ADDC02808PB(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADDC02808PB Datasheet PDF : 20 Pages
| |||
ADDC02808PB
BASIC OPERATION
multiple converters and to reduce input power draw during
The ADDC02808PB converter uses a flyback topology with
extended time in a no load condition.
dual interleaved power trains operating 180° out of phase. Each
power train switches at a fixed frequency of 500 kHz, resulting
in a 1 MHz fixed switching frequency as seen at the input and
output of the converter. In a flyback topology, energy is stored
in the inductor during one half portion of the switching cycle
and is then transferred to the output filter during the next half
portion. With two interleaved power trains, energy is transferred
to the output filter during both halves of the switching cycle,
resulting in smaller filters to meet the required ripple.
A five pole differential input EMI filter, along with a common-
A SYNC pin, referenced to the input return line (Pin 10), is
available to synchronize multiple units to one switching
frequency. This feature is particularly useful in eliminating
beat frequencies which may cause increased output ripple on
paralleled units. A current share pin (ISHARE) is available which
permits paralleled units to share current typically within 5% at
full load.
A low level dc auxiliary voltage supply referenced to the input
return line is provided for miscellaneous system use.
mode EMI capacitor and careful attention to layout parasitics, is PULSED OUTPUT POWER VS. PULSE LENGTH
OBSOLETE designed to meet all applicable requirements in MIL-STD-461D
when installed in a typical system setup. Due to the higher output
level in this product compared to the 100 W continuous output
products, input stability is more of a concern. As a result, the two
inductors in the internal input EMI filter have smaller values of
inductance to mitigate input stability concerns. The effectiveness of
the internal input EMI filter is, therefore, slightly diminished
compared to these other products. A more detailed discussion
of CE102 and other EMI issues is included in the section
entitled “EMI Considerations.”
The maximum available peak power out is 200 W and is based
on a combination of maximum junction temperatures, maximum
pulse width, and maximum duty cycle. Refer to section entitled,
“Pulsed Output Power vs. Pulse Length,” for peak power
derating curves for varying conditions.
The unit is compensated for ultrafast transient response with
minimum output voltage deviation. The compensation has been
The maximum specified pulsed output power in the standard
configuration of the ADDC02808PB is 200 W. This limit is
based on issues of working down to the minimum input
voltage, of providing a reasonable short circuit current limit,
and so on. However, this power level assumes that the
junction temperatures of the converter’s power semiconductor
devices have not exceeded 110°C. For short pulse lengths and
low duty cycles, this condition will be met. Otherwise, the
pulsed output power will have to be reduced to keep the
junction temperatures below 110°C if NAVMAT guidelines are
to be followed.
Figures 16 and 17 show the tradeoff that must be made
between the highest allowable pulsed output power and the
pulse length. Notice that for each curve, as the pulse length is
made longer, the pulsed power that causes a 110°C junction
temperature to be reached is lower. The curves are provided
for two baseplate temperatures (25°C and 90°C) and three
optimized and output stability insured for an external load
average output powers. The duty cycle that corresponds to any
capacitance in the range of 500 µF, 20 mΩ ESR to 4,000 µF,
point on a curve can be calculated by dividing the average
2.5 mΩ ESR. Peak performance and output stability are depen-
power by the pulsed power for that point. The curves
dent on minimizing parasitic inductance and resistance in the con- represent typical upper limits; operation anywhere below the
nection from the converter to the load.
curves is acceptable and will result in cooler junctions.
The converter uses current mode control and employs a high
performance opto-isolator in its feedback path to maintain
isolation between input and output. The control circuit is
designed to give a nearly constant output current as the output
voltage drops from VO nom to VSC during a short circuit
condition. It does not let the current fold back below the
maximum rated output current. The output overvoltage
protection circuitry, which is independent from the normal
feedback loop, protects the load against a break in the remote
sense leads. Remote sense connections, which can be made at
the load, can adjust for voltage drops of as much as 0.25 V dc
between the converter and the load, thereby maintaining an
accurate voltage level at the load.
An input overvoltage protection feature shuts down the con-
verter when the input voltage exceeds (nominally) 52.5 V dc.
The ADDC02808PB is designed to deliver a continuous 100
watts to its output while keeping its hottest junction tempera-
ture below 110°C with a baseplate temperature of 90°C.
250
MAXIMUM PEAK
POWER LIMIT
200
10W ave
100W ave
150
50W ave
100
MAXIMUM CONTINUOUS
POWER LIMIT
50
An internal temperature sensor shuts down the unit and
prevents it from becoming too hot if the heat removal system
fails. The temperature sensed is the case temperature and is
factory set to trip at a nominal case temperature of 110°C to
115°C. The shut down temperature setting can be raised
externally or disabled by the user.
Each unit has an INHIBIT pin that can be used to turn off the
converter. This feature can be used to sequence the turn-on of
0
0
100
200
300
400
500
600 700
PULSE WIDTH – ms
Figure 16. Largest On-State Power vs. Pulse Width that
Maintains TJMAX ≤ 110°C at 25°C Baseplate
REV. 0
–7–
Share Link: 