Cirrus Logic CRD5378 - Manual (Page 16)

CRD5378
16 DS639RD2
2.2.2 Differential Amplifiers
The CS3301A/02A amplifiers act as a low-noise gain stage for internal or external differential analog sig-
nals.
2.2.2.1 MCLK Input vs. GUARD Output
By default, CRD5378 uses the CS3302A hydrophone amplifier. The CS3302A amplifier is a very high in-
put impedance device and achieves a 1/f noise performance typically buried below the low-frequency
ocean noise. To minimize leakage from high impedance sensors connected to the CS3302A amplifier, pin
13 produces a GUARD signal output to actively drive a sensor cable shield with the common mode volt-
age of the sensor signal.
Comparing the CS3301A and CS3302A amplifiers, the functionality of pin 13 (MCLK input vs. GUARD
output) is the only external difference. The CS3301A amplifier is chopper-stabilized requiring a clock
source on input pin 13. In order to run the chopper circuitry synchronous to the modulator analog sampling
clock, the CS3301A amplifier pin 13 connects to the CS5378 digital filter (MCLK).
CRD5378 can be converted to use either the CS3301A and CS3302A amplifiers by installing the amplifier
device and populating R8, R9, and R10 with 0
Ω resistors accordingly.
Replacement amplifiers can be requested as samples from the local Cirrus Logic sales representative.
2.2.2.2 Rough-Fine Outputs - OUTR, OUTF
The analog outputs of the CS3301A/02A differential amplifiers are split into rough charge and fine charge
signals for input to the CS5373A
∆Σ modulator.
Analog Signals Description
INA Sensor analog input
INB Test DAC analog input
OUTR, OUTF Analog rough / fine outputs
GUARD CS3302A guard output (R10 = 0
Ω, R9 = NO POP)
Digital Signals
Description
MUX[0..1] Input mux selection
GAIN[0..2] Gain range selection
PWDN Power down mode enable
CLK CS3301A clock input (R10 = NO POP, R9 = 0
Ω)
Amplifier CS3301A CS3302A
U19 R8 + R9 *R10
Table 7. Amplifier Pin 13 Resistor Settings