Rainbow Electronics DS8024 - Manual (Page 7)

DS8024
Smart Card Interface
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Detailed Description
The DS8024 is an analog front-end for communicating
with 3V and 5V smart cards. Using an integrated
charge pump, the DS8024 can operate from a single
input voltage. The device translates all communication
lines to the correct voltage level and provides power for
smart card operation. It can operate from a wide input
voltage range (3.3V to 6.0V). The DS8024 is compatible
with the NXP TDA8024 and is provided in the same
packages. (Note that the PORADJ pin is not present in
the DS8024. Most applications do not make use of this
input pin, instead using the DS8024’s default reset
threshold.)
Power Supply
The DS8024 can operate from a single supply or a dual
supply. The supply pins for the device are V
DD , GND,
V DDA , and PGND. V DD should be in the range of 2.7V
to 6.0V, and is the supply for signals that interface with
the host controller. It should, therefore, be the same
supply as used by the host controller. All smart card
contacts remain inactive during power on or power off.
The internal circuits are kept in the reset state until V
DD
reaches V TH2 + V HYS2 and for the duration of the inter-
nal power-on reset pulse, t W . A deactivation sequence
is executed when V
DD
falls below V
TH2
.
An internal charge pump and regulator generate the
3V or 5V card supply voltage (V
CC ). The charge pump
and regulator are supplied by V
DDA
and PGND. V
DDA
should be connected to a minimum 3.3V (maximum
6.0V) supply and should be at a potential that is equal
to or higher than V
DD .
The charge pump operates in a 1x (voltage follower) or
2x (voltage doubler) mode depending on the input
V
DDA and the selected card voltage (5V or 3V).
• For 5V cards, the DS8024 operates in a 1x mode
for V
DDA
> 5.8V and in a 2x mode for V
DDA
< 5.8V.
• For 3V cards, the DS8024 operates in a 1x mode
for V DDA > 4.1V and in a 2x mode for V DDA < 4.0V.
Voltage Supervisor
The voltage supervisor monitors the V DD supply. A
220µs reset pulse (t
W
) is used internally to keep the
device inactive during power on or power off of the V DD
supply. See Figure 2.
TEMPERATURE
MONITOR
CARD VOLTAGE
GENERATOR
AND
CHARGE PUMP
CLOCK
GENERATION
CONTROL
SEQUENCER
POWER-SUPPLY
SUPERVISOR
I/O TRANSCEIVER
V
DD
GND
V DDA
PGND
CP1
CP2
V
UP
V CC
XTAL1
XTAL2
CLKDIV1
CLKDIV2
5V/3V
CMDVCC
RSTIN
CGND
RST
CLK
PRES
PRES
I/O
AUX1
AUX2
OFF
I/OIN
AUX1IN
AUX2IN
DS8024
Figure 1. Functional Diagram
V DD
ALARM
(INTERNAL SIGNAL)
POWER ON
t W t W
POWER OFF
V
TH2
+ V
HYS2
V
TH2
SUPPLY DROPOUT
Figure 2. Voltage Supervisor Behavior