Cirrus Logic CRD5376 - Manual (Page 13)

CRD5376
DS612RD2 13
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.
Once a voltage spike is shunted to the power supply rail, a discharge path to ground must be present or
the power supply will itself spike. Transient voltage suppressors clamp the ±2.5 V analog supply rails in
the event of a voltage spike.
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 using the CS3301A amplifier (CRD5376 channels 1 and 2), the INA input has a com-
mon-mode and differential-mode 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-mode 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 (CRD5376 channels 3 and 4), the inherent ca-
pacitance of the piezoelectric sensor is connected to the INA sensor inputs and combined with large dif-
ferential-mode resistors (412 k
Ω + 2 kΩ) to create an analog high-pass RC filter. Assuming a hydrophone
group capacitance of 128 nF, the high-pass RC filter cut-off frequency is 3 Hz and eliminates the low-fre-
quency components of ocean noise. In addition to high-pass filtering, the 2 k
Ω resistor serves as a current-
limiting resistor to protect the amplifier inputs against transient voltage spikes.
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
Specification Value
Dual Surface Mount TVS - Diodes Inc.
MMBZ5V6AL-7
Surface Mount Package Type SOT-23
Working Voltage, Leakage Current 3.0 V, 5 µA
Breakdown Voltage, Threshold Current 5.6 V, 20 mA
Clamp Voltage, Peak Current 8.0 V, 3.0 A