TDA8024AT datasheet(9/29 Pages) PHILIPS

9 / 29 page

2004 July 12

Philips Semiconductors

Product speciﬁcation

IC card interface

TDA8024

8.2.2

WITH AN EXTERNAL DIVIDER ON PIN PORADJ (NOT

FOR THE

TDA8024AT)

If an external resistor bridge is connected to pin PORADJ

(R1 and R2 in Fig.1), then the following occurs:

• The internal threshold voltage Vth2 is overridden by the

external voltage and by the hysteresis, therefore:

where Vbridge = 1.25 V typ. and Vhys(ext) = 60 mV typ.

• The reset pulse width tW is doubled to approximately

16 ms.

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 bridge by the IC during power-on,

the input current on pin PORADJ does not cause

inaccuracy of the bridge voltage.

The minimum threshold voltage should be higher than 2 V.

The maximum threshold voltage may be up to VDD.

8.2.3

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.

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

with S1 and S2

the actual values of nominal resistors R1 and R2.

This can be shown as

0.99

× R1 < S1 < 1.01 × R1 and

0.99

× R2 < S2 < 1.01 × R2

Transposed, this becomes

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

and deactivation is always possible for

That is V1 = 1.31 V and V2 = 1.19 V

and

Suppose R1 + R2 = 100 k

Ω, then

= 42.3 k

Ω and R1 = 57.7 kΩ.

Deactivation will be effective at

× (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 Fig.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:

Therefore

= 40.14 k

Ω and R1 = 59.86 kΩ.

Deactivation will be effective at

× (1 + 1.002 × 1.491) = 2.967 V in any case.

If the microcontroller continues to function down to 2.97 V,

the slew rate on VDD should be less than 0.20 V/ms to

ensure that clock CLK is correctly delivered to the card

until time t12 (see Fig.9).

th2(ext)(rise)

-------





bridge

hys(ext)

--------------------





th2(ext)(fall)

-------





bridge

hys(ext)

--------------------

–





---------------------

0.98

-------





0.99

1.01

-----------



 R1

--------

---

1.01

0.99

-----------



 R1

-------

1.02

-------





-------

3.135

1.31

---------------

–



 0.98

1.365

100 k

Ω

2.365

-------------------

-------

3.267

1.310

---------------

–



 0.998

1.491

100 k

Ω

2.49

-------------------

TDA8024AT 数据表(PDF) 9 Page - NXP Semiconductors

TDA8024AT 数据表(HTML) 9 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

数据表下载

链接网址

TDA8024AT 数据表(PDF) 9 Page - NXP Semiconductors

TDA8024AT 数据表(HTML) 9 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

数据表 下载

链接网址

数据表下载