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| TDA8025 Datasheet, PDF (8/38 Pages) NXP Semiconductors – IC card interface | |||
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NXP Semiconductors
TDA8025
IC card interface
After powering up the device, pin OFFN remains LOW until pins CMDVCCN and PRES
are both HIGH or pin CMDVCCN is HIGH and pin PRESN is LOW. During power off, pin
OFFN is driven LOW when VDD(INTREGD) is below the falling threshold voltage (Vth).
When pin CMDVCCN is HIGH, the internal oscillator frequency (fosc(int)) is switched to Low
frequency (inactive) mode to reduce power consumption.
8.2 Voltage supervisors
8.2.1 Block diagram
VDD(INTF)
R1 PORADJ
R2
VDD(INTREGD)
VDD(INTREGD)
REFERENCE
VOLTAGE
Fig 4. Voltage supervisor circuit
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8.2.2 Description
The voltage supervisors provide both the Power-On Reset (POR) and supply drop-out
detection functions. They control the internal regulated supply voltage (VDD(INTREGD)) and
the microcontroller interface supply voltage (VDD(INTF)) to ensure problem-free operation of
the TDA8025.
By monitoring both VDD(INTREGD) and VDD(INTF), the voltage supervisors ensure these
voltages are high enough to ensure correct operation of the TDA8025 and ï¬awless
communication between it and the microcontroller. This information is combined and sent
to the digital controller in order to reset the TDA8025.
An extension of the power-on reset pulse width of ± 8 ms (tw(POR)) is used to maintain the
TDA8025 in inactive mode after the supply voltage power on or off sequences (see
Figure 5).
TDA8025_1
Product data sheet
Vth + Vhys
Vth
VDD(INTREGD)
ALARMN
(internal signal)
tw(POR)
Power on
tw(POR)
Supply dropout
Fig 5. Voltage supervisors VDD(INTREGD) and VDD(INTF)
Rev. 01 â 6 April 2009
Power off
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© NXP B.V. 2009. All rights reserved.
8 of 38
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