DAC38RF83IAAVR datasheet(70/160 Pages) TI2

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7.3.25 CMOS Digital Inputs

Figure 7-26 shows a schematic of the equivalent CMOS digital inputs of the DAC38RFxx. SDIO, SCLK, TCLK,

SLEEP, TESTMODE and TXENABLE have internal pull-down resistors while SDEN, RESET, TMS, TDI and

TRST have internal pull-up resistors. See the Specifications table for logic thresholds. The pull-up and pull-down

circuitry is approximately equivalent to 10 kΩ.

SDIO

SCLK

TCLK

SLEEP

TXENABLE

TESTMODE

internal

digital in

VDDIO18

GND

SDENB

RESETB

TMS

TDI

TRSTB

internal

digital in

VDDIO18

GND

400

10 k

Figure 7-26. CMOS Digital Equivalent Input

7.3.26 DAC Fullscale Output Current

The DAC38RFxx uses a bandgap reference and control amplifier for biasing the full-scale output current. The

DAC full scale output current is set by a combination of the fixed current through the external resistor RBIAS

(connected to pin BIASJ) and current from course trim current sources:

RBIAS

coarsetrim

IOUT

(8)

The bias current IBIAS through resistor RBIAS is defined by the on-chip bandgap reference voltage VBG

(nominally 0.9 V) and control amplifier. For normal operation, it is recommended that RBIAS is set to 3.6 kΩ

for a fixed current through RBIAS of 250 µA. This current is scaled 128x internally, giving:

RBIAS

BIAS

0.9

128

3.6

(9)

The course trim current sources are configured through SPI register field DACFS in register DACFS (7.5.72),as

follows:

coarsetrim

= 2mA × DACFS - 11

(10)

From the discussion above, the DAC full scale output current can be configured from 40 mA (DACFS[3:0] =

1111) down to 10 mA (DACFS[3:0] = 0000). In addition to the full scale signal current set by SPI register DACFS

(7.5.72), an extra DC bias current is required to set the operating point of the output current sources(Table 7-41).

Table 7-41. DAC output current

DACFS (7.5.72)

Signal current (mA)

Total bias current (mA)(1)

DAC38RF80, DAC38RF83, DAC38RF84

DAC38RF85, DAC38RF90, DAC38RF93

SLASEA3D – DECEMBER 2016 – REVISED DECEMBER 2023

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