SDI Technologies SDIO Card manual Power Control Overview, Power Control support for Sdio Cards

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SDIO Simplified Specification Version 2.00

11. Power Control

11.1Power Control Overview

The concept of high-power SDIO cards was introduced in Version 1.10 of the SDIO Specification. Power Control supports following two features:

•High-Power Support

SDIO cards created prior to Version 1.10 of the SDIO Specification were limited to a maximum current of 200mA at any time, irrespective of the number or types of functions supported. With the creation of wireless communication devices in the SDIO form factor, a need was seen to provide more current to accommodate the higher power requirements of some SDIO cards. Since backward compatibility is a primary concern for any changes made to this specification, a method was chosen to prevent a high-power card from drawing excessive amounts of current from hosts designed to only support the SDIO 1.0 cards. Master Power Control allows standard and high-power cards to be inserted into any host without causing excessive current damage to the host. It is important to note that there exists the possibility of trying to use a card that requires high-power in a standard power host and having that card fail to operate. Master Power Control is supported on a per card basis and available to the host in the CCCR. A high-power card may have a mix of both high and standard power functions.

•Power Selection Support

Not all hosts can supply enough current for all SDIO cards. A host may choose to use the SDIO card in a lower power mode to increase operation time. Power Selection enables the host to switch the card to a lower power mode. It is important to note that there exists the possibility of trying to use a standard power card in a host that does not have enough power to meet the card’s requirement. In this case the card will fail to operate. Cards supporting Power Selection will enable the widest range of host support. Power Selection is supported on a per function basis and available to the host in the FBR.

11.2Power Control support for SDIO Cards

11.2.1Master Power Control

SDIO version 1.10 cards indicate their support for the new power control functions with the SMPC (Support Master Power Control) bit in the CCCR (See section 6.9). Hosts enable the card’s power control functions with the EMPC (Enable Master Power Control) bit.

SMPC can be set to 0 if the card maximum current is less than 200mA and Power Selection (see section 11.2.2) is not supported. A SDIO version 1.10 card which has SMPC set to 1 shall maintain backward compatibility when EMPC is set to 0. A SDIO version 1.0 host may not be aware of EMPC, which will remain 0 (its default state).

In the case where EMPC is set to 0, the card total current shall not exceed 200mA. Functions that exceed 200mA shall not set IORx to 1 and TPLFE_OP_MAX_PWR shall be set to 0. If a multi-function card’s total power exceeds 200mA the card shall not set all IORx to 1, even if all IOEx are set to 1. Some of the functions’ IORx can be set to 1 as long as the card’s total current is less than 200mA. If the host tries to enable a function (IOEx =1) that will cause the card’s total current to exceed 200mA, the card shall disable (IORx=0) one or more functions to keep the card’s total current less than 200mA. Which functions are enabled depends on the design of the card vendor.

In the case where EMPC is set to 1, the card current can exceed 200mA, up to a maximum of 500mA. Card should be designed, where possible, to not require the maximum current , thus functioning in as many hosts as possible with sufficient power.

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