ADDC02812DA/ADDC02815DA
BASIC O P ERATIO N
P IN CO NNECTIO NS
T he ADDC02812DA and ADDC02815DA converters use a
flyback topology with dual interleaved power trains operating
180° out of phase. Each power train switches at a fixed fre-
quency of 500 kHz, resulting in a 1 MHz fixed switching fre-
quency 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.
P ins 1 and 2 (؎SENSE)
Pins 1 and 2 must always be connected for proper operation,
although failure to make these connections will not be cata-
strophic to the converter under normal operating conditions. If
there is no load present on the converter, failure to make these
connections could result in damage to the device. Pin 1 must
always be connected to the output return and Pin 2 must always
be connected to +VOUT when regulating the positive voltage. If
the negative output voltage is being regulated, Pin 1 must always
be connected to –VOUT and Pin 2 must always be connected to
the output return. T hese connections can be made at any one
of the output pins of the converter, or remotely at the load. A
remote connection at the load can adjust for voltage drops of as
much as 0.25 V dc between the converter and the load. Long
remote sense leads can affect converter stability, although this
condition is rare. The impedance of the long power leads between
the converter and the remote sense point could affect the
converter’s unity gain crossover frequency and phase margin.
Consult factory if long remote sense leads are to be used.
A five-pole differential input EMI filter, along with a common-
mode EMI capacitor and careful attention to layout parasitics,
is designed to meet all applicable requirements in MIL-ST D-
461D when installed in a typical system setup. A more detailed
discussion of CE102 and other EMI issues is included in the
section entitled EMI Considerations.
T he converters use current mode control and employ a high
performance opto-isolator in their feedback path to maintain
isolation between input and output. T he control circuits are
designed to give a nearly constant output current as the output
voltage drops from VO nom to VSC during a short circuit condi-
tion. It does not let the current fold back below the maximum
rated output current. T he output overvoltage protection cir-
cuitry, 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.
P in 3 (AD JUST)
An adjustment pin is provided so that the user can change the
nominal output voltage during the prototype stage. Since very
low temperature coefficient resistors are used to set the output
voltage and maintain tight regulation over temperature, using
standard external resistors to adjust the output voltage will
loosen output regulation over temperature. Furthermore, since
the status trip point is not changed when the output voltage is
adjusted using external resistors, the status line will no longer
trip at the standard levels of the newly adjusted output voltage.
T herefore, it is highly recommended that once the correct out-
put voltage is determined, modified standard units should be
ordered with the necessary changes made inside the package at
the factory. T he ADJUST function is sensitive to noise, and
care should be taken in the routing of connections.
An input overvoltage protection feature shuts down the con-
verter when the input voltage exceeds (nominally) 52.0 V dc.
An internal temperature sensor shuts down the unit and pre-
vents it from becoming too hot if the heat removal system fails.
T he temperature sensed is the case temperature and is factory
set to trip at a nominal case temperature of 110°C to 115°C.
T he shutdown temperature setting can be raised externally or
disabled by the user.
To make the output voltage higher, place a resistor from ADJUST
(Pin 3) to –SENSE (Pin 1). T o make the output voltage lower,
place a resistor from ADJUST (Pin 3) to +SENSE (Pin 2).
Figures 18 and 19 show resistor values for a ±5% change in
output voltage.
Each unit has an INHIBIT pin that can be used to turn off the
converter. T his feature can be used to sequence the turn-on of
multiple converters and to reduce input power draw during
extended time in a no load condition.
8
7
6
5
4
3
2
1
A SYNC pin, referenced to the input return line (Pin 10), is
available to synchronize multiple units to one switching fre-
quency. T his feature is particularly useful in eliminating beat
frequencies which may cause increased output ripple on paral-
leled 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.
99
98
97
96
95
OUTPUT VOLTAGE – %
Figure 18. External Resistor Value for Reducing Output
Voltage
REV. A
–8–
ADI [ ADI ]
