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Test power ICs to withstand radiation

Posted: 21 Dec 2015 ?? ?Print Version ?Bookmark and Share

Keywords:RADAR? satellites? radiation? MOSFET? aerospace?

High-power systems such as RADAR and satellites typically employ integrated power-management ICs. These lightweight devices can replace older modules and provide better power efficiency. But, failure in space is not an option because there is no human around to make repairs. Testing can help assure that the devices will withstand radiation.

In space, electronic components are subject to radiation that can damage MOSFET, BJT, or IGBT on a power-management IC. Radiation failures can cause the entire IC, and thus the entire system, to fail.

There are four major sources of radiation: electrons, protons, heavy ions, and gamma rays. Each radiation source can cause a Single Event Error (SEE). The cause of a SEE is the interaction of the radiation source with the electrons of the silicon electron cloud (figure 1). Radiation can impact an IC is by altering its silicon structure. That must be prevented from becoming a permanent failure or, in the worst case, a disruptive event.

Figure 1: The radiation sources causing the failures SEE. The displacement damages caused by an electron impacting a silicon semiconductor material, having low (a) or high (b) energy. In case (a) the electron snatches one electron during the impact. In case (b) the electron interacts with the electrical field of the nucleus and emits a photon. In case (c) a proton or a heavy ion interacts electrically with the electrons of the silicon electron cloud and creates a hole h+ that is a spot where electrons are missing.

A SEE failure in an integrated component of an IC can be caused by the modification of the threshold voltage of a MOSFET inside a chip. This variation is due to the recombination of holes trapped in the gate oxide and electrons flowing inside the source-drain channel when the transistor is on the ON state (figure 2).

Figure 2: Recombination of holes trapped in the gate oxide and electrons flowing inside the source-drain channel may cause a variation of the threshold voltage and a SEE may occur.

Proper design of testing procedures can minimise SEE failures. On the next page, I'll describe how and automated testing procedure of an IC component used in aerospace applications can account for the effects of the radiation.

Test to eliminate failures
On the previous section, I described the effect of the radiation on the integrated components of an IC inserted in a module for aerospace applications. Let's consider the case of the automated testing of the RDSON of an integrated MOSFET transistor in a DC-DC converter.

The integrated MOSFETS must activate whenever the DC=DC converter drives a load. The turning on is performed by forcing, in the case of the n-channel MOSFET, a positive voltage between the gate and the source terminals and by verifying that the transistor is turned on, having a low voltage between drain and source and carrying an high electric current value. When the MOSFET is on, it behaves like an electrical resistance whose value is RDSON. The code below describes an automatic testing procedure to test the RDSON value of the integrated MOSFET transistor.

pin_force (DVI_VIN, 200e-3, 3.7,RANGE_200_MA,RANGE_5_V,SLOW_VOLTAGE_MODE,TRUE); // VIN=3.7V
pin_force (OVI_SWIRE,30e-3,0,RANGE_30_MA,RANGE_1_V,SLOW_VOLTAGE_MODE,FALSE); // SWIRE=0V
pin_force (DVI_VMID, 50e-3,5.5,RANGE_200_MA,RANGE_5_V,SLOW_VOLTAGE_MODE,FALSE); // VMID=5V
pin_force (DVI_VOUT1,200e-3,5.5,RANGE_200_MA,RANGE_10_V,SLOW_VOLTAGE_MODE,FALSE); // Full Range change => IPOWER > 3V / 120KOHM= 25 uA
pin_force (DVI_VOUT2, 50e-3,-5.5,RANGE_200_MA,RANGE_10_V,FAST_VOLTAGE_MODE,FALSE); // VOUT2=-6V
delay (10);
// SET RESOURCES TO MEASURE VOLTAGE DROP ACROSS THE MOSFET SWITCH WHEN TURNED ON
dvi_13->set_current (DVI_CHANNEL_0, 9.5e-6, RANGE_20_UA); // I_DVI=IR-IREF=(1.2/120.9k)-IREF=10u-500n
dvi_13->set_voltage (DVI_CHANNEL_0, 2, VOLT_2_RANGE);
dvi_13->set_meas_mode (DVI_CHANNEL_0, DVI_MEASURE_VOLTAGE);
delay (1);
pin_force (DVI_LX1, 1e-9,7,RANGE_2_MA,RANGE_10_V,SLOW_VOLTAGE_MODE,TRUE); // LX1=7V (OFF)
pin_force (DVI_LX1,100e-3,0.5,RANGE_200_MA,RANGE_1_V,SLOW_VOLTAGE_MODE,TRUE);//LX1=0.5V (ON)
delay (10);
// Measure RDSON by sequence: 0,0,0,0,0,0,1,0 to EN
bit_seq_rdson (0, 0, 0, 0, 0, 0, 1, 0);
delay (1);
// CLAMP LX1: (0.5V, 100mA) (ON)
V = pin_measure (DVI_LX1, MEASURE_VOLTAGE,RANGE_1_V,AVERAGE,100); // switch voltage drop
I = pin_measure (DVI_LX1, MEASURE_CURRENT,RANGE_1_V,AVERAGE,100); // switch current
delay (1);
// Measure RDSONN1
If (I!=0)
RDSONN1=V/I;

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