Philips Semiconductors
Product specification
IC card interface
8
FUNCTIONAL DESCRIPTION
TDA8024
The DC/DC converter function changes as follows:
•
V
CC
= 5 V and V
DDP
> 5.8 V; voltage follower
•
V
CC
= 5 V and V
DDP
< 5.7 V; voltage doubler
•
V
CC
= 3 V and V
DDP
> 4.1 V; voltage follower
•
V
CC
= 3 V and V
DDP
< 4.0 V; voltage doubler.
Supply voltages V
DD
and V
DDP
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 V
DD
is below the
falling threshold voltage.
8.2
8.2.1
Voltage supervisor
W
ITHOUT EXTERNAL DIVIDER ON PIN
PORADJ
(
OR WITH
TDA8024AT)
Throughout this document it is assumed that the reader is
familiar with ISO7816 terminology.
8.1
Power supply
The supply pins for the IC are V
DD
and GND. V
DD
should
be in the range of 2.7 to 6.5 V. All signals interfacing with
the system controller are referred to V
DD
, therefore V
DD
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
V
DD
reaches V
th2
+ V
hys2
and for the duration of the
internal Power-on reset pulse, t
W
DD
falls below V
th2
, an automatic deactivation of the contacts
is performed.
A DC/DC converter is incorporated to generate the
5 or 3 V card supply voltage (V
CC
). The DC/DC converter
should be supplied separately by V
DDP
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 mΩ.
The DC/DC converter functions as a voltage doubler or a
voltage follower according to the respective values of V
CC
and V
DDP
(both have thresholds with a hysteresis of
100 mV).
The voltage supervisor surveys the V
DD
supply. A defined
reset pulse of approximately 8 ms (t
W
) is used internally to
keep the IC inactive during power-on or power-off of the
V
DD
supply (see Fig.5).
As long as V
DD
is less than V
th2
+ V
hys2
, the IC remains
inactive whatever the levels on the command lines. This
state also lasts for the duration of t
W
after V
DD
has reached
a level higher than V
th2
+ V
hys2
.
When V
DD
falls below V
th2
, a deactivation sequence of the
contacts is performed.
handbook, full pagewidth
VDD
Vth2
+
Vhys2
Vth2
ALARM
(internal signal)
tw
power-on
tw
supply dropout
power-off
MDB053
Fig.5 Voltage supervisor.
2004 July 12
8
PHILIPS [ NXP SEMICONDUCTORS ]
