The SN75976A is an improved replacement for the industry's first 9-channel RS-485 transceiver -- the SN75LBC976. The A version offers improved switching performance, a smaller package, and higher ESD protection. The SN75976A is offered in two versions. The '976A2 skew limits of 4 ns for the differential drivers and 5 ns for the differential receivers complies with the recommended skew budget of the Fast-20 SCSI standard for data transfer rates up to 20 million transfers per second. The '976A1 supports the Fast SCSI skew budget for 10 million transfers per second. The skew limit ensures that the propagation delay times, not only from channel-to-channel but from device-to-device, are closely matched for the tight skew budgets associated with high-speed parallel data buses.
The patented thermal enhancements made to the 56-pin shrink small-outline package (SSOP) of the SN75976 have been applied to the new, thin shrink, small-outline package (TSSOP). The TSSOP package offers even less board area requirements than the SSOP while reducing the package height to 1 mm. This provides more board area and allows component mounting to both sides of the printed circuit boards for low-profile, space-restricted applications such as small form-factor hard disk drives.
In addition to speed improvements, the '976A can withstand electrostatic discharges exceeding 12 kV using the human-body model, and 600 V using the machine model of MIL-PRF-38535, Method 3015.7 on the RS-485 I/O terminals. This is six times the industry standard and provides protection from the noise that can be coupled into external cables. The other terminals of the device can withstand discharges exceeding 4 kV and 400 V respectively.
Each of the nine channels of the '976A typically meet or exceed the requirements of EIA RS-485 (1983) and ISO8482-1987/TIA TR30.2 referenced by American National Standard of Information (ANSI) Systems, X3.131-1994 (SCSI-2) standard, X2.277-1996 (Fast-20 Parallel Interface), and the Intelligent Peripheral Interface Physical Layer-ANSI X3.129-1986 standard.
The SN75976A is characterized for operation over an ambient air temperature range of 0°C to 70°C. The SN55976A is characterized for operation over an ambient air temperature range of -55°C to 125°C.
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