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FIGURE 4b Automatic Offset

Adjustment Using LMC669

In very critical applications where a manual adjustment is

impractical the LMC669 Auto Zero circuit may be used to

reduce the effective input offset voltage to around 5

mVas

in

plifiers in an auto zero loop because its fast settling capabil-

ity keeps its summing node voltage more stable Therefore

the LMC669 is able to more accurately sample the summing

node voltage before making an offset correction

Input Bias Current

The JFET input stage of the LF400 ensures low input bias

current (200 pA maximum) when the die is at room tempera-

ture but this current approximately doubles for every 10 C

increase in temperature In applications that demand the

lowest possible input bias current a heat sink should be

used with the LF400 ‘‘Press on’’ heat sinks from manufac-

turers such as Thermalloy and AAVID can reduce junction

temperature by roughly 10 Cto40 C

Typical Applications

High-Speed DAC with Voltage Output

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