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TA8006ASN

TOSHIBA BIPOLAR LINEAR INTEGRATED CIRCUIT SILICON MONOLITHIC

Toshiba 

TA8006ASN

Functional Description

The TA8006ASN incorporates a constant-voltage 5V power supply function to feed stable power to the CPU and

a system reset function to ensure stable operation of the CPU, etc. These functions are explained below.

(1) Constant-voltage 5V power supply function

This constant-voltage function has the reference voltage Vref in the IC that is insusceptible to temperature

changes and input voltage fluctuations. The power supply circuit is designed in such a way that this

voltage is stepped up to 5V by using an OP amp and a voltage-dividing resistor. These OP amp and

dividing resistor and an output transistor connected to the OP amp output together configure a closed loop.

An overcurrent protection function is incorporated as a protective measure in case a fault such as shorting

to GND occurs in the 5V output. A current detecting resistor is inserted between the BIAS and the IS pins,

and a voltage drop across this resistor is detected by a comparator, thereby suppressing the operation of

the OP amp to ensure that the voltage drop will not exceed 0.3V. In this way, a current limiter function is

actuated to prevent no more current from flowing.

If you are using only the reset timer and not the constant-voltage 5V power supply function, connect the

BIAS, IS, OUT, and COMP pins to GND.

(2) System reset function (See Timing Chart)

• Voltage monitoring function (1)

When powered on, the power-on reset timer starts counting the moment the voltage VCC applied to

the CPU exceeds 4.4V. When powered off, this voltage monitoring function outputs a reset signal

immediately when VCC drops below 4.4V. A reset signal also is output immediately when VCC drops

for some reason during normal operation. Then, when VCC is restored to the normal voltage and

exceeds 4.4V, the power-on reset timer starts counting.

The reset signal is output from the RESET pin and from its inverted output pin, RESET.

• Voltage monitoring function (2)

The WI pin outputs a high when the VCC voltage increases above 4.8V and outputs a low when the

VCC voltage drops below 4.6V. This function only monitors the voltage, operating independently of the

voltage monitoring function (1) and the reset timer function. At power-up, the WI output is inverted

after the application system is released from reset; at power-down, the WI output is inverted before

a reset is output. Therefore, this function can be used for memory write inhibit or similar other

purposes.

• Power-on reset timer function

To allow the 5V constant voltage to stabilize at power-on, as well as provide a sufficient time for the

clock oscillation in the CPU to stabilize, the device remains reset for a predetermined time before

being released from the reset state. The duration of this time can be set as desired by choosing

appropriate values for the external resistor and capacitor connected to the TC pin.

The system starts charging the capacitor when the VCC voltage exceeds 4.4V. When this charge

voltage exceeds 4V, the capacitor is discharged by the IC's internal transistor. When the capacitor is

discharged down to 2V, the reset signal is inverted to deactivate the reset.

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2002-02-27

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