DAC2812D • DAC2815D
OUTPUT ADJUST / COMP
The output voltage of the DAC2800D may be adjusted from
90% to 110% of nominal value by the use of a 150K( potenti-
ometer as shown. Adjustment beyond this range is possible,
however certain characteristics of the converter such as but
not limited to input voltage range, efficiency, ripple and tem-
perature performance will change. Characterization by the
user is recommended in such applications.
APPLICATION
INFORMATION
low for at least 100 mS and return high. If the load fault is still
present pin 5 will return low and the cycle will repeat. A resistor
> 400K( from pin 5 to 7 provides pull down for pin 5 if there is
no input setpoint programming resistor already in place.
LOAD FAULT RESPONSE
The DAC2800D series of DC-DC converters share load
fault philosophies. Load fault conditions include short-circuit
and severe overload conditions. The DAC2800D converter
series responds to load faults by turning off all power conver-
sion circuits for 250 mS and then attempting to restart for 10
mS (typical). The net "on" duty factor during a fault is very low
resulting in low converter dissipation and immunity from
overheating at 125°C. Current beyond rated can flow into the
load at startup time. This allows the converter to bring up
capacitive and other difficult load types more reliably than
competing converters.
Vo
O
4
1
2
150K
10nF
Adjust/comp (pin 4) may be driven by external circuitry
referenced to pin 2 (-output) if desired. Grounding pin 4 causes
voltage to increase (25% typically) while driving pin 4 above
1.3 V causes output voltage to decrease. Pin 4 may be driven
negative without damage, however the resultant increase in
converter output voltage should be considered. Pin 4 may be
driven through 10K( or more if connection of the comp function
is also required.
The comp function of pin 4 allows load transient response
to be tailored to suit specific application requirements. This
feature may be utilized by connecting a 10nF or less capacitor
between pins 4 and 1.
I
o
O
SHUTDOWN PLUS
Pin 5 is used for remote shutdown, output fault detection,
and/or setting the input voltage point at which the converter
will turn on as shown in the typical application diagram. No
connection to pin 5 is necessary for normal operation of the
converter. Pin 5 is referenced to pin 7 (-input).
Shutdown may be implemented by simply connecting pin 5
to an open collector logic output or switch rated at 2.5 mA, 25
Vdc or higher.
Input voltage turn on point is programmed with a single
resistor from pin 5 to 7. An input turn on/off hysteresis (typically
3.5% of Vin) will be observed. This should be considered when
making or verifying set point adjustment. The value of the
setpoint resistor may be determined by the following:
NORMAL
TIME
LOAD FAULT
NORMAL
210 * 10
3
R =
E
TO
– 9.5
(+/– 10% accuracy at 25 C)
O
O
Set point temperature coefficient is typically + 400ppm/ C
Output fault monitoring is accomplished by observing pin 5
with a high impedance monitoring circuit. Pin 5 voltage drops
from over 10 V to below 1 V when a load fault causes the
converter's fault protection circuitry to activate. It will remain
6
Rev. B 12/03
MSK [ M.S. KENNEDY CORPORATION ]
