L9700(1990) 데이터 시트보기 (PDF) - STMicroelectronics
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L9700 Datasheet PDF : 7 Pages
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L9700
Figure 2 : Dynamical Input Characteristics (continued) .
2b
APPLICATION INFORMATION
Most integrated circuits, both HNMOS and bipolar,
are very sensitive to positive and negative overvol-
tages on the supply and at the inputs.
These transients occur in large numbers and with
different magnitudes in the automotive environ-
ment, making adequate protection for devices ai-
med at it indispensible.
Overvoltages on the supply line are faced through
high voltage integration technologies or through ex-
ternal protection (transil, varistor).
Signal inputsare generally protected using clampdi-
odes to the supply and ground, and a current limi-ter
resistor. However, such solutions do not always
completely satisfy the protection specifications in
terms of intervention speed, negative clamping and
current leakage high enough to change analog si-
gnals.
The L9700 device combines a high intervention
speed with a high precision positive and negative
clamp and a low current leakage providing the opti-
mal solution to the problems of the automotive en-
vironment.
The high intervention speed, due to the pre-bias of
the limiter stage and internal feedback, limits the
voltage overshoot and avoid the use of external ca-
pacitors for the limitation of the transient rise times.
Figure 3 illustrates a typical automotive application
scheme. The resistor RS limits the input current of
the device and is therefore dimensioned consider-
ing the characteristics of the transients to be elimi-
nated. Consequently :
Vtransient Peak
RS = IIN MAX
The CIN capacitors must be used only on analog in-
puts because they present a low impedance during
the sampling period.
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