AN1978 STMicroelectronics, AN1978 Datasheet - Page 10

• Manufacturer Part Number: AN1978
• Description: ST8004: SMART CARD INTERFACE
• Manufacturer: STMicroelectronics

AN1978 - APPLICATION NOTE
Figure 13: Vth2 threshold.
5.2. Vcc short-circuit protection
An important feature of the voltage regulator is the short-circuit protection that warns the sequencer
block (see Figure 1) if the output current grows more than the short circuit current limit (about 90mA). In
this case a deactivation sequence starts to protect the card and the OFF pin falls down warning the
occurred fault as shown in Figure18. The following figures (Figure 14 and Figure 15) show the load curve
of the ST8004 Step-up converter and regulator.
As specified in the NDS electrical requirements the ST8004 is able to maintain the Vcc voltage included
in the range 4.75V÷5.25V for the Class-A and 2.80V÷3.20V for the Class-B with current load from 0 to
the short-circuit current.
An example of short circuit protection intervention is shown in Figure 16, in which the activation
sequence starts in presence of a Vcc short circuit and the protection acts at the end of the activation
sequence.
If the short circuit condition happens when the device is already activated, the protection acts
immediately as shown in Figure 17.
10/14
Conditions:
Conditions:
V
V
V
V
V
V
5/3V=H.
5/3V=H.
CH1: Vcc
CH1: Vcc
CH2: V
CH2: V
CH3: RST pin.
CH3: RST pin.
When the V
When the V
below
below
(about 2.1V) a deactivation
(about 2.1V) a deactivation
sequence starts; the RST
sequence starts; the RST
pin (CH3) is the first to go
pin (CH3) is the first to go
low after about 6µs.
low after about 6µs.
THSEL
THSEL
DD
DD
DDP
DDP
= 4.5V to 2V;
= 4.5V to 2V;
=5V;
=5V;
= V
= V
DD
DD
the
the
.
.
DD
DD
DD
DD
or floating;
or floating;
Vth2
Vth2
voltage falls
voltage falls
value
value