Functional description

ST8034HN, ST8034HC

20/31

DocID024511 Rev 2

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

external resistor divider on the PORADJ pin, which provides additional voltage monitoring

flexibility (this pin can be used for monitoring any external voltage, with adjustable

threshold):

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

is used to maintain the device in shutdown mode during the supply voltage power-on, see

Figure 7. Voltage supervisor waveforms

6.3

Clock circuits

The clock signal for the card (CLK output) is either provided by an external clock signal

connected to the XTAL1 pin or generated by a crystal connected between the XTAL1 and

XTAL2 pins. The ST8034 automatically detects if an external clock is connected to XTAL1,

which eliminates the need for a separate clock source selection pin. Automatic clock source

detection is performed on each activation command (falling edge of CMDVCC). The

presence of an external clock on the XTAL1 pin is checked during a time window defined by

the internal oscillator. If the external clock is detected, the crystal oscillator is stopped. If the

clock is not detected, the crystal oscillator is started. When the external clock is used, the

clock signal must be present on the XTAL1 pin before the CMDVCC falling edge. If the

external clock is used, connect it to XTAL1 input and leave the XTAL2 pin floating. The

XTAL1 pin can not be left floating, either a crystal or an external clock source needs to be

connected, or the XTAL1 pin needs to be grounded.