73S8009CN Datasheet, PDF (17/30 Pages) Teridian Semiconductor Corporation – Combo ISO-7816 and USB Universal Smart Card Interface IC

DS_8009CN_026
73S8009CN Data Sheet
Important Notes:
1. When the host is not powered by the V_DD supply of the 73S8009CN, special care must be taken
as the host signals going to the 73S8009CN can be active when the device is powered OFF.
This can create issues such as excessive current drain on the control signals and potentially
prohibit proper turn ON of the 73S8009CN. Series resistors on the input signals (except the
ON/OFF input) are recommended to provide isolation and prevent any potential problems.
The recommended value of these resistors is 47kΩ. It is also necessary for the host to set
these input signals to the low state (except for ON/OFF) when the 73S8009CN is OFF. False
activation of the card is possible if the CMDVCC# or CMDVCC% inputs are low (with a card
inserted) when the 73S8009CN is powered ON. For this reason, the proper sequencing of the
73S8009CN is required. The CMDVCC# or CMDVCC% inputs must be set high immediately
before the ON/OFF input is taken low to turn on the 73S8009CN. The time between setting the
CMDVCC# or CMDVCC% inputs high and the setting of the ON/OFF input set low should be
kept to a minimum as the CMDVCC# or CMDVCC% inputs, when set high with the 73S8009CN
OFF, will draw significant current under these conditions. The 47kΩ series resistors will
mitigate this current draw. However, some additional current will be drawn through the
resistors to the CMDVCC# or CMDVCC% inputs during this time so it should be kept to a
minimum.
2. For applications where ON/OFF is controlled by the host, the OFF_REQ and OFF_ACK signals do
not need to be connected to the host. When the OFF_ACK pin is left unconnected, the 73S8009CN
will turn off properly by the action of the internal resistor connection to OFF_REQ.
3. If the host is capable of selectively monitoring the I/O line, it can be used in place of the V_DD supply
monitor as it is tied to the V_DD supply through a pull up resistor when the smart card interface is not
activated.
4. When the 73S8009CN is powered OFF, the host will not be able to detect a card event (card
insertion/removal). If this function is necessary, then the host must monitor the card connector switch
separately.
5. For systems that do not use VDD to power the host controller, the host interface signals must operate
at 3.3V as the 73S8009CN digital logic operates off the V_DD (3.3V) supply regardless of the value of
the V_PC supply.
6. The ON/OFF pin is internally pulled up to V_PC through a 24kΩ resistor. Special care must be taken if
the host signal controlling the ON/OFF signal is running at a voltage different from V_PC. If this is the
case, then either the host control signal must be a maximum V_PC supply tolerant open drain output or
an external circuit should provide some isolation between the host control signal and the ON/OFF pin.
7. For those systems that require low power operation or are battery operated, the host controller circuit
firmware should place the 73S8009CN in the OFF state if no card activity is required.
Rev. 1.4
17