Technical Note

11/15

BD8918F,BD8918FV,BD8919F,BD8919FV

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2010.4 - Rev.D

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6) Card clock supply

Card clock is supplied from the CLK pin dividing the input frequency of XTAL1 pin with the CLKSEL pin setting. The clock

division switching time is within the 8 clocks of the XTAL1 signal.

The input signal to the XTAL1 pin is made by a crystal oscillator (BD8918F/FV:8Hz, BD8919F/FV:16MHz) between the

XTAL1 pin and XTAL2 pin or external pulse signal.

When a crystal oscillator is used, the voltage between XTAL1 and XTAL2 may decrease to become close to “-1V”, which

is not a problem.

When an external pulse signal is applied to the XTAL1 pin (except for signal input by crystal oscillation), the duty of the

XTAL1 pin should be 48% - 52% and the transition time of the XTAL1 pin should be within 5% of the signal cycle to

ensure the duty factor of 45% - 55% at the CLK pin.

7) RSTIN input, RST output

The RSTIN input becomes effective after the CMDVCCB signal input turns to L from H, activation sequence is initiated

and approximately 48

s after I/O TRANS turns ON. The RST output is released in approximately 472sec (max.

481

sec) after the CMDVCCB signal turns from H to L to output a signal based on the RSTIN input.

8) Fault detection

When the following fault state is detected, the circuit enters the wait mode after it generates an internal alarm signal and

is deactivated.

If a card is not present, it remains in the wait mode.

• When the VCC pin becomes less than 1.6V, or is loaded high current (TYP: 140mA)

• When VDDP voltage is less than the threshold voltage (detected by supply voltage detector)

• When a high temperature is detected by the thermal shutdown circuit

• When the card is removed during operation or the card is not present from the beginning (PRES=L)

9) OFFB output

The OFFB output pin indicates the IC is ready to operate. It is pulled up to VDD with a 20k

 resistor.

When the IC is in the ready state, OFFB is High.

After activation, the OFFB outputs OFF state (Lo) when a fault state is detected.

When a card is present and CMDVCCB becomes High, the internal alarm is released and the OFFB output becomes

High.

Fig. 6 OFFB, CMDVCCB, PRES, VCC operation

BD8918F/FV

CLKSEL

f

clk

BD8919F/FV

CLKSEL

f

clk

1

XTAL

f

1

2

XTAL

f

0

2

XTAL

f

0

4

XTAL

f

端子ショート等による停止動作

カード取り外しによる停止動作

t

debounce

t

debounce

PRES

OFFB

VCC

t

CMDVCCB

Shutdown by card removal

Shutdown by short-circuiting of pins