DAC38RF80 datasheet(72/155 Pages) TI1

72 / 155 page

coarsetrim

= 2mA × DACFS - 11

RBIAS

BIAS

0.9

128

3.6

RBIAS

coarsetrim

IOUT

SDIO

SCLK

TCLK

SLEEP

TXENABLE

TESTMODE

internal

digital in

VDDIO18

GND

SDENB

RESETB

TMS

TDI

TRSTB

internal

digital in

VDDIO18

GND

400

10 k

DAC38RF80, DAC38RF83, DAC38RF84

DAC38RF85, DAC38RF90, DAC38RF93

SLASEA3C – DECEMBER 2016 – REVISED JULY 2017

www.ti.com

DAC38RF83 DAC38RF93

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(1)

The bias current per each complementary output is half the total bias current

8.3.26 CMOS Digital Inputs

Figure 70 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.

Figure 70. CMOS Digital Equivalent Input

8.3.27 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:

(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:

(9)

The course trim current sources are configured through SPI register field DACFS in register DACFS (8.5.72),as

follows:

(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

(8.5.72), an extra DC bias current is required to set the operating point of the output current sources(Table 40).

Table 40. DAC output current

DACFS ( 8.5.72)

Signal current (mA)

Total bias current (mA)(1)

DAC38RF80 Datasheet(PDF) 72 Page - Texas Instruments

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