NCN6001_14 Datasheet, PDF (27/33 Pages) ON Semiconductor – Compact Smart Card Interface IC

NCN6001
INPUT SCHMITT TRIGGERS
All the Logic Input pins have built−in Schmitt trigger
circuits to protect the NCN6001 against uncontrolled
operation. The typical dynamic characteristics of the related
pins are depicted in Figure 30.
The output signal is guaranteed to go High when the input
voltage is above 0.70* V_CC, and will go Low when the input
voltage is below 0.30* V_CC.
OUTPUT
V_bat
ON
OFF
INPUT
0.3 V_bat
0.7 V_bat
V_bat
Figure 30. Typical Schmitt Trigger Characteristic
SECURITY FEATURES
In order to protect both the interface and the external smart
card, the NCN6001 provides security features to prevent
catastrophic failures as depicted hereafter.
Pin Current Limitation: In the case of a short circuit to
ground, the current forced by the device is limited to 15 mA
for any pins, except CRD_CLK pin. No feedback is
provided to the external MPU.
DC/DC Operation: The internal circuit continuously
senses the CRD_VCC voltage and, in the case of either over
or under voltage situation, updates the READ_REG register
accordingly and forces INT pin to Low. This register can be
read out by the MPU.
Battery Voltage: Both the over and under voltage are
detected by the NCN6001, the READ_REG register being
updated accordingly. The external MPU can read the register
through the MISO pin to take whatever is appropriate to
cope with the situation.
ESD PROTECTION
The NCN6001 includes silicon devices to protect the pins
against the ESD spikes voltages. To cope with the different
ESD voltages developed across these pins, the built−in
structures have been designed to handle either 2.0 kV, when
related to the microcontroller side, or 8.0 kV when
connected with the external contacts. Practically, the
CRD_RST, CRD_CLK, CRD_IO, CRD_C4, and CRD_C8
pins can sustain 8.0 kV, the maximum short circuit current
being limited to 15 mA. The CRD_VCC pin has the same
ESD protection, but can source up to 65 mA continuously,
the absolute maximum current being internally limited to
150 mA.
PRINTED CIRCUIT BOARD LAYOUT
Since the NCN6001 carries high speed currents together
with high frequency clock, the printed circuit board must be
carefully designed to avoid the risk of uncontrolled
operation of the interface.
A typical single sided PCB layout is provided in Figure 32
highlighting the ground technique. Dual face printed circuit
board may be necessary to solve ringing and cross talk with
the rest of the system.
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