Cirrus Logic AN345 User Manual
Gain THD CS3302 THD CS3302A
1
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2 -119
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16 -118
32 -115
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AN345
Application Note
MIGRATING FROM THE CS3302 TO THE CS3302A
SEISMIC DIFFERENTIAL AMPLIFIER
1. SUMMARY
This document outlines the differences in operation of the CS3302A when compared to the CS3302
and explains how to use the CS3302A device in a system designed for the CS3302. In particular, the
need for external anti-alias filter resistors is addresse d.
2. DESCRIPTION OF CHANGES BETWEEN CS3302 AND CS3302A
The CS3302A seismic differential amplifier is a pin-compatible upgrade for the original CS3302 device.
The main purpose of the CS3302A revision is to provide a fix for the two CS3302 errata listed in errata
ER596A3 (items 1 and 2 in Table 1). In addition to this fix, further upgrades were implemented in the
CS3302A. Table 1 outlines the differences between the CS3302 and CS3302A.
Table 1: Differences Between CS3302 and CS3302A
Item Description
To achieve tighter anti-alias filter resistor tolerance, CS3302A eliminates intern al anti-alias filter resistors that exist in
CS3302 (specified in the CS3302 data sheet as 640 ohm ±10% depending on process paramete rs). This change
1
requires the CS3302A to use external anti-alias resistors.
Improved relative gain accuracy production test limits. CS3302A relative gain accuracy production test limits tight-
2
ened to ±0.2% maximum for all gain settings.
3
Removed unipolar power supply mode. CS3302A specified for bipolar power supply mode only.
4
Removed low power operating mode. CS3302A specified for normal power operati ng mode only.
5
CS3302A power supply specified operating limits tightened from ±5% to ±2%.
Improved typical THD performance by 1.0 dB, for gain ranges x2, x4, and x8.
10
Although the CS3302 and CS3302A are pin-compatible devices, the CS3302A is not a drop-in replace-
ment for the CS3302. Due to the removal of internal anti-alias filters, the CS3302A requires external antialias filter resistors to achieve optimum performance.
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SEP ‘10
AN345REV1
AN345
640
640
C
diff
CS5371A
ΔΣ Modulator
INF+
INR+
INF-
INR-
INA+
INA-
640
640
C
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
680
C
diff
CS5371A
ΔΣ Modulator
INF+
INR+
INF-
INR-
INA+
INA-
680
680
C
diff
Programmable
GAIN
DIFFERENTIAL-MODE
CAPACITORS
CS3302A PROGRAMMABLE
GAIN, DIFFERENTIAL AMPLIFIER
GAIN0
GAIN1
GAIN2
To
Digital
Filter
EXTERNAL ANTI-
ALIAS RESISTORS
OUTF+
OUTR+
OUTFOUTR-
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.
To use CS3302A, the simple addition of external 680 Ω anti-alias filter resistors is re quired to replace the
internal anti-alias filter resistors removed, as shown in Figure 2.
Figure 1. CS3302 with a First-order Anti-alias Filter Using Internal Resistors
Figure 2. CS3302A with External Anti-alias Using External Resistors
2
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