DS8007A Datasheet, PDF(26/41 Page) Maxim Integrated Products – Multiprotocol Dual Smart Card Interface

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DS8007A Datasheet, PDF (26/41 Pages) Maxim Integrated Products – Multiprotocol Dual Smart Card Interface

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Multiprotocol Dual Smart Card Interface

Card Interface Voltage Regulation

and Step-Up Converter Operation

The VDD and VDDA pins supply power to the DS8007A.

Voltage supervisor circuitry detects the input voltage

levels and automatically engages a step-up converter if

necessary to generate the appropriate voltages to the

card interfaces according to the control register set-

tings. The conversion process is transparent to the user

and is usually only noticed by changes in the VUP pin

voltage, which reflects the operation of the internal

charge pump. Table 2 elaborates on the VUP pin.

The VDD and VDDA pins must be decoupled externally,

but extra care must be taken to decouple large current

spikes that can occur on the VDDA pins because of

noise generated by the cards and internal voltage step-

up circuitry.

Voltage Supply Supervision

The voltage supervisor circuitry monitors VDD and

holds the device in reset until VDD is at a satisfactory

level. The DELAY pin is an external indicator of the

state of internal power and can also be driven external-

ly to hold the device in a reset state. An external capac-

itor is usually attached to this pin, defining the time

constant of a power-on delay for the DS8007A. When

VDD is below the voltage threshold VRST, the charging

path that exists between VDD and DELAY is discon-

nected and a strong pulldown is enabled on the DELAY

pin. Once VDD exceeds VRST, the strong pulldown on

the DELAY pin is released and the pullup to VDD is

enabled, allowing the external DELAY capacitor to be

charged.

The RSTOUT alarm pin is released (allowing it to be

pulled up externally) whenever the DELAY pin voltage

is less than VDRST, whether caused by VDD < VRST or

as a result of external hardware pulling the DELAY pin

Table 2. Step-Up Converter Operation

VDDA

< 2.4

2.4â3.5

3.5â5.5

5.5â6.0

2.4â3.5

> 3.5

2.4â6.0

VOLTAGE (V)

SMART CARD

3.0

1.8

VUP

VDDA

5.7

VDDA

4.1

VDDA

low. The minimum duration of the RSTOUT pulse (tW

specification) is defined by the capacitor connected to

the DELAY pin and is typically 1ms per 2nF. The

RSTOUT pin is driven strongly low once the DELAY pin

exceeds the VDRST voltage threshold.

The SUPL bit is set on initial power-up and is reset

again when the RSTOUT alarm pulse occurs. The SUPL

bit may only be cleared by a read of the HSR register.

Figure 8 illustrates the sequencing of the various sig-

nals involved.

Short-circuit and thermal-protection circuitry prevent

damages done by accidentally shorting the VCCx pins

or when the ambient temperature is exceeding the

maximum operating temperature. When the internal

temperature is approximately +150Â°C, the voltage VCCx

and the drivers to the CLKx, RSTx, I/Ox, C4x, and C8x

signals to both card interfaces are turned off. The PTL

bit in the HSR is set and an interrupt is generated.

When a short is detected on the RSTx pin, the device

initiates a normal deactivation sequence. A short on

I/Ox, C4x, and C8x does not cause deactivation.

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