SP9841 datasheet(24/32 Pages) SIPEX

24 / 32 page

290

Figure9showsaDACchannelcontrollingtheoutput

voltage of an LM317 voltage regulator. By program-

ming the code, the DAC changes its own supply

voltage. This circuit can be modified for wider output

voltage ranges by reducing the value of R

4. However,

the circuit as shown requires the DAC to sink 1mA to

the negative rail at code 0 at its lowest V

DD, at which

pointtheoutputvoltageis62mV.Thus,programming

codes 0 through 5 will do little to influence the output.

If R

4 is replaced with a short circuit, useful operation

would be between 3.9V and 6.15V output; however,

the DAC output must then sink 2.5mA at V

DD = 3.9V,

which results in a minimum DAC output voltage of

Figure 9. Programmable 1Amp Power Source.

–

OUT

1/8 of SP9841

+12V

ICL8069

At PRESET, V

OUT = 5.0V

10kOhms

499Ohms

OUT = 4.5V TO 5.5V at 1Amp for DATA = 00H to FFH.

LM317

10µF

Out

Adjust

1kOhms

511Ohms

1.22V

VDD

681Ohms

around 150mV. Codes above 17 will then provide

equally spaced output voltage increments.

Figure 10 shows how the gain of an external non–

inverting op amp can be programmed. R

F and RG are

chosen for nominal gain. R

TRIMRANGE is then ratioed to

F to provide the desired range of gain trim. A wide

gain grange is achievable — for example, with R

F =

11kOhms,R

G=1kOhmsandRTRIMRANGE=2.74kOhms,

gain would be programmed linearly from 8 to just

under 16.

The OP–491 shown in Figure 10 is capable for

Figure 10. Adjustable Gain of External Non–Inverting Opamp Circuit; V

OUT = Rail–to–rail.

–

SIG OUT

1/8 of SP9841

1/4 of OP–491

+5V

Set R

TRIMRANGE for desired gain-trim range.

For R

TRIMRANGE = 20kOhms:

Code 0, A

V = +5.5

Code 128, A

V = +5.0

Code 255, A

V = +4.51

–

10kOhms

RTRIMRANGE

20kOhms

RIBIAS

50kOhms

REFL

= Up to VDD/2

(2.5V nominal for

rail–to–rail output

at SIG OUT)

P-P

2.2µF

RGAIN

2.5kOhms

REFL

TRIMRANGE

+ −









128

, D = 0 to 255

+5V

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