Main

DAC

Serial

Interface

CS

SCLK

DIN

DOUT

Sine Wave

Generator

24-Bit

DC Register

Pulse

Registers

Digital

Modulator

CLK

RESET/PWDN

SYNC

SW/TD

Pulse

DAC

Differential

Switch

Synchronization

SYNC

Current

Generator

Analog Gain Control

Switch Control/Bitstream Input

VOUTP

VOUTN

CAPP

SWOUTP

SWOUTN

SWINN

SWINP

DVDD

AVDD

DGND

DAC1282

VREF

CAPN

AVSS

Buffer

DAC1282

www.ti.com

SBAS490

– DECEMBER 2011

OVERVIEW

The DAC1282 is a single-chip, digital-to-analog converter (DAC) that self-generates low-distortion sine-wave and

pulse-output signals for the demanding testing requirements of seismic recording equipment. Figure 32 shows

the block diagram of the DAC1282.

The DAC1282 requires two supply voltages: analog and digital. The analog supply can be single 5 V or bipolar

±2.5 V. The digital supply range is 1.65 V to 3.6V. The output signal common-mode voltage is regulated to

100 mV below the midpoint of the analog power-supply voltage. An internal power-on reset (POR) circuit resets

the DAC on power-up.

An SPI

™-compatible serial interface is used to access the DAC1282 registers for device configuration and

control. The configuration registers can be read back by clocking the data out on the DOUT pin. The DAC1282

voltage output is fully differential and is taken out on the VOUTP/VOUTN pins. The CAPP/CAPN pins connect to

external filter capacitors to reduce the output noise.

The reference input voltage sets the DAC1282 full-scale output. The DAC reference voltage is applied between

the VREF and AVSS pins. The DAC is optimized to operate with a 5-V reference. The sine-wave generator is

programmable by registers to set the sine frequency and amplitude. The frequency range is programmable from

0.4883 Hz to 250 Hz. The output level is controlled by both analog gain (in 6-dB steps), and digital gain (in

0.5-dB steps).

Figure 32. DAC1282 Block Diagram

The digital modulator takes the output from the sine-wave generator or the 24-bit dc register to generate the

ones-density bitstream. The bitstream drives the main DAC. Optionally, ones-density data can be input to drive

the DAC directly, bypasses the digital signal generator. The main DAC develops a differential output current that

is converted to a differential output voltage by an internal current-to-voltage (I/V) amplifier. The output range is

set by analog gain that scales the DAC current generator. The output amplifier provides current limit protection.

The dc mode is programmed by a 24-bit register and is used to provide a dc output. The dc mode also has

programmable ranges controlled by the analog gain control.

In Pulse mode, a fast-response, 5-bit pulse DAC is used to provide 31 preset dc levels. The levels span over the

available output ranges. The pulse DAC is optimized to provide fast response with short output rise times. The

pulse DAC is triggered by the SYNC pin for precision control of the pulse time.

The DAC1282 includes a low distortion differential output switch. The output switch can connect the DAC1282

output to sensors for THD and impulse testing. The switch is controlled by either pin or command, thus allowing

precise switch timing.

Copyright

© 2011, Texas Instruments Incorporated

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