DAC7678SPW datasheet(24/57 Pages) TI2

24 / 57 page

REF

Reference

Disable

DAC7678

SBAS493C – FEBRUARY 2010 – REVISED JANUARY 2014

www.ti.com

INTERNAL REFERENCE

which consists of 8 bit Address Byte plus 24 bit serial

command as shown in Table 1. During the time that

The DAC7678 includes a 2.5V internal reference that

the internal reference is disabled, the DAC functions

is disabled by default. The internal reference is

normally using an external reference. However, when

externally available at the VREFIN/VREFOUT pin. A

switching to the external reference the internal gain is

minimum 100nF capacitor is recommended between

dynamically switched to one. Therefore appropriate

the reference output and GND for noise filtering. The

value of external reference should be used per the

internal reference of the DAC7678 is a bipolar-

desired output voltage. At this point, the internal

transistor based precision bandgap voltage reference.

reference is disconnected from the VREFIN/VREFOUT pin

Figure 88 shows the basic bandgap topology.

(3-state

output).

not

attempt

drive

the

Transistors Q1 and Q2 are biased such that the

VREFIN/VREFOUT pin externally and internally at the

current density of Q1 is greater than that of Q2. The

same time indefinitely. There are two modes that

difference of the two base-emitter voltages (VBE1 –

allow communication with the internal reference:

VBE2) has a positive temperature coefficient and is

Regular/Static and Flexible. In Flexible mode DB14

forced across resistor R1. This voltage is gained up

needs to be set to '1' as shown in Table 17.

and added to the base-emitter voltage of Q2, which

has a negative temperature coefficient. The resulting

Regular/Static Mode (see Table 1 and Table 2)

output voltage is virtually independent of temperature.

The short-circuit current is limited by design to

Enabling Internal Reference:

approximately 100mA.

To enable the internal reference, write the 24-bit

serial command shown in Table 1 after properly

addressing the device. When performing a power

cycle to reset the device, the internal reference is

switched off (default mode). In the default mode, the

internal reference is powered down until a valid write

sequence is applied to power up the internal

reference. Setting DB4 to '1' turns on the internal

reference.If the internal reference is powered up, it

automatically powers down when all DACs power

down in any of the power-down modes (see Table 17

and Power Down Modes section). The internal

reference automatically powers up when any DAC is

powered up.

Disabling Internal Reference:

To disable the internal reference, address the device

by writing the 8-bit address byte and then writing the

24-bit serial command shown in Table 1. When

performing a power cycle to reset the device, the

Figure 88. Simplified Schematic of the Bandgap

internal reference is put back into the default mode

Reference

(switched off).

SPACER

Enable/Disable Internal Reference

The internal reference in the DAC7678 is disabled by

default for debugging, evaluation purposes, or when

using an external reference. The internal reference

can be powered up and powered down using a serial

command that requires a 32-bit write sequence,

Table 1. Write Sequence for Enabling Internal Reference (Static Mode) (Internal Reference Powered On)

COMMAND AND ACCESS BYTE

MOST SIGNIFICANT DATA BYTE

LEAST SIGNIFICANT BYTE

DB15

DB14

DB13

DB12

DB11

DB10

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

Table 2. Write Sequence for Disabling Internal Reference (Static Mode) (Internal Reference Powered Off)

COMMAND AND ACCESS BYTE

MOST SIGNIFICANT DATA BYTE

LEAST SIGNIFICANT BYTE

DB15

DB14

DB13

DB12

DB11

DB10

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

Submit Documentation Feedback

Product Folder Links: DAC7678

DAC7678SPW Datasheet(PDF) 24 Page - Texas Instruments

DAC7678SPW Datasheet(HTML) 24 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

Datasheet Download

Link URL