ST8034T datasheet(22/39 Pages) STMICROELECTRONICS

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ST8034T, ST8034AT, ST8034P, ST8034C

Functional description

The voltage supervisor monitors the voltage of the VDD, VDDP and VDD(INTF) supplies and

provides both power-on reset (POR) and supply dropout detection during a card session.

The supervisor threshold voltages for VDD, VDDP and VDD(INTF) are set internally. As long as

VDD, VDDP or VDD(INTF) is less than the corresponding VTH + VHYS, the ST8034 device

remains inactive irrespective of the command line levels. After VDD, VDDP, and VDD(INTF)

have reached a level higher than the corresponding VTH + VHYS, the device still remains

inactive for the duration of tW, a defined reset pulse of approximately 8 ms

(tW = 1024 x 1/fOSC(INT)LOW) when the output of the supervisor keeps the control logic in

reset state. This is used to maintain the device in shutdown mode during the supply voltage

power-on, see Figure 10. A deactivation sequence is performed when either VDD, VDDP or

VDD(INTF) falls below the corresponding VTH.

6.2.2

Voltage supervisor with PORADJ function (ST8034P and ST8034C)

In the case of devices with the PORADJ pin (ST8034P, ST8034C), additional flexibility of the

voltage monitoring is available: the PORADJ pin provides an independent voltage

monitoring input that can be used for VDD(INTF) monitoring (as shown in Figure 9) or

generally for the monitoring of any external voltage to which the resistor divider is

connected, with adjustable threshold.

Undervoltage (UVLO) threshold adjustment on the PORADJ input with the resistor divider:

VDD(INTF) UVLO threshold (falling) = (R1+R2)/R2 x VTH(PORADJ)

VDD(INTF) UVLO threshold (rising) = (R1+R2)/R2 x (VTH(PORADJ) + VHYST(PORADJ))

If the external resistor divider is not used, connect the PORADJ pin to VDD(INTF), then

VDD(INTF) UVLO threshold = VTH(PORADJ).

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