HID I2C peripherals

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This topic describes the three required (and an optional fourth) power states for HID I2C peripherals.

HID I2C Peripheral Power States

State Mandatory/Optional Description Power Consumption (Recommendation)
ACTIVE Mandatory The fully active state of the device. 0.1 x Active Power Consumption + 0.9 x Idle Power Consumption <= 35 mW
IDLE Mandatory

The internal state of the device when there has been a period of inactivity. This period of inactivity should be 300 seconds.

Transitions in and out of this state are Device Initiated.

The device is required to meet the response latency requirements that are described in the Device.Digitizer.Touch.ResponseLatency requirement.

 0.1 x Active Power Consumption + 0.9 x Idle Power Consumption <= 35 mW
SLEEP Optional

Requires device implementing support for the SET_POWER command set of the HID I2C protocol.

In this state:

  • Interrupts de-asserted
  • Move to lowest power state Power down analog circuitry.
  • Must be able to respond to SET_POWER ON and transition to ACTIVE state without NACK.

Transitions in and out of this state are Host Initiated.

 <= 1mW
OFF Mandatory

The device will have no power applied in this state. The device must be able to transition between the OFF and ACTIVE states in <= 100ms – also known as maximum cold boot latency.

Transitions in and out of this state are Host Initiated.

 0mW

 

A system builder can choose one of two options for power management for a device:

  1. Implement a rail switching scheme for the touch controller.

  2. Require the optional SET_POWER functionality to be implemented for the device.

Note  These options are not mutually exclusive. However, the system builder will select an implementation that makes it possible to meet the Windows 8 system-on-a-chip (SOC) power requirements while minimizing hardware cost.

 

 

 

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