SPT5140 datasheet(5/12 Pages) CADEKA

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SPT5140

OUTPUT CONSIDERATIONS

The analog outputs are designed to directly drive a dou-

bly terminated 50 or 75 ohm load transmission system as

shown. The source impedances of the SPT5140 outputs

are high impedance current sinks. The load impedance

(RL) must be 25 or 37.5 ohms to attain standard RS-343-

A video levels. Any deviation from this impedance will

affect the resulting video output levels proportionally. As

with the data interface, it is important that the analog

transmission lines have matched impedance throughout,

including connectors and transitions between printed

wiring and coaxial cable. The combination of matched

source termination resistor RS and load terminator RL

minimizes reflections of both forward and reverse travel-

ing waves in the analog transmission system. The return

path for analog output current is VCC, which is connected

to the source termination resistor RS.

POWER CONSIDERATIONS

The SPT5140 operates from a single –5.2 V standard

supply. Proper bypassing of the supplies will augment the

SPT5140’s inherent supply noise rejection characteris-

tics. As shown in figure 2, each supply pin should be by-

passed as close to the device as possible with 0.01

µF

and 10

µF capacitors.

The SPT5140 has two analog (VEE) power supply pins.

Both supply pins should be properly bypassed as men-

tioned previously. This device also has two analog (VCC)

ground pins. Both ground pins should be tied to the

analog ground plane. Power and ground pins must be

connected in all applications. If a +5 V power source is

required, the ground pins (VCC) become the positive sup-

ply pins while the supply pins (VEE) become the ground

pins. The relative polarities of the other input and output

voltages must be maintained.

Figure 2 – Typical Interface Circuit

10.

= VCC = AGND

See figure 9 for detail on Ref Buffer.

1 k

Ω

4 to 15

Decode

Video

Control

Inputs

Video

Data

Inputs

Clock

)

(

Ref

Buffer

V+

1 k

Ω

ISet

Bandgap

Reference

V–

Ref In

Ω

Optional External

Reference

–5.2 V

.01

µF

Remove J1 For

External Reference

LM113/313

Blank

BRT

Sync

D0 (LSB)

D7 (MSB)

CONV

2 k

Ω

Video Monitor

Out+

50/75

Ω

50/75

Ω

50/75

Ω COAX

All reference resistors 1/8 W 1% metal

film, power supply decoupling 50 V

ceramic disc

NOTES:

V– = –1.2 V (typical) for LM113 or VBG

V+ = –1.2 V

RL = R3 / / R4

K = 15.8069

K1 = 1.7617

K2 = 10.0392

FB = Ferrite bead, Fair-rite pin 217430011

or equivalent.

= ECL Termination

ISet =

V+

αT(R

1+R2)

; typ = 1.105 mA

VOUT =

255

VSync = (K x ISet x RL) + (K2 x ISet x RL)

*An external reference can be used or the reference from

Ref Out can drive three SPT5140s.

Out–

255–Digital Input Code

xISet RL +

1 x ISet x RL(bright)

VEE

VCC

–5.2 V

.01

µF

= DGND (digital input drivers).

12.

[

]

11.

3/28/00

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