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ST8024CTR Fiches technique(PDF) 10 Page - STMicroelectronics |
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ST8024CTR Fiches technique(HTML) 10 Page - STMicroelectronics |
10 / 23 page ST8024 10/23 Figure 3: Definition of output and input transition times FUNCTIONAL DESCRIPTION Throughout this document it is assumed that the reader is familiar with ISO7816 terminology. POWER SUPPLY The supply pins for the IC are VDD and GND. VDD should be in the range of 2.7 to 6.5 V. All signals interfacing with the system controller are referred to VDD, therefore VDD should also supply the system controller. All card reader contacts remain inactive during power-on or power-off. The internal circuits are maintained in the reset state until VDD reaches Vth2 +Vhys2 and for the duration of the internal Power-on reset pulse, tW (see Fig.4). When VDD falls below Vth2, an automatic deactivation of the contacts is performed. A DC/DC converter is incorporated to generate the 5 or 3 V card supply voltage (VCC). The DC/DC converter should be supplied separately by VDDP and PGND. Due to the possibility of large transient currents, the two 100 nF capacitors of the DC/DC converter should be located as near as possible to the IC and have an ESR less than 100 m Ω. The DC/DC converter functions as a voltage doubler or a voltage follower according to the respective values of VCC and VDDP (both have thresholds with a hysteresis of 100 mV). The DC/DC converter function changes as follows: VCC = 5 V and VDDP > 5.8 V; voltage follower VCC = 5 V and VDDP < 5.7 V; voltage doubler VCC = 3 V and VDDP > 4.1 V; voltage follower VCC = 3 V and VDDP < 4.0 V; voltage doubler. Supply voltages VDD and VDDP may be applied to the IC in any sequence. After powering the device, OFF remains LOW until CMDVCC is set HIGH. During power off, OFF falls LOW when VDD is below the falling threshold voltage. VOLTAGE SUPERVISOR - WITHOUT EXTERNAL DIVIDER ON PIN PORADJ The voltage supervisor surveys the VDD supply. A defined reset pulse of approximately 8ms (tW) is used internally to keep the IC inactive during power-on or power-off of the VDD supply (see Fig.4). As long as VDD is less than Vth2 + Vhys2, the IC remains inactive whatever the levels on the command lines. This state also lasts for the duration of tW after VDD has reached a level higher than Vth2 + Vhys2. When VDD falls below Vth2, a deactivation sequence of the contacts is performed. |
Numéro de pièce similaire - ST8024CTR |
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Description similaire - ST8024CTR |
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