LTC4558
10
4558fa
10kV ESD Protection
All Smart Card pins (CLKA,B, RSTA,B, I/OA,B, V
CCA,B
and
GND) can withstand over 10kV of human body model ESD
in-situ. In order to ensure proper ESD protection, careful
board layout is required. The GND pin should be tied di-
rectly to a ground plane. The V
CCA,B
capacitors should be
located very close to the V
CCA,B
pins and tied immediately
to the ground plane.
Capacitor Selection
A total of four capacitors is required to operate the LTC4558.
An input bypass capacitor is required at V
BATT
and DV
CC
.
Output bypass capacitors are required on each of the
Smart Card V
CC
pins.
There are several types of ceramic capacitors available,
each having considerably different characteristics. For
example, X7R ceramic capacitors have excellent voltage
and temperature stability but relatively low packing density.
Y5V and X5R ceramic capacitors have apparently higher
APPLICATIONS INFORMATION
Figure 2. Additional Components for Improved Compliance Testing
packing density but poor performance over their rated
voltage or temperature ranges. Under certain voltage
and temperature conditions Y5V, X5R and X7R ceramic
capacitors can be compared directly by case size rather
than specifi ed value for a desired minimum capacitance.
The V
CCA,B
outputs should be bypassed to GND with a 1μF
capacitor. A low ESR ceramic capacitor is recommended
on each V
CC
pin to ensure ESD compliance.
V
BATT
and DV
CC
should be bypassed with 0.1μF ceramic
capacitors.
Compliance Testing
Inductance due to long leads on type approval equipment
can cause ringing and overshoot that leads to testing prob-
lems. Small amounts of capacitance and damping resistors
can be included in the application without compromising
the normal electrical performance of the LTC4558 or Smart
Card system. Generally a 100Ω resistor and a 20pF capaci-
tor will accomplish this, as shown in Figure 2.
100Ω
100Ω
100Ω
20pF
20pF
20pF
20pF
1μF
4558 F02
V
CCA,B
CLKA,B
LTC4558
RSTA,B
I/OA,B
SMART
CARD
SOCKET
