Cirrus Logic CDB5376 - Manual (Page 17)

CDB5376
DS612DB3 17
2.2.1.3 Internal Inputs - DAC_OUT, DAC_BUF
The CS4373A test DAC has two high-performance differential test outputs, a precision output
(DAC_OUT) and a buffered output (DAC_BUF). These test outputs can be connected to the INA or INB
inputs of any channel through the input selection jumpers.
By default, CDB5376 is populated with passive RC filter components on the INA inputs, and no filter com-
ponents on the INB inputs (though the component footprints are present on the INB inputs). Because the
CS4373A precision output will not tolerate significant loading, on CDB5376 the DAC_OUT signal should
only jumper to the INB inputs. The CS4373A buffered outputs are less sensitive to the RC filter load and
DAC_BUF can be jumpered to either the INA or INB inputs.
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 Cirrus
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 (CDB5376 channels 1 and 2), the INA input has a com-
mon 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-frequen-
cycomponents 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