ST8024LTR STMicroelectronics, ST8024LTR Datasheet - Page 19

• Manufacturer Part Number: ST8024LTR
• Description: Interface - Specialized Smart card interface 3V or 5V 26 MHz
• Manufacturer: STMicroelectronics

Specifications of ST8024LTR

• Product Category: Interface - Specialized
• Rohs: yes
• Product Type: Smart Card Interface
• Operating Supply Voltage: 2.7 V to 6.5 V
• Supply Current: 1.2 mA
• Maximum Power Dissipation: 0.56 W
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: TSSOP-20
• Minimum Operating Temperature: - 25 C

ST8024L
6.2.2
Note:
6.2.3
Figure 4.
With an external divider on pin PORADJ
In this case, a resistor divider is connected to the PORADJ pin (see
and V
voltages on pin PORADJ that switch the device on and off. By knowing these values and
using the formula:
it is possible to set R
thresholds, in order to turn the device on and off (R
In particular, R
microcontroller off, the smartcard must also be switched off properly. The same is true for
the microcontroller startup - in such case the smartcard must be turned on after the
microcontroller. The reset pulse width t
Input PORADJ is biased internally with a pull-down current source of 4 µA which is removed
when the voltage on pin PORADJ exceeds 1 V.
This ensures that after detection of the external divider by the ST8024L during power-on,
the input current on pin PORADJ does not cause inaccuracy of the divider voltage.
The V
of the ST8024 device. If, for example, the microcontroller is shut down at 2.5 V, the
appropriate external resistor values must be chosen to ensure proper deactivation of the
ST8024L device.
Application examples
The voltage supervisor is used as power-on reset and as supply dropout detection during
a card session. Supply dropout detection is to ensure that a proper deactivation sequence is
followed before the voltage is too low. For the internal voltage supervisor to function, the
system microcontroller should operate down to 2.35 V to ensure a proper deactivation
sequence. If this is not possible, external resistor values can be chosen to overcome the
problem.
th(ext) fall
th(ext)
threshold of the ST8024L is slightly lower (by 80 mV typ.) than it was in the case
Voltage supervisor
are the external rising threshold voltage and the external falling threshold
1
and R
V
V
DD
DD
1
and R
2
UVLO threshold (rising) = (R1+R2)/R2 x V
UVLO threshold (falling) = (R1+R2)/R2 x V
must be set so that, when V
2
in order to get suitable values for V
Doc ID 17709 Rev 5
W
is doubled to approximately 16 ms.
1
DD
+ R
is getting low, before turning the
2
= 100 kΩ typ.).
DD
th(ext)rise
th(ext)fall
Functional description
Figure
undervoltage (UVLO)
1). V
th(ext) rise
19/35