Datasheet

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ULS 30-Watt Series
Sixteenth-brick DOSA-Compatible,
Isolated DC/DC Converters
MDC_ULS-30W_C07 Page 26 of 30
Figure 5. Trim Connections To Increase Output Voltages.
If units have sense pins, Connect trim to + Sense pin.
LOAD
R
TRIM UP
+VOUT
–VIN
+VIN
ON/OFF
CONTROL
TRIM
–VOUT
LOAD
R
TRIM DOWN
+VOUT
–VIN
+VIN
ON/OFF
CONTROL
TRIM
–VOUT
Figure 6. Trim Connections To Decrease Output Voltages.
If units have sense pins, connect Trim to (-) Sense pins.
Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop as the
output current demand increases. If the output voltage drops too low, the mag-
netically coupled voltage used to develop primary side voltages will also drop,
thereby shutting down the PWM controller. Following a time-out period, the
PWM will restart causing the output voltage to begin ramping to their appropri-
ate value. If the short-circuit condition persists, another shutdown cycle will be
initiated. This on/off cycling is referred to as “hiccup” mode. The hiccup cycling
reduces the average output current, thereby preventing internal temperatures
from rising to excessive levels. The ULS Series is capable of enduring an
indefi nite short circuit output condition.
On/Off Control
The input-side, remote On/Off Control function can be ordered to operate with
either logic type:
Positive ("P" suffi x) logic models are enabled when the on/off pin is
left open (or is pulled high, applying +10V to +15V with respect to –Input).
Positive-logic devices are disabled when the on/off pin is pulled low (0 to 0.7V
with respect to –Input).
Negative (“N” suffi x) logic devices are off when pin is left open (or pulled
high, applying +2.5V to +15V), and on when pin is pulled low (-0.1 to 0.8V)
with respect to –Input as shown in Figure 4.
Dynamic control of the remote on/off function is best accomplished with a
mechanical relay or an open-collector/open-drain drive circuit (optically isolated
if appropriate). The drive circuit should be able to sink appropriate current (see
Performance Specifi cations) when activated and withstand appropriate voltage
when deactivated. Applying an external voltage to pin 2 when no input power is
applied to the converter can cause permanent damage to the converter.
Thermal Shutdown
The ULS converters are equipped with thermal-shutdown circuitry. If environ-
mental conditions cause the temperature of the DC/DC converter to rise above
the designed operating temperature, a precision temperature sensor will power
down the unit. When the internal temperature decreases below the threshold
of the temperature sensor, the unit will self start. See Performance/Functional
Specifi cations.
Output Over-Voltage Protection
The ULS output voltage is monitored for an over-voltage condition using a com-
parator. The signal is optically coupled to the primary side and if the output volt-
age rises to a level which could be damaging to the load, the sensing circuitry
will power down the PWM controller causing the output voltage to decrease.
Following a time-out period the PWM will restart, causing the output voltage
to ramp to its appropriate value. If the fault condition persists, and the output
voltage again climbs to excessive levels, the over-voltage circuitry will initiate
another shutdown cycle. This on/off cycling is referred to as “hiccup” mode.
Current Limiting
As soon as the output current increases to approximately 130% of its rated
value, the DC/DC converter will go into a current-limiting mode. In this condi-
tion, the output voltage will decrease proportionately with increases in output
current, thereby maintaining somewhat constant power dissipation. This is
commonly referred to as power limiting. Current limit inception is defi ned
as the point at which the full-power output voltage falls below the specifi ed
tolerance. See Performance/Functional Specifi cations. If the load current, being
drawn from the converter, is signifi cant enough, the unit will go into a short
circuit condition as described below.
C1
C1 = 1μF
C2 = 10μF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
–VOUT
Figure 3. Measuring Output Ripple/Noise (PARD)
+Vcc
13V CIRCUIT
5V CIRCUIT
–VIN
O N /O F F
C O N TR O L
+VIN
Figure 4. Driving the Negative Logic On/Off Control Pin (simplifi ed circuit)