Datasheet

Input Ripple Current and Output Noise
All models in this converter series are tested and specifi ed for input
refl ected ripple current and output noise using designated external input/
output components, circuits and layout as shown in the fi gures below. The
Cbus and Lbus components simulate a typical DC voltage bus. Please note
that the values of Cin, Lbus and Cbus will vary according to the specifi c
converter model.
Minimum Output Loading Requirements
All models regulate within specifi cation and are stable under no load to full
load conditions. Operation under no load might, however, slightly increase
output ripple and noise.
Thermal Shutdown
To prevent many over temperature problems and damage, these converters
include thermal shutdown circuitry. If environmental conditions cause the
temperature of the DC-DCs to rise above the Operating Temperature Range
up to the shutdown temperature, an on-board electronic temperature
sensor will power down the unit. When the temperature decreases below
the turn-on threshold, the converter will automatically restart.
CAUTION: If you operate too close to the thermal limits, the converter
may shut down suddenly without warning. Be sure to thoroughly test your
application to avoid unplanned thermal shutdown.
C IN
V IN
C BUS
L BUS
C IN = 2 x 100µF, ESR < 700mΩ @ 100kHz
C
BUS = 1000µF, ESR < 100mΩ @ 100kHz
L
BUS = 1µH
+VIN
-VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
Figure 4. Measuring Input Ripple Current
Temperature Derating Curves
The graphs in this data sheet illustrate typical operation under a variety of
conditions. The derating curves show the maximum continuous ambient air
temperature and decreasing maximum output current which is accept-
able under increasing forced airfl ow measured in Linear Feet per Minute
(“LFM”). Note that these are AVERAGE measurements. The converter will
accept brief increases in current or reduced airfl ow as long as the average
is not exceeded.
Note that the temperatures are of the ambient airfl ow, not the converter
itself which is obviously running at higher temperature than the outside
air. Also note that very low fl ow rates (below about 25 LFM) are similar to
“natural convection”, that is, not using fan-forced airfl ow. Murata makes
Characterization measurements in a closed cycle wind tunnel with cali-
brated airfl ow. We use both thermocouples and an infrared camera system
to observe thermal performance.
CAUTION: These graphs are all collected at slightly above Sea Level
altitude. Be sure to reduce the derating for higher density altitude.
Output Voltage Sequencing
The OKL modules include a sequencing feature that enables users to
implement various types of output voltage sequencing in their applications.
This is accomplished via an additional sequencing pin. When not using the
sequencing feature, either tie the sequence pin to Vin or leave it uncon-
nected.
When an analog voltage is applied to the sequence pin, the output
voltage tracks this voltage until the output reaches the set-point voltage.
The fi nal value of the sequence voltage must be set higher than the set-
point voltage of the module. The output voltage follows the voltage on the
sequence pin on a one-to-one volt basis. By connecting multiple modules
together, multiple modules can track their output voltages to the voltage
applied on the sequence pin.
For proper voltage sequencing, fi rst, input voltage is applied to the
module. The On/Off pin of the module is left unconnected (or tied to GND
for negative logic modules or tied to Vin for positive logic modules) so that
the module is ON by default. After applying input voltage to the module,
a minimum 10msec delay is required before applying voltage on the
sequence pin. During this time, a voltage of 50mV (± 20 mV) is maintained
on the sequence pin. This delay gives the module enough time to complete
its internal powerup soft-start cycle. During the delay time, the sequence
pin should be held close to ground (nominally 50mV ± 20 mV). This is re-
quired to keep the internal opamp out of saturation thus preventing output
overshoot during the start of the sequencing ramp. By selecting resistor R1
according to the following equation
the voltage at the sequencing pin will be 50mV when the sequencing
signal is at zero. See fi gure 6 for R1 connection for the sequencing signal to
the SEQ pin.
RLOAD
SCOPE
+VOUT
-VOUT
Cext
Figure 5. Measuring Output Ripple and Noise (PARD)
The capacitor Cext value is found on the electrical data page.
R1 = ———— ohms,
Vin – 0.05
23500
OKL2-T/12-W12 Series
Programmable Output 12-Amp iLGA SMT PoL
DC-DC Converter Series
MDC_OKL2-T/12-W12.B02 Page 16 of 19
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