KTH-2651A Minimum Operating Voltage as Load

Hello,

1. Minimum operating voltage in 4^th Quadrant as sink mode(or load mode)

We have same voltage accuracy in source and sink as the attached table(see png). We have 5 voltage ranges 100mV to 40V. In the minimum range 100mV, we have 5uV programing resolution but +/-(0.02% of reading + 500uV offset) for uncertainty which means that we can set or program 5uV but actual value sources with +/- 500uV uncertainty. This is voltage source mode case (CV mode).
The other case is that we can control output voltage level by compliance voltage in the current source mode. In this case, we have 10mV minimum in compliance voltage programing. I would not recommend the second case for accurate voltage sourcing applications.
 

2. Pulse Condition

Min/Max pulse width/rise time are very wide ranges depending on DUT impedance, source range and measure range. In the voltage source mode, we have usually about 300us ~ 1ms for pulse width. Please check out the datasheet for every individual case.
 

3. Output Off mode

If a DUT is an energy storage device like battery or solar cell, the output off mode must be high-Z mode. The default state of the instrument 2651A is 0V like ground. As soon as lead cables touch the DUT, the instrument should start to discharge the DUT. High-Z mode of output off mode prevents discharging issue in the DUT connection.  
 

Attached an example of Min Operating Voltage from Keithley Eload here.

For an electronic load product type like the 2380 series, you are right to be aware of minimum operating voltage when sinking current.

However, a SourceMeter has very different analog architecture and does not have a similar concern.

If asking the SMU to source negative current (sink current into the HI terminal) you will also specify a (maximum) voltage compliance limit.  But the actual voltage that will develop between the HI to LO terminal is a consequence of the I*R drop external to the SMU and not due to internal I*R drops.
You could short HI to LO and have it sink current and it would be perfectly happy with the near to zero volt drop on HI to LO.

When sourcing current, the minimum allowed voltage compliance programmed value is 10mV.  But you'd set it this low only if you wanted to enforce this as a maximum voltage that the DUT should experience when forcing the current by the SMU.
Instead, you would set the voltage compliance to value larger than the expected I*R of the DUT.

May we know how SourceMeter analog architecture is different from Eload?
If I am not mistaken, SourceMeter also use MOSFET to provide source and sink current and sense resistor to sense the current accurately. Of course, SourceMeter use PCB to have component mounted on it. Either PCB, MOSFET or sense resistor will have higher voltage drop across themselves with higher sink/source current.

Can I ask:  what do you need the operating voltage to be?

I've uploaded a block diagram level of the SMU.

For your question about using it as a load, you will operate it as a current source with a voltage compliance limit.
To operate in quadrant 4 as a load, you would have the SMU source negative current.

The V-meter provides input to the voltage compliance limiting.

 

Taking sink current (source negative current) 12A as an example, assuming the sink current internal path resistance as 10mOhm (R1=R2=R3=R3=R4=R5=2mOhm as shown in attachment), the voltage drop across all these internal resistance is 0.12V (12A x 10mOhm), which is the minimum operating voltage for 12A sink current. If my DUT provides a voltage lower than 0.12V (due to long cable) to FORCE HI and FORCE LO ports, 2681A would not be able to sink 12A. The most it can sink is 10A if 0.1V appears on FORCE HI and FORCE LO ports.

Stands to reason that the SMU that is sinking the current needs to be lower potential than the external voltage source that the SMU is loading.

If need be, the SMU will transition to quadrant 3 (negative current and negative voltage) to allow the source current setpoint to be achieved.

See if the attached PDF helps.

What are you proposing to connect the 2651A to?

We connects 2651A to 0.75V voltage rail with 12A maximum output current.
We have several questions:
1. The transition from quadrant-4 to quadrant-3 is seamless when the load current is rising from 0 to 12A?
2. What is the internal resistance or transition point between quadrant-3 and -4?