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LTC1591/LTC1597

15917fa

Description

The LTC1591/LTC1597 are 14-/16-bit multiplying, current

output DACs with a full parallel 14-/16-bit digital interface.

The devices operate from a single 5V supply and provide

both unipolar 0V to – 10V or 0V to 10V and bipolar

±10V

output ranges from a 10V or –10V reference input. They

have three additional precision resistors on chip for bipo-

lar operation. Refer to the block diagrams regarding the

following description.

The 14-/16-bit DACs consist of a precision R-2R ladder for

the 11/13LSBs. The 3MSBs are decoded into seven seg-

ments of resistor value R. Each of these segments and the

R-2R ladder carries an equally weighted current of one

eighth of full scale. The feedback resistor RFB and

4-quadrant resistor ROFS have a value of R/4. 4-quadrant

resistors R1 and R2 have a magnitude of R/4. R1 and R2

together with an external op amp (see Figure 2) inverts the

reference input voltage and applies it to the 14-/16-bit DAC

input REF, in 4-quadrant operation. The REF pin presents

a constant input impedance of R/8 in unipolar mode and

R/12 in bipolar mode. The output impedance of the current

output pin IOUT1 varies with DAC input code. The IOUT1

capacitance due to the NMOS current steering switches

also varies with input code from 70pF to 115pF. An added

feature of these devices, especially for waveform genera-

tion, is a proprietary deglitcher that reduces glitch energy

to below 2nV-s over the DAC output voltage range.

Digital Section

The LTC1591/LTC1597 are 14-/16-bit wide full parallel

data bus inputs. The devices are double-buffered with two

14-/16-bit registers. The double-buffered feature permits

the update of several DACs simultaneously. The input

bus when the WR pin is brought to a logic low level. The

second register (DAC register) is updated with the data

from the input register when the LD pin is brought to a

logic high level. Updating the DAC register updates the

DAC output with the new data. To make both registers

transparent for flowthrough mode, tie WR low and LD

high. However, this defeats the deglitcher operation and

output glitch impulse may increase. The deglitcher is

activated on the rising edge of the LD pin. The versatility

of the interface also allows the use of the input and DAC

registers in a master slave or edge-triggered configura-

tion. This mode of operation occurs when WR and LD are

tied together. The asynchronous clear pin resets the

LTC1591/LTC1597 to zero scale and the LTC1591-1/

LTC1597-1 to midscale. CLR resets both the input and

DAC registers. These devices also have a power-on reset.

Table 1 shows the truth table for the LTC1591/LT1597.

Unipolar Mode

(2-Quadrant Multiplying, VOUT = 0V to – VREF)

The LTC1591/LTC1597 can be used with a single op amp

to provide 2-quadrant multiplying operation as shown in

Figure 1. With a fixed – 10V reference, the circuits shown

give a precision unipolar 0V to 10V output swing.

APPLICATIONS INFORMATION

Figure 1a. Unipolar Operation (2-Quadrant Multiplication) VOUT = 0V to – VREF

VCC

LTC1591

RFB

ROFS

RCOM

REF

0.1

μF

IOUT1

33pF

VOUT =

0V TO

–VREF

1591/97 F01a

AGND

DGND

10 TO 21,

24, 25

CLR

VREF

LT1001

14-BIT DAC

DATA

INPUTS

Unipolar Binary Code Table

DIGITAL INPUT

BINARY NUMBER

IN DAC REGISTER

–VREF (16,383/16,384)

–VREF (8,192/16,384) = –VREF/2

–VREF (1/16,384)

LSB

1111 1111

0000 0000

ANALOG OUTPUT

VOUT

MSB

1111

1000

0000

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