Absolute Maximum Ratings
Input Voltage:
Continuous: D12 Models 21 Volts
D24 Models 40 Volts
D48 Models 81 Volts
Transient (100msec): D12 Models 25 Volts
D24 Models 50 Volts
D48 Models 100 Volts
Input Reverse-Polarity Protection:
➁ Input Current must be limited. 1 minute
duration. Fusing recommended.
D12 Models 3 Amps
D24 Models 2 Amps
D48 Models 1 Amps
Output Current
➁ Current limited. Devices can withstand
an indefi nite output short circuit.
On/Off Control (Pin 3) Max. Voltages:
Referenced to –Input (pin 2) +15V
Storage Temperature –40 to +120°C
Lead Temperature (Soldering, 10 sec.) +300°C
These are stress ratings. Exposure of devices to greater than any of these conditions may
adversely affect long-term reliability. Proper operation under conditions other than those
listed in the Performance/Functional Specifi cations Table is not implied, nor recommended.
TECHNICAL NOTES
Isolation / Case Connection
The XWR Series’ 5V and 3.3V outputs (pins 5 & 8) with its common return (pin
7) are isolated from the +V
IN and –VIN inputs (pins 1 & 2) via a transformer
and an opto-coupled transistor.
The DC/DC converter’s case is internally connected to pin 4. This allows
circuit specifi c grounding of the case on either the input or the output side, or
leaving the case disconnected, i.e. “fl oating.”
Input Fusing
Certain applications and/or safety agencies may require the installation of
fuses a
t the inputs of po
wer conversion components. Fuses should also be
used if the possibility of a sustained, non-current-limited, input-voltage polar-
ity reversal exists. For XWR 15 Watt Series Converters, it is recommended to
install slow blow fuses with values no greater than the following, in the +Input
line.
V
IN Range Fuse Value
D12 Models 3 Amps
D24 Models 2 Amps
D48 Models 1 Amps
Input Reverse-Polarity Protection
Upon applying a reverse-polarity voltage to the DC/DC converter, an internal
diode will be forward biased,
dra
wing excessive current from the power
source. Therefore, it is required that the input current be limited by either an
appropriately rated input fuse or a current limited power source.
Input Overvoltage/Undervoltage Shutdown and Start-Up Threshold
Under normal start-up conditions, devices will not begin to regulate until the
ramping-up input volta
ge exceeds the Start-Up
Threshold Voltage (35V for
D48 models). Once operating, devices will not turn off until the input voltage
drops below the Undervoltage Shutdown limit (34V for D48 models). Subse-
quent re-start will not occur until the input is brought back up to the Start-Up
Threshold. This built in hysteresis prevents any unstable on/off situations from
occurring at a single input voltage.
Input voltages exceeding the input overvoltage shutdown specifi cation listed
in the Performance/Functional Specifi cations will cause the device to shut-
down. A built-in hysteresis of 0.6 to 1.6 Volts for all models will not allow the
converter to restart until the input voltage is suffi ciently reduced.
Start-Up Time
The V
IN 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 specifi ed accuracy band. Actual measured times will
vary with input source impedance, external input/output capacitance, and
the slew rate of the input voltages. The XWR 15 Watt 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 V
OUT start-up time assumes the converter has its
nominal input voltage applied but is turned off via the On/Off Control pin. The
specifi cation defi nes the interval between the time at which the converter is
turned on and the fully loaded output voltage enters and remains within its
specifi ed accuracy band. Similar to the V
IN to VOUT start-up, the On/Off Control
to V
OUT start-up time is also governed by the internal soft start circuitry and
external load capacitance.
On/Off Control
The On/Off Control (pin 3) may be used for remote on/off operation. As shown
in F
igure 1,
the control pin is referenced to the –Input (pin 2) and will be inter-
nally pulled to a high state. The XWR Series is designed so that it is enabled
when the control pin is left open (pulled high) and disabled when the control
pin is pulled low (less than +0.8V relative to –Input).
Dynamic control of the on/off function is best accomplished with a mechani-
cal relay or an open-collector/open-drain circuit (optically isolated if appropri-
ate). The drive circuit should be able to sink approximately 1 mA for logic low.
The on/off control function is designed such that the converter can be
disabled while the input power is ramping up, and then “released” once the
input has stabilized.
3
2
13V CIRCUIT
+Vcc
5V CIRCUIT
–INPUT
ON/OFF
CONTROL
Figure 2. Internal On/Off Control circuitry
DSM/DWR Models
Dual Output, 3.3V and 5V, 15Watt DC/DC Converters
MDC_DSM/DWR Models.D03 Page 4 of 9
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