CDB5376 Ver la hoja de datos (PDF) - Cirrus Logic

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CDB5376

Multichannel Seismic Evaluation System

Cirrus Logic 

CDB5376

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.

Specification

Dual Series Switching Diode - ON Semiconductor

Surface Mount Package Type

Non-Repetitive Peak Forward Current (1 µs, 1 ms, 1 s)

Reverse Bias Leakage (25 C to 85 C)

Reverse Bias Capacitance (0 V to 5 V)

Value

BAV99LT1

SOT-23

2.0 A, 1.0 A, 500 mA

0.004 µA - 0.4 µA

1.5 pF - 0.54 pF

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 CS3301 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 CS3302 amplifier (CDB5376 channels 3 and 4), a differential low-

pass filter rejects high-frequency signals into the amplifier. The cutoff frequency for the low-pass filter is

high enough not to affect the magnitude response of the measurement bandwidth.

DS612DB2

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