REF5050 datasheet(14/43 Pages) TI1

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4-Bit

Counter

Reset

SYNC

CLK

CLK/16

Reset

Digital

Modulator

SW/TD

Reset

Current

Generator

Current Taps

Tap

Control

Common-Mode

Current

Amplifier

Summing

Nodes

AVDD

VREF

AVSS

Sine Wave

Table

Digital

Data

Mux

...

DAC1282

SBAS490

– DECEMBER 2011

www.ti.com

The SYNC input synchronizes the output signal to a known time reference. In sine mode, SYNC resets the sine

wave to the zero crossing. In Pulse mode, SYNC selects one of two user-programmed dc levels.

The RESET/PWDN pin powers down the device when low. When RESET/PWDN is released high, the DAC1282

is reset.

The SW/TD input is dual function. In digital data mode, the pin is the ones-density data input. In the other modes,

SW/TD controls the opening/closing of the switch.

Figure 33 shows the main details of the main DAC. The main DAC provides the digital-to-analog conversion by

filtering the ones-density digital data. In operation, the current generator establishes the range current that is

mirrored to a multi-tap, current-steering filter stage. The current generator is controlled by the analog gain control

–36 dB).

The current-steering stage switches the tap currents to the positive or negative current summing nodes, as the

digital input is sampled. A higher ones-density directs an increasing average current to one node than the other,

thus increasing the differential current. The differential current is converted to differential voltage by the internal

I/V converter stage. The common-mode current sources balance the current at the amplifier summing node.

Figure 33. Main DAC Block Diagram

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