DAC1282IPW datasheet(15/43 Pages) TI1

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COM + VDIFF/2

COM

VOUTP

VOUTN

COM + VDIFF/2

COM - VDIFF/2

DAC1282

Output Frequency (Hz)

(1)

M[3:0] + 1

N[7:0] + 1

250

FREQ

DAC1282

www.ti.com

SBAS490

– DECEMBER 2011

SIGNAL OUTPUT (VOUTP, VOUTN)

As shown in Figure 34, the DAC provides a differential voltage (VDIFF = VOUTP – VOUTN) on pins VOUTP and

VOUTN. The output common-mode voltage (VCOM) is regulated to 100 mV below the midpoint of the analog

supply (AVDD

– AVSS).

Each signal output swings above and below the common-mode voltage. Best performance is realized when the

DAC output is used differentially. In power-down mode, the outputs enter a high-impedance, 3-state mode.

NOTE: VDIFF = VOUTP – VOUTN = ±2.5 V × Gain (VREF = 5 V).

VCOM = –0.1 V (±2.5-V supplies) or 2.4 V (5-V supply).

Figure 34. DAC Output Signal

The DAC output buffer is rated to drive up to a 2-nF capacitive load (maximum) and a 100-

Ω resistive load

(minimum). However, degradation of THD performance results in resistive loads less than 1 k

Ω, as shown in

Figure 26

The internal digital modulator generates the signal to drive the DAC. The modulator shapes the in-band noise to

high frequency and the frequency-shaped noise is present on the DAC output. However, the high frequency DAC

output noise is rejected by the digital filter of the ADC and does not affect system performance.

DAC MODES

The DAC1282 has four operational modes of: sine, dc, pulse, and external digital data input. These modes are

programmed by the MODE[1:0] bits in the GANMOD register, as shown in Table 1.

Table 1. DAC Modes

MODE[1:0] BITS

DAC MODE

Sine

Digital data

Pulse

Sine Mode

In sine mode, the DAC1282 provides a sine-wave output. An internal signal generator develops the sine-wave

signal. The M[3:0], N[7:0], and FREQ register bits program the output frequency. The frequency range is

programmable from 0.4883 Hz to 250 Hz, as shown in Equation 1.

where:

M[3:0]

≤ N[7:0]

(1)

fCLK = 4.096 MHz. The signal frequency scales with fCLK.

(1)

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