12-bit DAC in TSOT-23 Includes Bidirectional REF Pin for
Connection to Op Amp or External High Precision Reference
Design Note 448
Kevin Wrenner, Troy Seman and Mark Thoren
Introduction
The LTC®2630’s combination of a 12-bit DAC and low-drift
integrated reference in a tiny SC-70 package has proven
popular for a wide variety of applications. Two new DACs,
the LTC2631 and LTC2640, take this winning formula and
further expand its reach by adding a bidirectional REF pin
and an optional I2C interface in a tiny TSOT-23. The LT1991 precision op amp is a superb choice for
amplifying or attenuating the DAC output to achieve a
desired output range because it requires no precision
external resistors. Its integrated, precision resistors are
matched to 0.04%, allowing gain to be set by simple pin
strapping (see the data sheet for a large variety of gain
options). Figure 1 shows the configuration for a difference
gain of 4, resulting in a В±5V output with 12-bit programmability under I2C control. Integral nonlinearity, seen in
Figure 2, is better than 1LSB. Like their predecessor, these parts feature 1-bit INL and
DNL, offer excellent load regulation driving up to 10mA
loads, and can operate rail-to-rail. See Table 1 for a list
of options. Figure 3 shows a negative output system using a similar
setup, this time with the LT1991 conп¬Ѓgured as an inverting …