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AS1716

Datasheet - Detailed Descr i p ti on

8 Detailed Description

Sensor Biasing and Input Protection Resistors

Due to the capacitive and differential nature of the knock sensor, the common mode voltage for the sensor must be set. This is ensured by the

first amplifier, whose virtual ground is biasing the sensor via a of 50k

Ω resistor. Due to a failure, voltages up to 16V can occur on the input pins.

In this case two external serial resistors of 1k

Ω must be applied at the inputs. These resistors are limiting the current, when the on chip protec-

tion diode opens.

Figure 9. Sensor Biasing

Inverting Input Structure

The Input Strucutre is a first order low-pass filter and fulfills two main functions. First, it is used for biasing the sensor and second, the first order

low-pass filter characteristic is used for noise suppression.

Figure 10. Input Buffer

Due to

failure

up to 16V

typical

sensor

1k

1k

INN

INP

+

-

VDDA

VDDA/2

-

+

VDDA/2

-

+

VDDA/2

-

+

VDDA/2