9

LTC4557

4557f

APPLICATIO S I FOR ATIO

10kV ESD Protection

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 pad should be tied

to the ground plane.

Capacitor Selection

A total of four capacitors are required for proper bypassing

of the LTC4557. An input bypass capacitor is required at

low equivalent series resistance (ESR), only multilayer

ceramic chip capacitors should be used to ensure proper

stability and ESD protection.

There are several types of ceramic capacitors available

each having considerably different characteristics. For

example, X7R/X5R ceramic capacitors have excellent volt-

age and temperature stability but relatively low packing

density. Y5V ceramic capacitors have apparently higher

packing density but poor performance over their rated

voltage or temperature ranges. Under certain voltage and

temperature conditions Y5V and X7R/X5R ceramic

capacitors can be compared directly by case size rather

than specified value for a desired minimum capacitance.

capacitor. Capacitors should be placed as close to the

LTC4557 as possible for improved ESD tolerance.

The following capacitors are recommended for use with

the LTC4557:

TYPE

VALUE

CASE SIZE

MURATA PART NUMBER

X5R

1

µF

0603

GRM188R60J105KA01

X5R

0.1

µF

0402

GRM155R61A104KA01

Compliance Testing

Inductance due to long leads on type approval equipment

can cause ringing and overshoot that leads to testing

problems. Small amounts of capacitance and damping

resistors can be included in the application without com-

promising the normal electrical performance of the

LTC4557 or smart card system. Generally a 100

Ω resistor

and a 20pF capacitor will accomplish this as shown in

Figure 2.

100

Ω

100

Ω

100

Ω

20pF

20pF

20pF

0.1

µF

1

µF

4557 F02

CLKX

LTC4557

RSTX

I/OX

SMART

CARD

SOCKET

C1

C3

C2

C7

C5

Figure 2. Additional Components for Improved Compliance Testing