Cirrus Logic CRD5378 - Manual (Page 14)

CRD5378
14 DS639RD2
2.2.1.4 Input Protection
Sensor inputs must have circuitry to protect the analog electronics from voltage spikes. Geophone coils
are susceptible to magnetic fields (especially from lightning) and hydrophones can produce large voltage
spikes if located near an air gun source.
Discrete switching diodes quickly clamp the analog inputs to the power supply rails when the input voltage
spikes. These diodes are reverse biased in normal operation and have low reverse bias leakage and ca-
pacitance characteristics to maintain high linearity on the analog inputs.
2.2.1.5 Input RC Filters
Following the diode clamps is an RC filter network that bandwidth limits the sensor inputs into the ampli-
fiers to 'chop-the-tops-off' residual voltage spikes not clamped by the discrete diodes. In addition, all Cir-
rus Logic component ICs have built in ESD protection diodes guaranteed to 2000 V HBM / 200 V MM
(JEDEC standard). The small physical size of these ESD diodes restricts their current capacity to 10 mA.
For land applications that use the CS3301A amplifier, the INA input has a common mode and differential
RC filter. The common mode filter sets a low-pass corner to shunt very high frequency components to
ground with minimal noise contribution. The differential filter sets a low-pass corner high enough not to
affect the magnitude response of the measurement bandwidth.
For marine applications that use the CS3302A amplifier, the inherent capacitance of the piezoelectric sen-
sor is combined with large resistors to create an analog high-pass RC filter to eliminate the low-frequency
components of ocean noise.
Specification Value
Dual Series Switching Diode - ON Semiconductor
BAV99LT1
Surface Mount Package Type SOT-23
Non-Repetitive Peak Forward Current (1
µs, 1 ms, 1 s)
2.0 A, 1.0 A, 500 mA
Reverse Bias Leakage (25 C to 85 C) 0.004
µA - 0.4 µA
Reverse Bias Capacitance (0 V to 5 V) 1.5 pF - 0.54 pF