Measuring a diode, heating up

This type of diode measurement is less preferred for the final measurement, because the power across the device changes during the transient and the switch-on of the current is slower than the switch-off. However, this is the only practical way to make trial measurements with the booster. Here one can start with a cold device and gradually increasing the power the proper dissipation level and channel range can be found.

• General information
• Hardware setup
• Software setup

General information

In this operation mode the left side of the booster, the Current booster unit will be used (Figure 6-9). This and only this side has to be connected to the Main System Unit.

Figure 6-9: Measurement setup for a diode using the booster equipment

The current can be programmed in the Set Measuring Parameters window as usual, between 1A and 20A. This arrangement can be used only if the forward voltage on the pn junction does not exceed 1.4V at the given current. For devices of higher forward voltage the R-driver booster side can be used.

This setup is typically used when the substrate diode is used for both powering and temperature sensing in an integrated circuit.

If a large VLSI circuit is measured all V_DD and V_SS pins have to be connected in parallel, otherwise the bonding leads can easily be damaged. The programmed current usually does not considerably exceed the maximum I_DD current of the normal operation.

Note: If the booster is connected to the T3Ster Main System Unit, the DVM IN input of the Main System Unit has to be left free.

Hardware setup

• Set the Controlled current source switch of the Main System Unit to ON, set the R-driver switch of the Main System Unit to to PC.
• Connect the I_E+ output of the Main System Unit and the I_E+ input of the current booster unit, using the supplied coaxial BNC cable.
• Connect the R-driver output of the Main System Unit (15 pole Canon) and the R-driver connector of the Current Booster (9 pole Canon) using the control cable.
• Connect the output of a good quality, floating output 5V dc power supply to the U_EXT plugs of the Current booster. Take care of the polarity! The connection has to be realized by thick wires with cross section large enough, in order to avoid undesirable voltage drops.

The LED on the Current booster side which is labeled "External supply connected" will be lighted when the 5V power supply is switched on and the fan will be started.

• Connect the diode under test between the "DUT" terminal screws of the current booster. Take care of the polarity labeled on the booster unit. Ensure good electrical contact.
• Use a shielded two-wire cable with DIN connector to connect the two terminals of the diode to one of the measurement channels of the Main System Unit. In order to diminish the effect of measuring the voltage drop on the powering leads the end of the wires has to be connected to the poles of the diode as close as possible. Suggested polarity: match the ± polarity of the differential input of the measuring channel with the ± signs of the DUT terminals.
  
  

Software setup

• Select the CURRENT BOOSTER item in the Select Configuration window.
• Set the required powering current between +1A ..+20A in the Set Measurement Parameters window. Set the Powering wait/run mode to .

The heating up starts with a cold device at high current. This implies that the compensation voltage of the measurement channel has to be selected accordingly, so that the forward voltage of the diode biased by the high powering current be at the HIGH end of the range when the device is cold.

This compensation procedure is more complex than the one given in Table 6-2 for cooling down. The steps are the following:

• Select the DC radio button in the Single Voltage Measurement window.
• Set the Powering wait/run mode to for a short time and compensate LOW the measurement channel (Compensation - Auto - L button in the Set Measurement Channels window). Set the Powering wait/run mode to again.
• Select the Pulse radio button in the Single Voltage Measurement window
• Use the button in the Set Measurement Channels window to shift the measured value to the right (HIGH) end of the range manually
  

The Digital Voltmeter window can be used to check the actual voltage and current of the device under test.

Note 1: The Controlled current source switch of the Main System Unit is always ON. In such a way the DVM unit always shows a high current, the power is switched by shunting the diode for highest speed.

Note 2: The diode has to be calibrated at the same operating current as used in the heating up measurement. If the thermostat or cold-plate starts from the lowest temperature, the compensation procedure is the same as described above. During the calibration the diode has to be left in the Pulse mode where it was at the end of the compensation, for minimum powering level and minimum temperature difference between the device and the thermostat.

The power calculation is based on the forward voltage at the end of the measurement, i.e. it corresponds to the hot state.