An345 – Cirrus Logic AN345 User Manual

Page 2

AN345

3. Converting a CS3302 design to use CS3302A

Systems originally designed using the CS3302 device can not use CS3302A transparently. To use the
CS3302A, the system designer needs to modify the system hardware by adding external 680

Ω anti-alias

filter resistors to replace the removed internal anti-alias filter resistors. Alternative resistor values may be
chosen to support other anti-alias RC filter configurations.

Figure 1 highlights an existing CS3302 design with a simple first-order anti-alias filter circuit constructed
between the CS3302 amplifier and the CS5371A modulator using internal CS3302 resistors.

Figure 1. CS3302 with a First-order Anti-alias Filter Using Internal Resistors

To use CS3302A, the simple addition of external 680

Ω anti-alias filter resistors is required to replace the

internal anti-alias filter resistors removed, as shown in Figure 2.

Figure 2. CS3302A with External Anti-alias Using External Resistors

640

diff

CS5371A

ΔΣ Modulator

INF+

INR+

INF-

INR-

INA+

INA-

640

diff

Programmable

GAIN

DIFFERENTIAL-MODE

CAPACITORS

CS3302 PROGRAMMABLE GAIN,

DIFFERENTIAL AMPLIFIER

GAIN0

GAIN1

GAIN2

To
Digital
Filter

INTERNAL ANTI-

ALIAS RESISTORS

OUTF+

OUTR+

OUTF-

OUTR-

680

diff

CS5371A

ΔΣ Modulator

INF+

INR+

INF-

INR-

INA+

INA-

680

diff

Programmable

GAIN

DIFFERENTIAL-MODE

CAPACITORS

CS3302A PROGRAMMABLE

GAIN, DIFFERENTIAL AMPLIFIER

GAIN0

GAIN1

GAIN2

To
Digital
Filter

EXTERNAL ANTI-

ALIAS RESISTORS

OUTF+

OUTR+

OUTF-

OUTR-