MYLG100503 Series
Programmable Output 3-Amp LGA-SMT PoLs
APPLICATION NOTES
Specification Notes, Cont.:
(7) Please observe the voltage input and output specifications in the Voltage Range Graph on page 7.
Input Fusing
(8) Output noise may be further reduced by adding an external filter. At zero output current, the output may
contain low frequency components which exceed the ripple specification. The output may be operated
indefinitely with no load.
Certain applications and/or safety agencies may require fuses at the inputs
of power conversion components. Fuses should also be used when there
is the possibility of sustained input voltage reversal which is not current-
limited. We recommend a time delay fuse installed in the ungrounded input
supply line with a value which is approximately twice the maximum line
current, calculated at the lowest input voltage.
(9) All models are fully operational and meet published specifications, including “cold start” at –40ꢀ C.
(10) Regulation specifications describe the deviation as the line input voltage or output load current is varied
from a nominal midpoint value to either extreme.
(11) Other input or output voltage ranges will be reviewed under scheduled quantity special order.
(12) Maximum PC board temperature is measured with the sensor in the center of the converter.
(13) Do not exceed maximum power specifications when adjusting the output trim.
(14) The maximum output capacitive loads depend on the the Equivalent Series Resistance (ESR) of the external
output capacitor and, to a lesser extent, the distance and series impedance to the load. Larger caps will
reduce output noise but may change the transient response. Newer ceramic caps with very low ESR may
require lower capacitor values to avoid instability. Thoroughly test your capacitors in the application. Please
refer to the Output Capacitive Load Application Note.
The installer must observe all relevant safety standards and regulations.
For safety agency approvals, install the converter in compliance with the
end-user safety standard, i.e. IEC/EN/UL 60950-1.
(15) Do not allow the input voltage to degrade lower than the input undervoltage shutdown voltage at all times.
Otherwise, you risk having the converter turn off. The undervoltage shutdown is not latching and will
attempt to recover when the input is brought back into normal operating range.
Input Under-Voltage Shutdown and Start-Up Threshold
Under normal start-up conditions, converters will not begin to regulate
properly until the ramping-up input voltage exceeds and remains at the
Start-Up Threshold Voltage (see Specifications). Once operating, convert-
ers will not turn off until the input voltage drops below the Under-Voltage
Shutdown Limit. Subsequent restart will not occur until the input voltage
rises again above the Start-Up Threshold. This built-in hysteresis prevents
any unstable on/off operation at a single input voltage.
(16) The outputs are not intended to sink appreciable reverse current.
(17) “Hiccup” overcurrent operation repeatedly attempts to restart the converter with a brief, full-current output.
If the overcurrent condition still exists, the restart current will be removed and then tried again. This short
current pulse prevents overheating and damaging the converter. Once the fault is removed, the converter
immediately recovers normal operation.
Output Voltage Adustment
The output voltage may be adjusted over a limited range by connecting an
external trim resistor (Rtrim) between the Trim pin and Ground. The Rtrim
resistor must be a 1/10 Watt precision metal film type, 0.5% accuracy or
better with low temperature coefficient, 100 ppm/oC. or better. Mount the
resistor close to the converter with very short leads or use a surface mount
trim resistor.
Users should be aware however of input sources near the Under-Voltage
Shutdown whose voltage decays as input current is consumed (such as
capacitor inputs), the converter shuts off and then restarts as the external
capacitor recharges. Such situations could oscillate. To prevent this, make
sure the operating input voltage is well above the UV Shutdown voltage AT
ALL TIMES.
In the tables below, the calculated resistance is given. Do not exceed the
specified limits of the output voltage or the converter’s maximum power
rating when applying these resistors. Also, avoid high noise at the Trim
input. However, to prevent instability, you should never connect any capaci-
tors to Trim.
Start-Up Time
Assuming that the output current is set at the rated maximum, the Vin to
Vout Start-Up Time (see Specifications) is the time interval between the
point when the ramping input voltage crosses the Start-Up Threshold and
the fully loaded regulated output voltage enters and remains within its
specified accuracy band. Actual measured times will vary with input source
impedance, external input capacitance, input voltage slew rate and final
value of the input voltage as it appears at the converter.
MYLG1
Output Voltage
5.0 V.
Calculated Rtrim (KΩ)
1.34
3.3 V.
2.18
These converters include a soft start circuit to moderate the duty cycle of
its PWM controller at power up, thereby limiting the input inrush current.
2.5 V.
3.1
2.0 V.
4.19
The On/Off Remote Control interval from On command to Vout regulated
assumes that the converter already has its input voltage stabilized above
the Start-Up Threshold before the On command. The interval is measured
from the On command until the output enters and remains within its
specified accuracy band. The specification assumes that the output is fully
loaded at maximum rated current. Similar conditions apply to the On to Vout
regulated specification such as external load capacitance and soft start
circuitry.
1.8 V.
4.88
1.5 V.
6.50
1.2 V.
9.70
1.0 V.
14.45
∞ (open)
0.591 V.
Resistor Trim Equation, MYLG1 models:
5.91
VOUT – 0.591
_____________
Input Source Impedance
RTRIM (kꢀ) =
These converters will operate to specifications without external compo-
nents, assuming that the source voltage has very low impedance and
reasonable input voltage regulation. Since real-world voltage sources
have finite impedance, performance is improved by adding external filter
components. Sometimes only a small ceramic capacitor is sufficient. Since
it is difficult to totally characterize all applications, some experimentation
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