Datasheet

On/Off Control
The input-side, remote On/Off Control function (pin 3) can be ordered to operate
with either polarity. Positive-polarity devices ("C" suffix) are enabled when pin
3 is left open (or is pulled high, +13V to VIN applied with respect to –Input, pin
2, see Figure 2). Positive-polarity devices are disabled when pin 3 is pulled low
(0-0.8V with respect to –Input). Negative-polarity devices are off when pin 3 is
left open (or pulled high, 3.5V to VIN), and on when pin 3 is pulled low (0-0.5V).
See Figure 5.
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 Specs) when activated and withstand appropriate voltage when
deactivated.
Applying an external voltage to pin 3 when no input power is applied to the
converter can cause permanent damage to the converter.
3
2
1
+INPUT
13V CIRCUIT
5V CIRCUIT
–INPUT
ON/OFF
CONTROL
Figure 4. Driving the Positive Polarity On/Off Control Pin
Figure 5. Driving the Negative Polarity On/Off Control Pin
Start-Up Time
The VIN to VOUT start-up time is the interval of time where the input voltage crosses
the turn-on threshold point, and the fully loaded output voltage enters and remains
within its specified accuracy band. Actual measured times will vary with external
output capacitance and load. The BWR 15-17W Series implements a soft start
circuit that limits the duty cycle of the PWM controller at power up, thereby limiting
the Input Inrush current.
The On/Off Control to VOUT start-up time assumes the converter has its nominal
input voltage applied but is turned off via the On/Off Control pin. 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.
Similar to the VIN to VOUT start-up, the On/Off Control to VOUT start-up time is also
governed by the internal soft start circuitry and external load capacitance.
If loading from +/– Outputs to Output Return is symmetrical, the voltage at
Output pins with respect to Output Return will also be symmetrical. An unbal-
ance in loading will consequently result in a degraded VOUT regulation accuracy
from +/– Outputs to Output Return ( –Output to +Output regulation will still be
within specification) with a load step from minimum to maximum load and with
the other output at full load, the maximum deviation is 2.5% VOUT nominal.
3
2
1
+INPUT
–INPUT
ON/OFF
CONTROL
15.5
15.4
15.3
15.2
15.1
15
14.9
14.8
14.7
BWR-15/575-D48A Unbalanced Output Load Regulation
Output Load Regulation (%)
+/–15VOUT
 0 10 20 30 40 50 60 70 80 90 100
+15V @ 0A to 0.575A
–15V @ 0.575A
–15V @ 0A to 0.575A
+15V @ 0.575A
Current Limiting
When output current increases to approximately 15% to 50% above the rated
output current, the DC/DC converter will go into a current limiting mode. In
this condition the output voltage will decrease proportionately with increases
in output current, thereby maintaining a somewhat constant power dissipa-
tion. This is commonly referred to as power limiting. Current limit inception
is defined as the point where the full-power output voltage falls below the
specified tolerance. See Performance/Functional Specifications. If the load
current being drawn from the converter is significant enough, the unit will go
into a short circuit condition. See "Short Circuit Condition."
Short Circuit Condition
When a converter is in current limit mode the output voltages will drop as
the output current demand increases. If the output voltage drops too low, the
magnetically 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 voltages
to begin ramping to their appropriate values. 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 BWR 15-17W Series is capable of enduring an indefinite short
circuit output condition.
Thermal Shutdown
These BWR converters are equipped with Thermal Shutdown Circuitry. If
environmental conditions cause the internal temperature of the DC/DC con-
verter rises above the designed operating temperature, a precision tempera-
ture sensor will power down the unit. When the internal temperature decreases
below the threshold of the temperature sensor the unit will self start.
Figure 4. Output Voltage Accuracy vs. Imbalanced Loading
BWR Series
15-17W, Dual Output DC/DC Converters
MDC_BWR15-17W.D01 Page 5 of 9
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