SPT1018

Figure 4 - CONVert, CONVert Switching Levels

V

IDF

V

ICM MAX

0.0 V

-1.3 V

CONV

CONV

V

ICM MIN

Figure 5A - Standard Load

OUT +

Video Monitor

Inverse

Video

OUT-

RL

75

Ω

75

Ω COAX

RS

75

Ω

RL

75

Ω

75

Ω COAX

RS

75

Ω

SPT1018

Figure 5B - Test Load

Video Out

0 to -1 Volt

OUT +

OUT -

RL

37.5Ω

CL

<5 pF

TYPICAL RGB GRAPHICS SYSTEM

In an RGB graphics system, the color displayed is determined

by the combined intensities of the red, green and blue (RGB)

D/A converter outputs. A change in gain or offset in any of the

RGB outputs will affect the apparent hue displayed on the

CRT screen.

Thus, it is very important that the outputs of the D/A convert-

ers track each other over a wide range of operating condi-

tions. Since the D/A output is proportional to the product of the

reference and digital input code, a common reference should

be used to drive all three D/As in an RGB system to minimize

RGB DAC-to-DAC mismatch and improve TC tracking.

The SPT1019 contains an internal precision bandgap refer-

ence which completely eliminates the need for an external

reference. The reference can supply up to 50

µA to an

external load, such as two other DAC reference inputs. (See

the SPT1019 data sheet).

The circuits shown in figure 6 illustrate how a single SPT1019

may be used as a master reference in a system with multiple

DACs (such as RGB). The other DACs are simply slaved from

the SPT1019’s reference output. The SPT1018s shown are

especially well-suited to be slaved to a SPT1019 for a better

TC tracking from DAC-to-DAC, since they are essentially

SPT1019s without the reference. The SPT1018 is pin-com-

patible with the TDC1018, that does not have an internal

reference. Although either the TDC1018 or the SPT1018 may

be slaved from an SPT1019, the higher performance

SPT1018 and the above mentioned DAC-to-DAC TC track-

ing is the best choice for new designs.

No external reference is required for operation of the

SPT1019, as this function is provided internally. The internal

reference is a bandgap type and is suitable for operation over

extended temperature ranges. The SPT1018 must use an

external reference.

Figure 6 - Typical RGB Graphics System

Ref-

Ref+

750

Ω

500

Ω

750

Ω

500

Ω

R

G

1 k

Ω

Ref-

Ref+

B

1 k

Ω

Ref Out

ISet

R2

750

Ω

R1

500

Ω

IRef

ISet

ISet

ISet

SPT1019

(Master)

SPT1018

(Slave)

SPT1018

(Slave)

Figure 7 - Burn-In Circuit

CONV

1 k

Ω

100

Ω

6.5

Ω

-1.2 V

(Max 1.5 mA)

1 k

Ω

24 Pin DIP

All Resistors Are 5% 1/4 W cc

Clock = -0.9 to -1.7 V, 100 kHz

Ref+

CONV

1 k

Ω

Clock

(Max 60 µA)

-5.9 V

(Max 200 mA)

(Max 50 mA)

Out-

Ref-

Out+

-1.3 V

(Max 60 µA)

1 k

Ω

6.5

Ω

100

Ω

(Max 50 mA)

(Max 1.5 mA)

8

5/14/97