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LTC2641/LTC2642

26412f

Power-On Reset

The LTC2641/LTC2642 include a power-on reset circuit

to ensure that the DAC ouput comes up in a known state.

When VDD is ﬁrst applied, the power-on reset circuit sets

the output of the LTC2641 to zero-scale (code 0). The

LTC2642 powers up to midscale (bipolar zero). Depend-

ing on the DAC number of bits, the midscale code is:

OPERATION

32,768 (LTC2642-16); 8,192 (LTC2642-14); or 2,048

(LTC2642-12).

Clearing the DAC

A 10ns (minimum) low pulse on the

⎯C⎯L⎯R pin asynchro-

nously clears the DAC latch to code zero (LTC2641) or to

midscale (LTC2642).

APPLICATIONS INFORMATION

Unipolar Conﬁguration

Figure 2 shows a typical unipolar DAC application for

the LTC2641. Tables 1a, 1b and 1c show the unipolar

binary code tables for 16-bit, 14-bit and 12-bit operation.

16-BIT DAC

1/2 LTC6078

5V/3V

VREF

2.5V

VDD

LTC2641-16

UNIPOLAR VOUT

0V TO 2.5V

4.7

μF

0.1

μF

REF

VOUT

GND

26412 F02

0.1

μF

0.1

μF

SCLK

DIN

CLR

LT®1019CS8-2.5

GND

OUT

The external ampliﬁer provides a unity-gain buffer. The

LTC2642 can also be used in unipolar conﬁguration by

tying RFB and INV to REF. This provides power-up and

clear to midscale.

Table 1b. 14-Bit Unipolar Binary Code Table

(LTC2641-14)

DIGITAL INPUT

BINARY NUMBER

IN DAC LATCH

ANALOG OUTPUT

(VOUT)

MSB

LSB

1111 1111 1111 11xx VREF (16,383/16,384)

1000 0000 0000 00xx VREF (8,192/16,384) = VREF/2

0000 0000 0000 01xx VREF (1/16,384)

0000 0000 0000 00xx 0V

Figure 2. 16-Bit Unipolar Output (LTC2641-16) Unipolar VOUT = 0V to VREF

Table 1a. 16-Bit Unipolar Binary Code Table

(LTC2641-16)

DIGITAL INPUT

BINARY NUMBER

IN DAC LATCH

ANALOG OUTPUT

(VOUT)

MSB

LSB

1111 1111 1111 1111 VREF (65,535/65,536)

1000 0000 0000 0000 VREF (32,768/65,536) = VREF/2

0000 0000 0000 0001 VREF (1/65,536)

0000 0000 0000 0000 0V

Table 1c. 12-Bit Unipolar Binary Code Table

(LTC2641-12)

DIGITAL INPUT

BINARY NUMBER

IN DAC LATCH

ANALOG OUTPUT

(VOUT)

MSB

LSB

1111 1111 1111 xxxx VREF (4,095/4,096)

1000 0000 0000 xxxx VREF (2,048/4,096) = VREF/2

0000 0000 0001 xxxx VREF (1/4,096)

0000 0000 0000 xxxx 0V

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