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AN229

Application Note

TRANSITIONING FROM THE CS8405A TO THE CS8406

by Sean Davis

1. Introduction

The CS8406 was designed as a pin and function compatible update for the CS8405A to add

192 kHz sample rate capability and offer over 1/3 less total power consumption than the

CS8405A. This document outlines the considerations that need to be accounted for when mak-

ing the transition. Please refer to the latest revision of each part’s datasheet for a detailed

description of part operation.

2. Power Supply

The VD+ supply of the CS8405A operates only at 5.0 V ±10%, while the VD supply of the

CS8406 operates at either 3.3 V or 5.0 V ±5%. However, when the CS8406 is operated with

VD = 5.0 V, certain conditions apply:

 V

(Min) for the CS8406 = 2.75 V. V

(Min) for the CS8405A = 2.0 V.

 In power down mode, it is recommended that all inputs be driven low to minimize current

consumption.

3. Software Mode

Shown in Table 2 on page 2 is a list of pin numbers and their corresponding pin names for both

parts when operated in Software mode. The register settings for the CS8405A are compatible

with the CS8406.

4. Hardware Mode

Shown in Table 3 on page 3 is a list of pin numbers and their corresponding pin names for both

parts when operated in Hardware mode.

5. CS8406 Test Pins

The CS8406 has several pins labeled as TEST. These pins are unused inputs in either Software

or Hardware mode. It is recommended that these pins be tied to a supply (VL or GND) to mini-

mize leakage current.

When transitioning from the CS8405A to the CS8406, some of the TEST pins on the CS8406

may be left floating due to corresponding pins on the CS8405A being labeled as no connects.

The CS8406 will operate the same if these pins are left floating, however current consumption

from VL will increase by 25 μA per pin that is left floating. As the CS8406 consumes much less

current than the CS8405A, this should not be a concern to the user.

APRIL ‘09

AN229REV2

Summary of content (4 pages)

PAGE 1
AN229 Application Note TRANSITIONING FROM THE CS8405A TO THE CS8406 by Sean Davis 1. Introduction The CS8406 was designed as a pin and function compatible update for the CS8405A to add 192 kHz sample rate capability and offer over 1/3 less total power consumption than the CS8405A. This document outlines the considerations that need to be accounted for when making the transition. Please refer to the latest revision of each part’s datasheet for a detailed description of part operation. 2.
PAGE 2
AN229 6. Output Resistance The typical output resistance of the transmitter pins changed from the CS8405A to the CS8406. The value of the external series resistor placed on the transmitter pins should be modified appropriately to account for this change. See the latest CS8406 datasheet for details on selecting the value of the external resistor. Parameter VL = 3.3 V TXP/TXN CS8405A Output Resistance TXP/TXN CS8406 Output Resistance VL = 5 V Unit 40 26 Ω 33.5 26.5 Ω Table 1.
PAGE 3
AN229 Pin Number CS8405A Pin Name CS8406 Pin Name Differences 2 VL2+ TEST See “CS8406 Test Pins” on page 1. 6 VD+ VD See “Power Supply” on page 1. 7 DGND4 TEST See “CS8406 Test Pins” on page 1. 8 DGND3 TEST See “CS8406 Test Pins” on page 1. HWCK0 Pins 20 and 27 set the OMCK clock ratio for the CS8406. Setting both pins to VL (the recommended setting from the CS8405A datasheet) or both pins to GND will cause the clock ratio to be 256*Fs, the only mode available for the CS8405A.
PAGE 4
AN229 7. Revision History Revision Changes REV1 Initial Release REV2 Added “Output Resistance” on page 2 . Contacting Cirrus Logic Support For all product questions and inquiries contact a Cirrus Logic Sales Representative. To find one nearest you go to www.cirrus.com IIMPORTANT NOTICE Cirrus Logic, Inc. and its subsidiaries ("Cirrus") believe that the information contained in this document is accurate and reliable.