DAC888_15 Datasheet, PDF(6/12 Page) Analog Devices

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DAC888_15 Datasheet, PDF (6/12 Pages) Analog Devices – 8-BIt LevelTriggered Latch

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IPM!)

DAC-888 BYTEDAC<1I8-BIT HIGH-SPEED "MICROPROCESSOR COMPATIBLE" MULTIPLYING D/A CONVERTER

RECOMMENDED FULL-SCALE ADJUSTMENT CIRCUIT

TABLE 1. REFERENCE AMPLIFIER COMPENSATION

REF. INPUT RESISTANCE

SUGGESTED Cc

MSB

Lsn

DB7 DBn DBS DB4 DB3 DB2 DB1 DBa

1k!l

2.5k!l

5k!l

15pF

37pF

75pF

NOTE: A 001 pF capacitor IS suggested for fixed references.

Rl0

LOW T.C.

CONTROL & LATCHES

For fastest response to a pulse, low values of RlO' enabling

small Cc values, should be used. If pin 10 is driven by a high

current source, none of the above values will suffice and the

'REF' ~ lmA

<S.OOOV -

REF

SOk

POT

4.Sk 10

~ IV 11

VREF'

.14

lOUT'

DAC

VREF-

'OUT I

113

CaMP V- GND V'

amplifier must be heavily compensated which will decrease

overall bandwidth and slew rate. For R 10 = 1k!l and Cc =

15pF, the reference amplifier slews at 4mA//-ls, enabling a

transition from IREF= 0 to IREF= 2mA in 500ns (see Figure,

OBSOLETE APPROX Sk

meter TC effects is shown in the Recommended Full Scale

Adjustment Circuit.

Using lower values of reference current reduces negative

power supply current and increases reference amplifier neg-

ative common mode range. The recommended range for

operation with a DC reference current is +0.2mA to +4.0mA.

The reference amplifier must be compensated by using a

capacitor from pin 12 to V-. For fixed reference operation a

0.01 /-IF capacitor is recommended. For variable reference

applications, see "Reference Amplifier Compensation for

pulsed reference operation I.

Bipolar references may be accommodated by offsetting VREF

or pin 11, as shown in Figure below. The negative common-

mode range of the reference amplifier is given by VCM = V-

plus (IREF X 1k!l) plus 2.5V. The positive common-mode

range is V+ less 1.5V.

When a DC reference is used, a reference bypass capacitor is

recommended. A 5.0V TTL Logic supply is not recom-

mended as a reference. If a regulated power supply is used as

a reference, RlO should be split into two resistors with the

junction bypassed to ground with a 0.1 /-IFcapacitor.

ANALOG OUTPUT CURRENTS

Both true and complemented output sink currents are pro-

vided, where 10 + ro = IFR. Current appears at the "true"

output when a "1" is applied to each logic input. As the binary

count increases, the sink current at pin 14 increases propor-

Multiplying Applications" section.

tionally in the fashion of a "positive logic" D/A converter.

REFERENCE AMPLIFIER COMPENSATION FOR

MULTIPLYING APPLICATIONS

When a "0" is applied to any input bit, that current is turned

off at pin 1~and turned on at pin 13. A decreasing logic count

increases 10 as in a negative or inverted logic 0/ A converter.

AC reference applications will require the reference ampli-

Both outputs may be used simultaneously. If one of the

fier to be compensated using a capacitor from pin 12 to V-.

outputs is not required it must still be connected to ground or

The value of this capacitor depends on the impedance pres-

to a point capable of sourcing IFS; do not leave an unused

ented to pin 10 (see Table 1).

output pin open.

ACCOMMODATING BIPOLAR REFERENCES

MSB

LSB

DB7 DB6 DBS DB4 DB3 DBl DBI DBa

MSB

LSB

DB7 DB6 DBS DB4 DB3 DBl DB, DBa

+VREF

RREF

-IIN

rREF

VIN~

R'N

'HEF .0 NEGATIVE SWING OF IIN

CONTROL & LATCHES

VREF'

VREF-

DAC

lOUT'

'OUT

11 15 9

;p; 16

CONTROL & LA TCHES

-0

'VREF

RREF 10

VREF'

'OUT

VIN

Rl1 11

D-----'VV'v--'-

IOPTIONAL!

DAC

VREF-

CaMP V-

GND

'OUT

HIGH INPUT

IMPEDANCE

nHEF~HI1

l'2 IS

'VHEF MUST BE ABOVE PEAK POSITIVE SWING OF V,N

11-106

7/89, Rev. B

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