MAX5140 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX5140

8-Bit, Ultra-High-Speed DAC

Maxim Integrated 

8-Bit, Ultra-High-Speed DAC

This device also has two analog ground pins (VCC). Tie

both ground pins to the analog ground plane. All power

and ground pins must be connected in any application.

If a +5V power source is required, the VCC ground

pins become the positive supply pins, while the VEE

supply pins become the ground pins. The relative

polarities of the other input and output voltages must

be maintained.

Reference Considerations

The MAX5140 has two reference inputs (Ref In and ISet)

and one reference output (Ref Out). The input pins are

connected to the inverting and noninverting inputs of

an internal amplifier that serves as a reference buffer.

The buffer amplifier’s output is the reference for the cur-

rent sinks. The amplifier feedback loop is connected

around one of the current sinks to achieve better accu-

racy. (See Figure 3.)

Since the analog output currents are proportional to the

digital input data and ISet, full-scale output can be

adjusted by varying the reference current. ISet is con-

trolled through the MAX5140’s ISet input. Figure 1

shows the method and the necessary equations for set-

ting ISet. The MAX5140 can use an external negative-

voltage reference. The external reference must be sta-

ble to achieve a satisfactory output, and Ref In should

be driven through a resistor to minimize offsets caused

by bias current. To change the full-scale output,

vary the value for ISet with the 500Ω to 1kΩ trimmer.

A double 50Ω load (25Ω) can be driven if ISet is

increased by 50% for doubly terminated 75Ω video

applications.

Data Inputs and Video Controls

The MAX5140 has standard, single-ended data inputs.

The inputs are registered to produce the lowest differ-

ential data-propagation delay (skew) to minimize glitch-

ing. Also, four video-control inputs generate composite

video outputs: sync, blank, bright, and reference white

(force high). Feedthrough control is also provided. All

of the controls and data inputs are ECL compatible. In

addition, all have internal pulldown resistors to leave

them at a logic low so the pins are inactive when not

used. This is useful if the devices are applied as stan-

dard DACs without the need for video controls, or if

fewer than eight bits are used.

The MAX5140 is usually configured in synchronous

mode. In this mode, the controls and data are synchro-

nized to prevent pixel dropout. This reduces screen-

edge distortions and provides the lowest output noise

while maintaining the highest conversion rate. With the

FT control open (low), each rising edge of the convert

clock (CONV) latches decoded data and control values

into a D-type internal register. The switched-current

sinks convert the registered data into the appropriate

analog output. When FT is tied high, the control inputs

and data are not registered. The analog output asyn-

chronously tracks the input data and video controls.

Feedthrough itself is asynchronous and is usually used

as a DC control.

Figure 3. Reference Buffer and DAC Output Circuit

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