DAC8562

REV. A

–12–

Alternatively, the output voltage can be coded in complementary

offset binary using the circuit in Figure 35. This configuration

eliminates the need for a pull-down resistor or an op amp for

REFOUT The transfer equation of the circuit is given by:

V

R2

R1









+ REFOUT

×

R4

R3

+ R4









× 1+

R2

R1









and, for the values shown, becomes:

V

DAC-8562

REFOUT

R1

R4

R3

R2

RANGE

±5V

R2

23.7k + 715

R4

13.7k + 169

R1 = R3 = 10k

Ω

Ω

Figure 35 Bipolar Output Operation Without

Trim Version 2

Generating a Negative Supply Voltage

Some applications may require bipolar output configuration, but

only have a single power supply rail available. This is very com-

mon in data acquisition systems using microprocessor-based sys-

tems. In these systems, only +12 V, +15 V, and/or +5 V are

available. Shown in Figure 36 is a method of generating a nega-

tive supply voltage using one CD4049, a CMOS hex inverter,

operating on +12 V or +15 V. The circuit is essentially a charge

pump where two of the six are used as an oscillator. For the val-

ues shown, the frequency of oscillation is approximately 3.5 kHz

and is fairly insensitive to supply voltage because R1 > 2

R2.

The remaining four inverters are wired in parallel for higher out-

put current. The square-wave output is level translated by C2 to

a negative-going signal, rectified using a pair of 1N4001s, and

then filtered by C3. With the values shown, the charge pump

will provide an output voltage of –5 V for current loading in the

range 0.5 mA

≤ I

OUT

≤ 10 mA with a +15 V supply and

0.5 mA

≤ I

OUT

≤ 7 mA with a +12 V supply.

910

6

11

12

14

15

7

32

5

4

R2

5.1k

R1

510k

C1

0.02µF

C2

47µF

D1

1N4001

C3

47µF

1N5231

5.1V

ZENER

D2

1N4001

R3

470

–5V

INVERTERS = CD4049

Ω

Ω

Ω

Figure 36. Generating a –5 V Supply When

Only +12 V or +15 V Are Available

Audio Volume Control

The DAC8562 is well suited to control digitally the gain or

attenuation of a voltage controlled amplifiers. In professional

audio mixing consoles, music synthesizers, and other audio proces-

sors, VCAs, such as the SSM2018, adjust audio channel gain and

attenuation from front panel potentiometers. The VCA provides a

clean gain transition control of the audio level when the slew rate of

cuit in Figure 37 illustrates a volume control application using the

DAC8562 to control the attenuation of the SSM2018.

15

16

DGND

AGND

DATA

DAC-8562

13

+15V

10

CE

CLR

20

12

0.1µF

4

REF-02

6

2

0.1µF

18k

10pF

470k

P1

100k

Ω

10M

OFFSET

TRIM

47pF

SYMMETRY

TRIM

P2

500k

Ω

+15V

–15V

30k

+15V

–15V

0.1µF

0.1µF

+15V

18k

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

SSM-2018

+5V

1µF

R6

825

R7

1k

0V

* – PRECISION RESISTOR PT146

1k

Ω COMPENSATOR

Ω

Ω

Ω

Ω

Ω

Ω

Figure 37. Audio Volume Control

Since the supply voltage available in these systems is typically

±15 V or ±18 V, a REF02 is used to supply the +5 V required

to power the DAC. No trimming of the reference is required be-

cause of the reference’s tight initial tolerance and low supply

current consumption of the DAC8562. The SSM2018 is config-

ured as a unity-gain buffer when its control voltage equals

Since the SSM2018 exhibits a gain constant of –28 mV/dB

(typical), the DAC’s full-scale output voltage has to be scaled

down by R6 and R7 to provide 80 dB of attenuation when the

sponds to 0.02 dB of attenuation. Table V illustrates the attenu-

ation versus digital code of the volume control circuit.

Table V. SSM2018 VCA Attenuation vs.

DAC8562 Input Code

Hexadecimal Number

Control Voltage

VCA Attenuation

in DAC Register

(V)

(dB)

000

0

0

400

+0.56

20

800

+1.12

40

C00

+1.68

60

FFF

+2.24

80