Integrated USB 2.0 Compatible 4-Port Hub

Datasheet

Chapter 6 Backward Compatibility to the USB20H04

The USB2504/USB2504A is pin compatible to the USB20H04, but is not designed to be a direct drop- in replacement. Many existing USB20H04 designs may accommodate a USB2504/USB2504A in place of the USB20H04, as long as specific Bill-Of-Material (BOM) modifications and population option changes are implemented. Since each design is unique, every customer considering a change from a USB20H04 to a USB2504/USB2504A should contact SMSC Applications Engineering for assistance.

6.1Internal 1.8V regulator

The USB2504/USB2504A has two internal 1.8V regulators that are enabled by default (ATEST pin contains an internal pull-up, and was specified as a No-Connect in the USB20H04 datasheet). Each regulator requires a separate 4.7uF Low ESR capacitor to ground. The USB20H04 designs that directly connect the Digital and Analog 1.8V pins together will not support a USB2504/USB2504A (unless the internal regulators are disabled).

6.2Configuration by Internal Defaults

The internal default settings that are loaded when this option is selected are very similar (but not identical) to those that were loaded in the USB20H04. The CFG_SEL[2:0] pins will properly select this method if the existing USB20H04 design was set-up to load the configuration via internal defaults.

The USB2504/USB2504A has pin strapping options that enable modification of the internal default load without requiring an EEPROM. The CFG_SEL2 pin (pin 59) on the USB2504/USB2504A was a VSS pin on the USB20H04 so this functionality will be disabled when a USB2504/USB2504A is placed into a USB20H04 design.

6.3Configuration by SMBus

The CFG_SEL[2:0] pins will properly select this method if the existing USB20H04 design was set-up to load the configuration via SMBus. The USB2504/USB2504A has a few additional registers, and has also moved some of the configuration bits so the actual SMBus code load itself will need to be modified. If a USB20H04 SMBus load is programmed into a USB2504/USB2504A, the results are unpredictable.

6.4PRTPWR_POL

The USB2504/USB2504A has a new strapping option that enables the port power control active state to be either active-high or active-low. The USB20H04 only provided active-low port power control. The PRTPWR_POL pin on the USB2504/USB2504A is pin 23, which was a VSS pin on the USB20H04, so by default, a USB20H04 design will select active-low port port control.

SMSC USB2504/USB2504A

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Revision 2.3 (08-27-07)

 

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