DAC7724N datasheet(13/21 Pages) TI1

13 / 21 page

DAC7724, 7725

ANALOG OUTPUTS

When VSS = –15V (dual supply operation), the output

amplifier can swing to within 4V of the supply rails, guar-

anteed over the –40

°C to +85°C temperature range. With

VSS = 0V (single-supply operation) and RLOAD connected to

ground, the output can swing to ground. Note that the

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

voltages very near ground. Additionally, care must be taken

when measuring the zero-scale error when VSS = 0V. Since

the output voltage cannot swing below ground, the output

voltage may not change for the first few digital input codes

(000H, 001H, 002H, etc.) if the output amplifier has a nega-

tive offset. At the negative offset limit of –4 LSB (-9.76mV),

for the single-supply case, the first specified output starts at

code 004H.

REFERENCE INPUTS

For dual-supply operation, the reference inputs, VREFL and

VREFH, can be any voltage between VSS + 4V and VCC – 4V

provided that VREFH is at least 1.25V greater than VREFL.

For single-supply operation (VSS = 0V), VREFL value can be

above 0V, with the same provision that VREFH is at least

1.25V greater than VREFL. The minimum output of each

DAC is equal to VREFL plus a small offset voltage (essen-

tially, the offset of the output op-amp). The maximum

output is equal to VREFH plus a similar offset voltage. Note

that VSS (the negative power supply) must either be con-

nected to ground or must be in the range of –14.25V to

–15.75V. The voltage on VSS sets several bias points within

the converter, if VSS is not in one of these two configura-

tions, the bias values may be in error and proper operation

of the device is not guaranteed.

The current into the VREFH input and out of VREFL depends

on the DAC output voltages and can vary from a few

microamps to approximately 0.3mA. The reference input

appears as a varying load to the reference. If the reference

can sink or source the required current, a reference buffer is

not required. See “Reference Current vs Code” in the Typi-

cal Performance Curves.

The analog supplies (or the analog supplies and the refer-

ence power supplies) have to come up first. If the power

supplies for the references come up first, then the VCC and

VSS supplies will be “powered from the reference via the

ESD protection diodes” (see page 4).

Bypassing the reference voltage or voltages with at least a

0.1uF capacitor placed as close to the DAC7724/25 package

is strongly recommended.

FIGURE 3. Basic Dual-Supply Operation of the DAC7724/25.

REFH

OUTB

Load DAC Registers

Reset DACs(1)

OUTA

GND

RESET

LDAC

DB0

DB1

DB2

DB3

DB4

DB5

DB6

REFL

OUTC

DAC7724

DAC7725

OUTD

R/W

DB11

DB10

DB9

DB8

DB7

Chip Select

–10V to +10V

Read/Write

Data Bus

Address Bus

or Decoder

NOTE: (1) Reset LOW sets all DACs to code 800

H on the DAC7724 and to code 000H on the DAC7725.

–10.000V

0.1

µF

–10V to +10V

–15V

+10.000V

0.1

µF

0.1

µF

µF to 10µF

Data Bus

+15V

0.1

µF

µF to 10µF

+5V

0.1

µF

µF to 10µF

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