DAC7616EB datasheet(10/17 Pages) TI1

10 / 17 page

DAC7616

SBAS186

THEORY OF OPERATION

The DAC7616 is a quad, serial input, 12-bit, voltage output

DAC. The architecture is a classic R-2R ladder configuration

followed by an operational amplifier that serves as a buffer.

Each DAC has its own R-2R ladder network and output op

amp, but all share the reference voltage inputs. The minimum

voltage output (“zero-scale”) and maximum voltage output

(“full-scale”) are set by external voltage references (VREFL

and VREFH, respectively). The digital input is a 16-bit serial

word that contains the 12-bit DAC code and a 2-bit address

code that selects one of the four DACs (the two remaining

bits are unused). The converter can be powered from a single

+3V supply. Each device offers a reset function which imme-

diately sets all DAC output voltages and internal registers to

either zero-scale (code 000H) or mid-scale (code 800H). The

reset code is selected by the state of the RESETSEL pin

(LOW = 000H, HIGH = 800H). See Figure 1 for the basic

operation of the DAC7616.

ANALOG OUTPUTS

The output of the DAC7616 can swing to ground. Note that

the settling time of the output op amp will be longer with

voltages very near ground. Also, care must be taken when

measuring the zero-scale error. If the output amplifier has

a negative offset, the output voltage may not change for the

first few digital input codes (000H, 001H, 002H, etc.) since

the output voltage cannot swing below ground.

The behavior of the output amplifier can be critical in some

applications. Under short-circuit conditions (DAC output

shorted to VDD), the output amplifier can sink more current

than it can source. See the Specifications table for more

details concerning short-circuit current.

REFERENCE INPUTS

The minimum output of each DAC is equal to VREFL

plus a small offset voltage (essentially, the offset of

the output op amp). The maximum output is equal to

VREFH – 1LSB plus a similar offset voltage.

The current into the reference inputs depends on the DAC

output voltages and can vary from a few microamps to

approximately 0.4 milliamp. Bypassing the reference volt-

age or voltages with a 0.1

µF capacitor placed as close as

possible to the DAC7616 package is strongly recommended.

FIGURE 1. Basic Single-Supply Operation of the DAC7616.

NOTES: (1) U package pin configuration shown. (2) As configured, RESET LOW sets all internal registers

to code 000

H (0V). If RESETSEL is HIGH, RESET LOW sets all internal registers to code 800H (1.25V).

OUTD

OUTC

REFL

REFH

OUTB

OUTA

AGND

RESETSEL

RESET

LDAC

NIC

CLK

SDI

GND

Reset DACs(2)

Update Selected Register

Chip Select

Clock

Serial Data In

DAC7616(1)

0.1

µF

0.1

µF

0V to +1.25V

µF to 10µF

+3V

0V to +1.25V

+1.25V

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