POWER SUPPLY FUNCTIONS

INPUT VOLTAGE

The TDS9092 needs a +6V to +16V power supply although the lower limit can be made 5.4V by making link A, removing the on-board series diode which normally protects it from power supply reversal. The power supply rise time should be 10ms or better.

You can also run the TDS9092 from a +5V supply, by linking VIN and +5VOUT.

The need for a power supply can be avoided by adding a 470�F/16V capacitor to the board. The TDS9092 can then be supplied from just a miniature 6V transformer. See the FAST START GUIDE for details.

TDS9092 CURRENT CONSUMPTION

Typical current needed by the TDS9092 is as follows. The values do not include current taken by any external loads.

POWERING EXTERNAL CIRCUITS

The voltage regulator can supply up to 180mA at +5V. This includes current for the TDS9092 but is sufficient to power many external C-MOS peripherals and displays. The +5V should be taken from the pin +5VOUT . There is also a power dissipation limit which depends on the application's operating temperature. The table shows the current you can draw, including TDS9092 requirements:

LOW BATTERY DETECTION

A facility for the detection of a low battery is provided. This can be important when the TDS9092 is used in portable equipment. The LBO* pin is from an open drain transistor. It is normally high impedance. If the input voltage falls to 5.8V or below the transistor conducts. Fit a warning LED from the LBO* pin via a 330R resistor to VREC. The LED cathode goes towards the LBO* pin. To adjust the operating point of the low voltage indicator add a resistor from LBI* to GND or VREC. LBI* is the centre part of a voltage divider formed by two resistors (10M and 2M7) on the board. The extra resistor will alter the voltage at LBI* by an amount depending on its value. See CIRCUIT DIAGRAM. LBI* is the Low Battery Input and the trigger is normally set to 5.8V by the two resistors.

TOUCH-SWITCH POWER-ON

Portable applications often have a membrane keyboard. A normal on-off switch is inconvenient. You can have a simple push-to-make switch power up the TDS9092; this can be one of the membrane keys. Connect the Shutdown pin SHDN to one side of the switch and the other to ground. The SHDN pin should also go to one of the parallel output bits. Remove the blue link that normally shorts SHDN to ground. Now closing the switch will power up the computer. In the software initialisation make the parallel bit an output and pull it to ground. This will keep the TDS9092 on even after the finger has gone from the switch. To turn off, arrange that some other input sequence makes the parallel bit an input again. An on-board 10M resistor now pulls up the SHDN pin and the portable instrument switches off.

OTHER FUNCTIONS

A switched +5V output SW+5V is on pin c15. For more information see the section LOW POWER OPERATION.

The whole TDS9092 can be electrically shut down by disconnecting pin SHDN from ground.

The +9V and -9V pins can be used to power external amplifiers, etc.