100k

100k

+

-

OUTx = 2 x DREF

(

)

DDATAx

1024

600

+

-

OUTx = DREF

(

)

DDATAx

1024

LMP92018

www.ti.com

SNAS514B – NOVEMBER 2011 – REVISED MAY 2013

The ideal DAC core transfer function from DATAx to OUTx , x=0...3, can be expressed as:

(3)

The above expression is subject to non-idealities of the resistor string and limitations of the output buffer. These

limitations are tabulated in Electrical Characteristics

In Figure 17, the PD (Power Down) signal is asserted when the given channel is disabled via the SPI command.

The PD causes the DAC buffer bias currents to shut down, and it breaks the current path through the resistive

string.

DAC Reference Selection

All DAC channels operate from the same, user selectable, reference source. In Figure 17, DREF input can be

supplied by the external source, applied to the REF pin of the device, or from the internal reference generator

block. The reference block functionality is described in INTERNAL VOLTAGE REFERENCE SOURCE.

Reference selection automatically forces configuration of the DACs' output buffers. If the external reference

source, which is DREF driven by the REF device pin, is selected then all of the DAC output buffers are in 1x

configuration, as seen inFigure 18. In the external reference mode, each active DAC presents a resistive load to

the source attached to the device's REF pin, see Figure 17 and Figure 21.

The overall DAC transfers function remains as shown in DAC Core

Figure 18. DAC Buffer when DREF Externally Supplied

If the internal reference generator is selected to drive the DAC's DREF input, then all of the DACs' buffers are

automatically forced into 2x gain configuration as shown in Figure 19. This results in an overall transfer function

of the DACs to change to:

(4)

Figure 19. DAC Buffer when DREF Internally Supplied

DIGITAL TEMPERATURE SENSOR

The local temperature sensor (TS) operates in one of the 2 possible modes: Continuous or One-Shot. The user

selects the mode of operation via the SPI instruction, see TEMPERATURE SENSOR CONFIGURE. The output

of the temperature sensor is a 12 bit signed integer, where each LSB represents 0.0625°C. Temperature

sensor's output code (TDATA) examples are shown in Table 1.

Copyright © 2011–2013, Texas Instruments Incorporated

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