TDA8024T/C1 View Datasheet(PDF) - NXP Semiconductors.
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Description
Manufacturer
TDA8024T/C1 Datasheet PDF : 33 Pages
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NXP Semiconductors
TDA8024
Standard smart card interface
8.2.3 Applications 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.
8.2.3.1 Microcontroller requiring a 3.3 V 20 % supply
For a microcontroller supplied by 3.3 V with a 5% regulator and with resistors R1, R2
having a 1% tolerance, the minimum supply voltage is 3.135 V.
VPORADJ = k VDD, where
R1 and R2.
k
=
-------S---1--------
S1 + S2
with S1 and S2 the actual values of nominal resistors
This can be shown as:
0.99 R1 < S1 < 1.01 R1 and
0.99 R2 < S2 < 1.01 R2
Transposed, this becomes
1 + 0.98 RR-----12-
=
1
+
01---..--90---91-
R-----1-
R2
1--
k
1--
k
1
+
10----..-09---19-
R-----1-
R2
=
1
+
1.02
RR-----12-
If V1 = Vth(ext)(rise)(max) and V2 = Vth(ext)(fall)(min) activation will always be possible if VPORADJ
> V1 and deactivation will always be done for VPORADJ < V2.
Activation is always possible for
V
DD
V-----1-
k
and deactivation is always possible for
VDD
V-----2-
k
That is V1 = 1.31 V and V2 = 1.19 V and
R-----1-
R2
3----.-1---3---5-
1.31
–
1
0.98
=
1.365
Suppose R1 + R2 = 100 k, then R2 = -1---0--0-----k------ = 42.3 k and R1 = 57.7 k.
2.365
Deactivation will be effective at V2 (1 + 1.02 1.365) = 2.847 V in any case.
If the microcontroller continues to function down to 2.80 V, the slew rate on VDD should be
less than 2 V/ms to ensure that clock CLK is correctly delivered to the card until time t12
(see Figure 9).
8.2.3.2 Microcontroller requiring a 3.3 V 10% supply
For a microcontroller supplied by a 3.3 V with a 1% regulator and with resistors R1, R2
having a 0.1% tolerance, the minimum supply voltage is 3.267 V.
The same calculations as in Section 8.2.3.1 conclude:
TDA8024
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 4.0 — 3 June 2016
© NXP Semiconductors N.V. 2016. All rights reserved.
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