Tiny SMT hermetic voltage references boast high stability


Tiny SMT hermetic voltage references boast high stability

Offering a high degree of long-term stability and consistent predictable behavior over time and operating conditions, the LS8 family of hermetic precision voltage references from Linear Technology target instrumentation applications that demand the best possible performance over years or decades of operation. Packaged in a 5mm x 5mm surface mount, low stress ceramic package, the LS8 package offers an alternative to large metal can or ceramic DIP packages. Mechanical stress on the internal die of a voltage reference frequently causes a shift in its output voltage. The LS8 package achieves superior stability, minimizing die stress in a number of ways. First, the LS8 is a hermetic package, which eliminates humidity effects. This significant and often unrecognized source of error is due to the absorption of water in non-hermetic plastic packaging. Typically, non-hermetic parts can experience 150ppm or more of error with 25% changes in relative humidity. In addition, the LS8 package has minimal direct die contact, reducing die stress from the package. In contrast, plastic molding applies stress directly to a silicon die over time and temperature. Because silicon and plastic have different thermal coefficients of expansion, temperature cycling a plastic part will apply inelastic stress to the die. The result is residual error, even when the part returns to 25°C. Similarly, a large component of long term drift error is due to the plastic package settling over time. All of this is significantly reduced in the LS8 reference family. "The LS8 package is a break-through for voltage references," says Brendan Whelan, design manager for Linear Technology. "Minimizing humidity, hysteresis and long term drift will minimize system calibration requirements. This should be welcome news for any precision equipment manufacturer." The LS8 reference family is based on four of Linear Technology's most popular precision voltage references, the LTC6655, LTC6652, LT6654 and LT1236. This includes a 5V buried Zener reference and three low dropout, 2.5V band-gap references. These voltage references cover a wide range of characteristics, including temperature drift from 2ppm/°C to 20ppm/°C, operation from -40°C to 125°C and low frequency noise down to 0.25ppm. Linear Technology