POWER SUPPLY FUNCTIONS

INPUT VOLTAGE

The TDS2020F needs a +6V to +16V power supply although the lower limit can be made 5.4V by making link A. This shorts the on-board series diode that normally protects it from power supply reversal.

It will also run from a +5V supply. Link VIN to +5VOUT and also cut the link H (available from PCB revision C) to exclude the error signal function. With it connected even small dips in the +5V supply might cause a system reset. When running from a +5V supply the voltage should rise quickly, switched mode power supplies can rise slowly and give an improper reset.

CURRENT CONSUMPTION

The two columns show the typical current when executing from external program memory. Add the current taken by any external loads.

POWERING EXTERNAL CIRCUITS

The voltage regulator can supply up to 100mA at +5V. This includes current for the TDS2020F 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 that depends on the application's operating temperature. The table shows the current you can draw, including TDS2020F requirements:

OTHER POWER SUPPLY FUNCTIONS

q       A switched +5V output SW+5V is on pin c15. For more information see LOW POWER OPERATION, page 89.

q       The whole TDS2020F can be electrically shut down by a signal on the pin SHDN. This has an internal 100k resistance to ground and a voltage of anything from +2.0 to +30V will turn off the board.

q       An error signal from the voltage regulator holds the H8/532 microprocessor in reset when the input voltage is below (typically) 5.8V. Because of this the power supply can rise and fall slowly without causing any problem.

q       +8V & -8V on pins z16 & z17 can be used to power external amplifiers etc. They are mainly for the RS232 serial ports and current drain should be limited to a few hundred microamps.