73S8023C 查看數據表（PDF） - Teridian Semiconductor Corporation

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73S8023C

Smart Card Interface

Teridian Semiconductor Corporation 

DS_8023C_019

73S8023C Data Sheet

5 Voltage Supervision

Two voltage supervisors constantly check the presence of the voltages VDD and VCC. A card deactivation

sequence is triggered upon a fault detected by these voltage supervisors.

The digital circuitry is powered by the power supply applied on the VDD pin. VDD also defines the voltage

range for the interface with the system controller. The VDD Voltage supervisor is also used to initialize the

ISO-7816-3 sequencer at power-on, and also to deactivate the card at power-off or upon a fault. The

voltage threshold of the VDD voltage supervisor is internally set by default to 2.3 V nominal. However, it

may be desirable, in some applications, to modify this threshold value. The pin VDDF_ADJ (pin 17) is

used to connect an external resistor REXT to ground to raise the VDD fault voltage to another value, VDDF.

The resistor value is defined as follows:

REXT = 180 kΩ /(VDDF - 2.33)

An alternative (more accurate) method of adjusting the VDD fault voltage is to use a resistive network of

R3 from the pin to supply and R1 from the pin to ground (see Figure 11: 73S8023C – Typical Application

Schematic). In order to set the new threshold voltage, the equivalent resistance must be determined.

This resistance value will be designated Kx. Kx is defined as R1/(R1+R3). Kx is calculated as:

Kx = (2.649 / VTH) - 0.6042 where VTH is the desired new threshold voltage.

To determine the values of R1 and R3, use the following formulas:

R3 = 72000 / Kx

R1 = R3*(Kx / (1 – Kx))

Taking the example above, where a VDD fault threshold voltage of 2.7 V is desired, solving for Kx gives:

 Kx = (2.649 / 2.7) - 0.6042 = 0.377

Solving for R3 gives:  R3 = 72000 / 0.377 = 191 kΩ.

Solving for R1 gives:  R1 = 191000 *(0.377 / (1 – 0.377)) = 115.6 kΩ.

Using standard 1 % resistor values gives R3 = 191 kΩ and R1 = 115 kΩ. These values give an

equivalent resistance of Kx = 0.376, a 0.3% error.

Using 1% external resistors and a parallel resistance of 72 k ohms will result in a +/- 6% tolerance in the

value of VDD Fault. The sources of variation due to integrated circuit process variations and mismatches

include the internal reference voltage (less than +/- 1%), the internal comparator hysteresis and offset

(less than +/- 1.7% for part-to-part, processing and environment), the internal resistor value mismatch and

value variations (less than 1.8%), and the external resistor values (1%).

If the 2.3 V default threshold is acceptable, this pin must be left unconnected.

Rev. 1.5

9

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