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What Are the Signal and Power Capabilities of the Cheetah SPI Host Adapter?
Rena Ayeras

Photograph by Magda Ehlers

Photograph by Magda Ehlers

Question from the Customer:
I plan to use the Cheetah SPI Host Adapter in a post-silicon validation. Before I start running validation tests, can you tell me what to expect from the power and signal pins?

Response from Technical Support:

Thanks for your question! The Cheetah SPI Host Adapter is designed to work at high speed directly with TTL and CMOS devices. The following sections provide the information that you requested.

Overview of SPI Signals

Here is an overview of how the Cheetah adapter signals work.

  • When the Cheetah adapter is enabled, all Cheetah SPI signals, SS0-2, MOSI, MISO, SCLK, are active at the same time.
  • If the MISO pin of your target device goes to a tri-state condition between transactions, a weak pull-up resistor can be used on the MISO line to stabilize the logic level.
  • The Cheetah adapter output pins have a drive strength of up to 10mA, which enables the SCLK signal to drive up to 10mA. If more current is needed by the slave load, a buffer can be added.

Power and Voltage Levels

The following sections describe the power and signal I/O of the Cheetah host adapter.

Power Supply Pins

Cheetah adapter Pins 4 and 6 (NC/+5V) can provide +5V power to the target system. You can enable these signals with our software tools, Control Center Serial Software, Flash Center Software, and Cheetah Software API, each of which you can download for free.

Signal Levels Support TTL and CMOS Devices

The Cheetah adapter voltage level is 3.3V and  is compatible with 5V voltage level devices. The signal levels should be nominally 3.3 volts (+/- 10%) logic high. This level allows the Cheetah adapter to be used with both TTL (5 Volt) and CMOS logic level (3.3 volt) devices. If you need to work with other signal levels, we have a solution for that in the section about guidelines.

Minimum and maximum voltage levels for SPI I/O signals:

  • VIH: min: 2V, max: 5.5V
  • VIL: min: 0V, max: 0.8V
  • VOH: min: 2.4
  • VOL: max: 0.4V

Current levels for SPI I/O signals:

  • Up to 25mA for each +5V pin
  • Up to 10 mA current source or sink for each SPI signal

Pull-up and pull-down resistors for output signals:

  • When the output signals are enabled, there are no pull-up or pull-down resistors on the Cheetah SPI signals. Instead, the Cheetah adapter actively drives the lines.
  • When the outputs are disabled, there are very weak pull-up / pull-down resistors of 20k Ohm on the Cheetah SPI signals. The Cheetah adapter keeps the last state of the lines.

Input capacitance and the input leakage current:

  • Cheetah adapter SPI signals I/O capacitance: 10 p F (1 MHz).
  • Cheetah adapter SPI signals input leakage current: +/- 10 uA.

Guidelines for Other Technical Requirements

If the signal levels of the target device are incompatible with Cheetah adapter specifications, the Level Shifter Board could support your project. For more information, take a look at Support Question of the Week: How Do I Use the Cheetah SPI Host Adapter with a 1.8V Flash Device and Adjust the Timing?

Sometimes you need to quickly provide test signals. The Cheetah adapter does not provide GPIO pins, but here is a work-around that has helped others. For more information, take a look at Support Question of the Week: How Can a GPIO Interface be Created for the Cheetah SPI Host Adapter to Control the Reset Signal and Pulse Periods?

We hope this answers your questions. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.