single Output, Non-Isolated, 12VIN, 1-5VOUT, 10A, DC/DC's in SIP Packages
elements and should be selected for bulk capacitance, low ESR, and appro-
Remote Sense
priate frequency response. Any scope measurements of PARD should be
made directly at the DC/DC output pins with scope probe ground less than
0.5" in length.
LSN D1ꢁ SIP Series DC/DC converters offer an output sense function on
pin 3. The sense function enables point-of-use regulation for overcoming
moderate IR drops in conductors and/or cabling. Since these are non-isolated
devices whose inputs and outputs usually share the same ground plane,
sense is provided only for the +Output.
All external capacitors should have appropriate voltage ratings and be located
as close to the converters as possible. Temperature variations for all relevant
parameters should be taken into consideration.
The remote sense line is part of the feedback control loop regulating the
DC/DC converter’s output. The sense line carries very little current and
consequently requires a minimal cross-sectional-area conductor. As such, it
is not a low-impedance point and must be treated with care in layout and
cabling. Sense lines should be run adjacent to signals (preferably ground),
and in cable and/or discrete-wiring applications, twisted-pair or similar tech-
niques should be used. To prevent high frequency voltage differences between
VOUT and Sense, we recommend installation of a 1000pF capacitor close to
the converter.
The most effective combination of external I/O capacitors will be a function
of your line voltage and source impedance, as well as your particular load and
layout conditions. Our Applications Engineers can recommend potential solu-
tions and discuss the possibility of our modifying a given device’s internal filter-
ing to meet your specific requirements. Contact our Applications Engineering
Group for additional details.
Input Fusing
Most applications and or safety agencies require the installation of fuses
at the inputs of power conversion components. LSN D1ꢁ Series DC/DC
converters are not internally fused. Therefore, if input fusing is mandatory,
either a normal-blow or a slow-blow fuse with a value no greater than 9 Amps
should be installed within the ungrounded input path to the converter.
The sense function is capable of compensating for voltage drops between the
+Output and +Sense pins that do not exceed 10ꢀ of VOUT.
[VOUT(+) – Common] – [Sense(+) – Common] b 10ꢀVOUT
Power derating (output current limiting) is based upon maximum output cur-
rent and voltage at the converter's output pins. Use of trim and sense func-
tions can cause the output voltage to increase, thereby increasing output
power beyond the LSN's specified rating. Therefore:
As a rule of thumb however, we recommend to use a normal-blow or slow-
blow fuse with a typical value of about twice the maximum input current,
calculated at low line with the converters minimum efficiency.
(VOUT at pins) x (IOUT) b rated output power
Safety Considerations
The internal 10.57 resistor between +Sense and +Output (see Figure 1)
serves to protect the sense function by limiting the output current flowing
through the sense line if the main output is disconnected. It also prevents
output voltage runaway if the sense connection is disconnected.
LSN D1ꢁ SIP's are non-isolated DC/DC converters. In general, all DC/DC's
must be installed, including considerations for I/O voltages and spacing/
separation requirements, in compliance with relevant safety-agency speci-
fications (usually UL/IEC/EN60950).
Note: Connect the +Sense pin (pin 3) to +Output (pin 4) at the DC/DC
converter pins, if the sense function is not used for remote regulation.
In particular, for a non-isolated converter's output voltage to meet SELV
(safety extra low voltage) requirements, its input must be SELV compliant.
If the output needs to be ELV (extra low voltage), the input must be ELV.
On/Off Control and Power-up Sequencing
Input Overvoltage and Reverse-Polarity Protection
The On/Off Control pin may be used for remote on/off operation. LSN D1ꢁ SIP
Series DC/DC's are designed so they are enabled when the control pin is
left open (internal pull-down to Common) and disabled when the control pin is
pulled high (+ꢁ.8V to +VIN), as shown in Figure ꢁ and ꢁa.
LSN D1ꢁ SIP Series DC/DC's do not incorporate either input overvoltage
or input reverse-polarity protection. Input voltages in excess of the specified
absolute maximum ratings and input polarity reversals of longer than "instan-
taneous" duration can cause permanent damage to these devices.
Dynamic control of the on/off function is best accomplished with a mechanical
relay or open-collector/open-drain drive circuit. The drive circuit should be
able to sink appropriate current when activated and withstand appropriate
voltage when deactivated.
Start-Up Time
The VIN to VOUT Start-Up Time is the interval between the time at which a
ramping input voltage crosses the lower limit of the specified input voltage
range (10.8 Volts) and the fully loaded output voltage enters and remains
within its specified accuracy band. Actual measured times will vary with input
source impedance, external input capacitance, and the slew rate and final
value of the input voltage as it appears to the converter.
+INPUT
10k7
4.12k7
ON/OFF
CONTROL
1.62k7
The On/Off to VOUT Start-Up Time assumes the converter is turned off via the
On/Off Control with the nominal input voltage already applied to the converter.
The specification defines the interval between the time at which the converter
is turned on and the fully loaded output voltage enters and remains within its
specified accuracy band. See Typical Performance Curves.
COMMON
Figure 2. Driving the On/Off Control Pin with an Open-Collector Drive Circuit
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