SN74AXC4T774: How many device can be drive??

Gordon Liu

Intellectual 855 points

Part Number: SN74AXC4T774
Other Parts Discussed in Thread: SN74AUC34, SN74AUC2G34

Hi,

I want use a SN74AXC4T774PW to drive many SPI device.

How many device can be drive??

System spec.:

1: level shift 3.3V => 1.2V

2: use the many SPE_CS pin to select each chip

3: MCU_SPI_CLK, MCU_SPI_DO connect to many chip parallel

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 317260 points

The output impedance of the driver, the trace resistance, and the capacitance of the traces and the devices form low-pass filters that limit the speed of rising/falling edges. (See [FAQ] What is the output transition rate for a logic device?)

If you have an estimate for these values, you can compare against the input rise/fall rate requirements of your SPI devices and the frequencies that you want to use.

If in doubt, you can insert more buffers (for 1.2 V, use the AUC logic family, e.g., SN74AUC2G34, SN74AUC34).

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SN74AXC4T774: How many device can be drive??