DAC2812D•DAC2815D

APPLICATION

INFORMATION

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.

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.

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:

R =

210 * 10

3

E

(+/– 10% accuracy at 25

O

C)

Set point temperature coefficient is typically + 400ppm/

O

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

4

1

2

150K

10nF

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

NORMAL

TIME

NORMAL

LOAD FAULT

O

Io

O

Rev. B 12/03

6