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Front end

Turn on transient for passives

• Objectives:
  • We want to observe the transient response of the Front end Passive Block as the voltage is applied to its input and possibly having its own transients. Equipment:
  • Arbitrary function generator.
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Spectrum Analyzer (maybe?). Experiment:
  • We will disconnect the Front end Passive Block from the rest of the SPS and apply a DC load at its output and apply a ramping voltage source at the input simulating the power bus. We will step the voltage in varying times and magnitudes.

Circuit breaker (CB)

CB trip point (make sure fuse doesn't blow)

• Objectives:
  • We want to observe that the fuse (F200) does not blow given an overcurrent condition and the Circuit Breaker Block is in the process of tripping. The design specifies that the fuse should never blow before the circuit-breaker does given all components are operating correctly. Equipment:
  • Arbitrary function generator.
  • Various resistors and potentiometers.
  • Oscilloscope. Experiment:
  • For this experiment we will disconnect the Circuit Breaker Block from the Switcher. We will disconnect the feedback from the +3.3 V SPS output to U251 input pin and directly attach a voltage source to the input pin which we can step to force U251 to turn Q251 on and off which will trigger an overcurrent event as seen by U250. Another experiment is to apply a resistor to the output of U251, namely the node between R252 and R253, and vary that resistance to cause a direct overcurrent event.

Quiescent current draw of U250

• Objectives:
  • With the whole SPS in a shutdown or standby mode U250 is draws the most quiescent current being between 1 mA and 2 mA. We want to observe the transient response of the Front end Passive Block as the voltage is applied to its input and possibly having its own transients. Equipment:
  • Arbitrary function generator.
  • Various resistors and potentiometers.
  • Oscilloscope. Experiment:
  • We will disconnect the Front end Passive Block from the rest of the SPS and apply a DC load at its output and apply a ramping voltage source at the input simulating the power bus. We will step the voltage in varying times and magnitudes.

Switcher

Minimum discontinuous mode current

• Objectives:
  • Besides inductor saturation and thermal dissipation we want to avoid U200 from entering discontinuous mode. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe. Experiment:
  • We will load the output and sweep its value until the U200 enters saturation mode. We will record the output current at which this happens if it does at all. We will then measure the voltage and current across and through L200a/L200b respectively when there is zero current draw.

Minimum output voltage for the minimum on time of U200

• Objectives:
  • We want to vary V_IN to change the duty cycle and hence the on time of U200 and notice the SPS output voltage behavior. Equipment:
  • Voltage source.
  • Oscilloscope.
  • Current probe. Experiment:
  • The duty cycle (D) of a switching voltage regulator is: D = (V_OUT + V_D) / (V_IN - V_SW + V_D), where V_OUT is the SPS output voltage, V_IN is the power bus voltage, V_SW is the voltage drop across the 0.22 ohm switch resistance in U200 and V_D is the voltage drop of CR200. The ON time (t_ON) of the regulator is t_ON = D * f, where f is the 1.5 MHz switching frequency of U200.

Frequency compensation testing & component selection

• Objectives:
  • The frequency compensation will help regulate the SPS output voltage by limiting the bandwidth of the error amplifier and hence the switching frequency of the internal switch in U200. We can help control the amount of ringing at the output. Equipment:
  • Various resistors/potentiometer.
  • Some NMOSFETs.
  • Various active components: oscillator, etc.
  • Arbitrary function generator.
  • Oscilloscope. Experiment:
  • What we will do is apply a switching DC load at the SPS output and sweep its value. The test circuit would be something like applying a square wave signal (we could use an arbitrary function generator or an oscillator, .i.e 555 timer) to the gate of a NMOSFET (with a series resistor), and the drain of the FET connects to the SPS output through a series resistor. There would also be a variable impedance in shunt with the FET, which is comprised of a potentiometer with its two fixed terminals are connected to a voltage rail (5 V or something) and its variable terminal is connected to the gate of another NMOSFET. This will act as a variable impedance in shunt with a fixed load that is either saturated or cutoff. This will introduce load changes in steps and we will then measure the voltage transients at the SPS output. We will first pick values for C206 and R206 and sweep the load while observing the output. Typical starting values for C206 and R206 are 1 nF and 0 ohms respectively and we decrement and increment those values respectively. When we find that the ringing at the output is good enough (i.e. a critically damped response at the output due to a step change in the load) whatever values C206 and R206 end up with will be used. NOTE: Let us call this experiment A.

Light/Heavy load

• Objectives:
  • We will basically preform experiment A but the load changes will be more drastic being almost no load to a heavy load. Equipment:
  • See experiment A. Experiment:
  • See experiment A.

Hot/Cold temperature

• Objectives:
  • We will basically preform experiment A but we will also sweep the temperature. This makes sense as the rocket will experience not an extreme but a noticeable temperature gradient while it is on the ground, during launch and flight. Equipment:
  • See experiment A.
  • Hot plate or hot air gun.
  • Freeze aerosol can. Experiment:
  • See experiment A.

High/Low input voltage

• Objectives:
  • We will basically preform experiment A but we will disconnect the U200's input from the SPS and use a voltage source to sweep the input voltage. The power bus voltage rail is specified to never be below 9 V or more than 20 V under normal operating conditions. This affects U200's efficiency as Vin is changing. Equipment:
  • See experiment A.
  • Voltage supply. Experiment:
  • See experiment A.

Overvoltage (OV)

Start up of OV (no latch-up, no oscillations)

• Objectives:
  • Upon initial power up (meaning all caps and inductors have zero stored energy) we want to make sure that as U200's +3.3 V SPS output rail is being brought up, U251 does not react to any overvoltage glitches at the output which will cause U250 to break the circuit. This could be a problem in that the SPS may take a long time to stabilize because U251 continually responds to overvoltages at the output. Equipment:
  • Oscilloscope.
  • Current probe.
  • Spectrum Analyzer (maybe?) Experiment:
  • This is simply powering up the SPS and observing the output and U251's behavior.

Check adequacy of comparator power supply

• Objectives:
  • Since U251's power is derived from the +3.3 V SPS output which it also simultaneously monitors for overvoltages. C250 is designed to keep power to U251 for 0.5 s given that the SPS output rail falls or other faults happen, it should always keep U251 powered, however the initial power up transients are important to observe. Equipment:
  • Oscilloscope.
  • Current probe.
  • Spectrum Analyzer (maybe?) Experiment:
  • This is simply powering up the SPS and observing the output and U251's behavior.

Secondary supply

Estimation of secondary supply voltage and maximum current

• Objectives:
  • The voltage regulation for this block will most likely be done by a low-dropout (LDO) linear voltage regulator. It was estimated that the node between L200a and L200b will switch between 1.6 V and 7.2 V but the actual value will be determined in experiment. The voltage at the output of the secondary buck should be enough to be regulated down to 5V. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe.
  • Spectrum Analyzer (maybe?) Experiment:
  • With the whole SPS running we will leave the secondary buck voltage regulator unloaded and measure the voltages at the nodes mentioned earlier. When these nominal voltages are noted we will apply a varying load at the output and measure the voltages again. This will give us an idea about how much current we can draw before the loading effect is too much. These values will help specify a LDO.

Cross regulation of dual voltage supplies (what effects do each have on the other)

• Objectives:
  • Along with the mutual coupling of L200a and L200b we want to observe the dependencies between the two +3.3 V and 5 V voltage rails as loads are varied and as the SPS recovers from one of the four fault events. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe.
  • Spectrum Analyzer (maybe?). Experiment:
  • With the whole SPS (including a LDO at the output of the secondary supply) operating nominally we will vary the load at one supply output and view the transients at both outputs. We will then do the same for the other, then we will vary the loads at both supply outputs and view the transients. This will be a trial and error process to extrapolate the dependencies.

Final System block testing

Maximum system current flow

• Due to: Inductor, inductor saturation, temperature, (w and w/o circuit breaker)

• Objectives:

  • There could actually be several "maximum" output currents, meaning the inductor could saturate at a certain output current, U250 could trip at a different current, F200 could blow at another current, etc.. However since there is a hierarchy of protection there will actually only be one effect maximum output current when the whole SPS is running. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe. Experiment:
  • With the whole SPS running nominally, we want to apply a DC load to the output and decrease its value until something happens, i.e. an inductor saturates, U250 trips, the output voltage rail oscillates, etc.. This will be the effective maximum output current.

Temperature rise

• Objectives:
  • We expect that the U200 and the buck inductor will run the hottest. So there will be a temperature gradient across the SPS. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe.
  • Non-contact thermometer (i.e. Infrared thermometer). Experiment:
  • We will apply a varying load (which will not cause any fault events to occur) and notice the temperature gradient across the SPS and each block's and/or component's incremental temperature change.

Cleanliness of OV and CB trip points

• Objectives:
  • When there is an overvoltage and overcurrent trigger event, voltage/current nodes around U250 and U251 will quickly change in value. We want to observe what these transients look like and their effects on other nodes if any. Equipment:
  • Various resistors and potentiometers.
  • Oscilloscope.
  • Current probe.
  • Voltage source.
  • Hot air gun. Experiment:
  • We will disconnect the power bus and apply a voltage source at the SPS input, disconnect the gate of U282 from U280 and connect a voltage source to the gate, vary the load at the SPS output and use a hot air gun which we can use to cause any one of the four trigger events.

Voltage(s) seen when coming out of undervoltage (UV) lockouts (both CB and the switcher)

• Objectives:
  • Only U250 and U200 have UVLO lockout functionality. We want to observe what transients occur when there is an undervoltage event, when the two IC's go into lockout and when the input voltages are brought back up to get the IC's out of lockout, specifically at U250, U200 and the SPS output. Equipment:
  • Oscilloscope.
  • Voltage source.
  • Arbitrary function generator (maybe?). Experiment:
  • We will disconnect the power bus from the SPS and replace it with a voltage source to vary the input voltage to cause the two IC's to enter lockout, stay in lockout for some time and bring them back out of lockout. We may even use an arbitrary function generator to quickly ramp/step the input voltage to see how the IC's will respond.

Efficiency

• Objectives:
  • The specified efficiency of the SPS was to be > 70% at a load current of 400 mA. We will connect a constant source at that load to measure the specified efficiency. Equipment:
  • Oscilloscope.
  • Current probe. Experiment:
  • The efficiency (x) of a switching voltage regulator is: x = P_load / P_total where P_total = V_in * I_INavg = P_load + P_losses where P_load = V_out * I_load and P_losses are the losses internal to U200. We can measure the average input current, I_INavg using a current probe.