73S8024C datasheet(7/22 Pages) MAXIM

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DS_8024C_023

73S8024C Data Sheet

Rev. 1.3

DC-DC Converter – Card Power Supply

An internal DC-DC converter provides the card power supply. This converter is able to provide either 3 V

or 5 V card voltage from the power supply applied on the VDD pin. The digital ISO-7816-3 sequencer

controls the converter. Card voltage selection is carried out by the digital input 5V/

#V.

The circuit is an inductive step-up converter/regulator. The external components required are 2 filter

capacitors on the power-supply input VDD (next to the LIN pin, 100 nF + 10 µF), an inductor, and an

output filter capacitor on the card power supply VCC. The circuit performs regulation by activating the

step-up operation when VCC is below a set point of 5.0 or 3.0 volts minus a comparator hysteresis voltage

and the input supply VDD is less than the set point for VCC. When VDD is greater than the set point for VCC

(VDD = 3.6 V, VCC =3 V) the circuit operates as a linear regulator.

Depending on the inductor values, the voltage converter can provide current on VCC as high as 100 mA.

The circuit provides over-current protection and limits ICC to 150 mA. When an over-current condition is

sensed, the circuit initiates a deactivation sequence from the control logic and reports back to the host

controller a fault on the interrupt output

OFF.

Choice of the inductor

The nominal inductor value is 10

µH, rated for 400 mA. The inductor is connected between LIN (pin 5 in

the SO package, pin 2 in the QFN package) and the VDD voltage. The inductor value can be optimized to

meet a particular configuration (ICC_MAX). The inductor should be located on the PCB as close as possible

to the LIN pin of the IC.

Choice of the VCC

Depending on the applications, the requirements in terms of both the V

capacitor

Table 1

minimum voltage and the

transient currents that the interface must provide to the card are different.

shows the

recommended capacitors for each VCC

Table 1: Choice of VCC Pin Capacitor

power supply configuration and applicable specification.

Specification Requirement

Application

Specification

Min VCC

Max Transient

Current Charge

Voltage

Allowed During

Transient Current

Capacitor

Type

Capacitor

Value

EMV 4.0

4.6 V

30 nAs

X5R/X7R w/

ESR < 100 m

Ω

3.3

µF

ISO-7816-3

4.5 V

20 nAs

µF

Table 1: Choice of VCC Pin Capacitor

Over-temperature Monitor

A built-in detector monitors die temperature. When an over-temperature condition occurs, a card

deactivation sequence is initiated, and an error or fault condition is reported to the system controller.

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