VStack Manual Description

VStack Manual
Firmware Revision 3
Description
The VStack is a complete variable Voltage circuit board solution for advanced personal
vaporizers that has the largest functional Voltage range and greatest battery compatibility of any
electronic vaporizer on the market. With a throttled 5A output current limit across its full operating
Voltage range, it is also one of the most powerful. It was originally designed for use in the “Maxi
VStack”, an enhanced version of the RoughStack, and is now also available as a standalone board for
those who wish to incorporate it in their own vaporizers. Given its unique design heritage, it can be
incorporated in a wide range of vaporizers that were previously only mechanical switch mods.
The VStack's minimalist interface allows devices integrating it to be incredibly compact, yet
feature rich. All functions are controlled through the manipulation of a single button. Voltage settings
are dialed in directly, one digit at a time, using a corresponding number of button taps. This makes it
possible to enter a new Voltage setting without even looking at the device, and permits atypical Voltage
settings without hindering the entry of more common Voltages. Other features are accessed with a
minimum number of button presses, keeping operation unencumbered.
Key Features
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Large Operating Input Voltage Range Of Up To 19V
Output Voltage Adjustable Over The Full Battery Voltage Range In 0.1VRMS Increments
Compatible With Protected Lithium, IMR, LiFePO4, and NiMH Batteries
Battery Voltage Readout
Atomizer Resistance (Ohm) Readout
Lock Mode To Prevent Accidental Triggering
Configurable Light For "Stealth Mode"
Non-Volatile Flash Memory Storage Of All User Settings
12 Second On-State Safety Timeout
Battery Over-Discharge Protection For Up To Three Series Lithium Cells
Output Short Circuit Protection
5ARMS Minimum Throttled Current Limit
Output Low Indication
Typical Standby Current Consumption Of Less Than 0.01uA
98% Typical Power Efficiency
Charger Compatible In 3.7V Lithium-ion Configuration
Compact Form
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VStack Firmware Revision 3 Manual
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Reference Guide
Button Combinations
Tap-Tap-Tap
Tap-Tap-Tap-Tap
Tap-Tap-Tap-Tap-Tap
Tap-Tap-Hold
Tap-Tap-Tap-Hold
Tap-Tap-Tap-Tap-Hold
Battery Voltage readout
Atomizer resistance (Ohm) readout
Lock/unlock
Voltage set mode
Configure Voltage trip, 1-3 lithium Cells
Turn on/off illumination while the output is active
Error Messages
3 Long Flashes
4 Short Flashes
5 Short Flashes
Output short circuit detected
The switch has been held down for longer than 12 seconds
The input Voltage has fallen below the safe operating range
Output Low Indication
1 Very Short Flash
2 Very Short Flashes
Input Voltage is too low for the set output
Output current is limited
Configuration Change Messages
1 Long Flash
Device unlocked or lighting disabled
2 Short Flashes
Lighting enabled
3 Short Flashes
Device locked
Operating Instructions
Basic Operation
When the device is unlocked, and the button is pressed, the attached atomizer will fire. If
lighting is enabled, the light will also illuminate while the output is active.
All configuration functions are controlled with button presses that have the same timing
constraints. A button “tap” is any button press that is released within half a second of having pressed it.
A “hold” is whenever the button is held longer than this. In input combinations, a button release of
greater than half a second will result in a timeout, ending the input combination. For instance, if the
button is tapped 3 times and then released for more than half a second, while the device is unlocked, a
battery Voltage readout will begin. Another button press at this point will be considered to be the
beginning of a new input combination.
Lock Mode
Tapping the button 5 times in succession will put the device in to or out of lock mode. When in
lock mode, the device will not react to any subsequent button presses until another 5 taps of the button
puts it in to unlocked mode. When entering lock mode, the indicator light will flash three times. When
exiting lock mode, the indicator light will output one long pulse.
It is important to note that, as with all the other settings, the lock status of the device is stored in
flash memory. Therefore, even after a battery change, the device will remain locked if it was locked
before.
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VStack Firmware Revision 3 Manual
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Light Configuration
To change the lighting behavior while active, tap the button 4 times and hold it down on a fifth
press. After a moment, the device will blink one long pulse signaling that lighting has been disabled, or
two short pulses indicating that lighting has been enabled.
The lighting fades in/out every four seconds and can be used for timing usage.
Input Voltage Readout
Tapping the button three times will cause the indicator LED to blink out the input battery
Voltage without loading. The Voltage is rounded to the tenth of a Volt for input Voltages greater than
5V and is output as two digits, the ones and tenths of the Voltage. Each digit is indicated with a
number of short pulses, corresponding to the value of the digit, or a single long pulse indicating a zero.
A longer pause than the one used between the pulses of a digit indicates the start of the next digit. If
the input Voltage is below 5V, as is typical for NiMH and single cell lithium batteries, a third digit for
the hundredths of a Volt will also be output. The Voltage readout can be interrupted at any time by
pressing the button.
Output Voltage Configuration
Tapping the button twice and then holding it on a third press will put the device in output
Voltage set mode. The indicator light will light up and stay on while the button is held to signal that the
device has entered this mode, and it will stay on once the button is let go. At this point it is ready for a
Voltage to be entered. If no further button presses are registered within 1.5 seconds of releasing the
button, the device will flash the currently set Voltage, turn off, and no configuration changes will be
made.
The Voltage configuration takes in two digits, the ones and tenths place of a Voltage. A 1-9 is
entered by tapping the button a corresponding number of times, and a zero is entered by pressing and
holding the button. When entering a zero, the indicator light will turn on when the switch has been
held down long enough to register the zero, completing the entry of that digit. When entering a number
other than zero, releasing the switch for more than half a second will complete the entry for that digit.
At the beginning of entering a digit, the indicator light will turn off. After entering the first digit, the
indicator light will turn back on waiting for a second digit entry. Like the first, entry for the second
digit will timeout if no button press is registered within 1.5 seconds.
After entering two digits, or after a timeout occurs before entering either digit, the indicator
light will blink back the set Voltage. This output is done in the same manner as the input Voltage
readout, but always with two digits. If the readout begins after entering a new Voltage, the set Voltage
will be preceded by a zero digit. The readout can be interrupted at any time by pressing the button.
Entering 0.0 Volts will put the device into its maximum output configuration, effectively
making it output the input Voltage when active. This configuration is for users who are more
comfortable with mechanical switch mods and do not desire a regulated output. This will suppress the
low output Voltage indication when current limiting is not in effect.
If a digit is entered beginning with a tap, holding the button for any length of time after that will
still be interpreted as a single increment. E.g. tap-tap-hold-tap will be read in as a 4. This can be used
to stall during the input.
A number greater than 9 can be inputted into the ones place. Entering more than 9 in the tenths
place will increment the ones place accordingly. If the Voltage entered is above the input Voltage, the
device will record the Voltage but will operate like a simple switch unless it is presented with a large
enough input Voltage under load. If 20 is entered for either digit, it'll either go to the next digit or
consider the entry complete, depending on whether it's the Volts or tenths digit, respectively.
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VStack Firmware Revision 3 Manual
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So that short circuit protection is in force for all possible Voltage settings, there is an enforced
minimum output Voltage. This minimum works out to slightly lower than 1/18 of the input Voltage.
Settings below this minimum will not output any Voltage. For example, settings below 0.5V will not
output anything with an input Voltage of 8.4V.
Atomizer Resistance Readout
Tapping the button four times will cause the indicator LED to blink out the atomizer resistance.
The resistance is rounded to two digits when the resistance is above 1 Ohm, and output as the ones and
tenths of an Ohm. If the measured resistance is below 1 Ohm, a third digit for the hundredths of an
Ohm will also be output without the rounding. The digits are read out in the same format as the input
Voltage. 0.0 will be output when the atomizer resistance is greater than the measurement range.
The load is considered to be outside of the measurement range when the peak current through
the load with the input Voltage is below 1.45A. This does not necessarily mean that the load is open or
that it cannot be powered, just that it is out of range for measurement. The measurement range is
highly dependent on the input Voltage under load. Lower input Voltages will have a lower range.
Typically, for a fully charged single cell Li-ion, this limits the measurement to that of 2.6Ohm or less.
Series dual cell Li-ions are typically limited to reading 5.3Ohms or less.
The resistance measurement furthermore requires the battery to maintain a minimum of 3.2V
while the load is being measured. Four long LED pulses will be output if the input Voltage falls below
this while the load is being measured. Given the combined Voltage and current constraints, atomizer
resistance measurements are generally not possible when the input battery is a single RCR123A.
The accuracy of the resistance readout is highly dependent on the temperature of the output
transistor. The most accurate readings are obtained when the device has had a chance to cool down
after use. Using an output Voltage setting of 0.1V will permit resistance readings without heating up
the atomizer or the output transistor.
Safety Timeout
If the button is held down for longer than 12 seconds the output will turn off and the light will
flash quickly 4 times signaling this condition. The output will turn on again if the button is released
and then pressed again. This is to protect the atomizer from reaching damaging temperatures if
accidentally triggered.
Battery Over-Discharge Protection
Multi-cell battery protection is only intended for use with LiMn2O4, aka IMR, batteries. All
other lithium battery chemistries must incorporate their own over-discharge protection when in series
configurations. For effective over-discharge protection, all cells in series configurations must start off
at the same start of charge. Do not select a trip level below the actual number of series lithium cells.
The battery low Voltage trip level is user configurable by tapping the button three times and
then holding it on a fourth press. The light will flash once quickly and then turn back on, indicating
that the device is in the battery trip selection menu, and it will stay on once the button is let go. At this
point it is ready for a new trip level to be entered. If no further button presses are registered within 1.5
seconds of releasing the button, the device will flash the currently set trip level, turn off, and no
configuration changes will be made.
The trip level can be selected for one, two, or three series lithium cells using a corresponding
number of button taps while in this menu. When a new trip level is selected, the LED will output one
long pulse, confirming the new entry, followed by a number of short pulses corresponding to the new
trip level.
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VStack Firmware Revision 3 Manual
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The device will detect the unloaded input Voltage on start up and will use the largest trip level,
up to the configured level, based on that Voltage. This ensures that the trip level can be reconfigured
even when a higher trip level is selected than the number of cells actually present. In such a case, it
may be necessary to remove the atomizer before the new trip level can be selected.
It is acceptable, and recommend, to select a trip level of two even when only a single Li-ion cell
is present. It will not limit operation with a single Li-ion cell in any way. A setting of one is primarily
for NiMH batteries, for using a setting of two with such batteries can cause a premature trip due to it
being within the detection threshold of two cells. A setting of 3 will similarly cause a premature trip
with dual Li-ion cells.
When the input Voltage drops below the set trip level, the output will turn off and the indicator
light will output five short flashes signaling the low Voltage. This message may also be encountered
when too much current is drawn, even from a fully charged battery, as such a scenario can cause the
battery Voltage to drop below the threshold. In this case, a larger resistance atomizer or higher drain
battery should be substituted.
Over-Current Protection
Output short circuit protection will kick in for peak currents greater than 15A. When this
occurs, the output will turn off immediately and this fault condition will be indicated by three long
flashes of the indicator light. This typically means that the atomizer has too small of a resistance and
that it should be replaced. For a non-transient load the reaction time is about 10us. The reaction time
can be up to 100us for a step function load. This reaction time is quick enough to interrupt an output
short when powered from a lithium ion battery.
A peak over current message may also occur when the internal protection circuitry of the
batteries kicks in, or the input Voltage otherwise drops significantly below 2.5V under load.
Over current limiting will kick in when the effective output current exceeds at least 5ARMS. This
condition is indicated by two quick flashes of the indicator light at the beginning of an output
activation. The current limit is reduced as the output transistor heats up, which can result in current
limiting after the beginning of an output activation even when the loading remains constant.
Output Low Indication
When the device is unable to maintain the set output Voltage, the indicator light will quickly
flash on and off at the beginning of the output activation. If the set Voltage is higher than the input
battery Voltage under load, this will be a single flash. This indicates that the output is limited to that of
the input Voltage under load. Such indication will be suppressed when the output is configured to its
maximum setting using a 0.0V entry. If the current is being limited, there will be two flashes at the
beginning of the output activation. Provided that the button is still depressed, the output will still be on
after either indication but the output Voltage will be limited.
Either of these conditions will only be indicated if they are detected at the beginning of the
output activation. It is possible for the output to fall low in the middle of an activation without any
indication. Such a situation can be detected by releasing and quickly pressing the button again.
Charger Mode
Attaching a 4.2V charger to the output port will put the device in charger mode. This is
signaled by the LED turning on dimly. This mode is only intended for use with a single 3.7V
rechargeable lithium battery. Charger mode is exited when the charger is disconnected. USE OF AN
UNREGULATED OR 5V OUTPUT CHARGER WILL RESULT IN BATTERY FAILURE!
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VStack Firmware Revision 3 Manual
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Battery Notes
ONLY USE RECHARGEABLE BATTERIES! ATTEMPTING TO RECHARGE NONRECHARGEABLE BATTERIES, SUCH AS CR123 BATTERIES, CAN RESULT IN FIRE AND
EXPLOSION!
INSTALLING BATTERIES BACKWARDS WILL CAUSE DAMAGE TO THE DEVICE
ELECTRONICS AND CAN POSSIBLY DAMAGE THE BATTERIES AS WELL! ONLY INSTALL
BATTERIES WITH THE POSITIVE (+) END CONTACTING THE CIRCUIT BOARD PAD AT THE
CENTER OF THE BOARD LABELLED '+'! IN STACKED BATTERY CONFIGURATIONS, THE
POSITIVE END (+) OF THE BOTTOM BATTERY MUST CONTACT THE NEGATIVE END (-) OF
THE TOP BATTERY!
MULTI-CELL BATTERY PROTECTION IS ONLY INTENDED FOR USE WITH LiMn2O4,
(aka IMR) BATTERIES! ALL OTHER LITHIUM BATTERY CHEMISTRIES MUST
INCORPORATE THEIR OWN OVER-DISCHARGE PROTECTION WHEN IN SERIES
CONFIGURATIONS! FOR EFFECTIVE OVER-DISCHARGE PROTECTION, ALL CELLS IN
SERIES CONFIGURATIONS MUST START OFF AT THE SAME STATE OF CHARGE! DO NOT
SELECT A TRIP LEVEL BELOW THE ACTUAL NUMBER OF SERIES LITHIUM CELLS! DO
NOT MIX BATTERIES OF DIFFERENT CHEMISTRIES OR MAKES!
DO NOT USE BATTERIES THAT ARE VISIBLY DAMAGED! DO NOT USE BATTERIES
THAT LACK OR HAVE BREAKS IN THEIR OUTER INSULATIVE CASING!
Although the Maxi VStack is resilient to impact damage, batteries typically are not. USE
CAUTION AFTER A DROP OR OTHER IMPACT EVENT! POINT DEVICE AWAY FROM
PERSON WHEN TESTING AFTER AN IMPACT EVENT! If the device fails to function after a hard
fall, the batteries are the most likely cause and should be replaced.
The Maxi VStack can accept either one 18650, a matched pair of 18350 protected rechargeable
lithium cells, a matched pair of 16340/RCR123A protected rechargeable lithium batteries, or a single
4.8V 16650 NiMH pack. LiMn2O4, NMC, LiFePO4, or NiMH are the only recommended battery
chemistries.
Recommended Loading
High pulse currents reduce the battery life, so a higher atomizer resistance will result in longer
run times. In order to maximize the battery run time while keeping the output Voltage regulated as the
battery discharges, select an atomizer resistance that you find most comfortable running at close to 75%
of the charged battery Voltage. A Voltage setting of 75% of the fully charged battery Voltage, or lower,
will generally keep the output regulated for the full run time of the battery.
Table 1 below contains some recommendations based on battery Voltage and desired power
output. This applies to both single and dual coil atomizers, although typically higher power ranges will
be desired with dual coil atomizers. If the desired power level is unknown, select from the 10W row
and start off at 58% of the input battery Voltage for a 6W output.
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6W
8W
10W
12W
14W
16W
18W
20W
25W
30W
40W
4.2V Battery
1.7 Ohm @ 3.2V
1.2 Ohm @ 3.1V
0.90 Ohm @ 3.0V
0.70 Ohm @ 2.9V
0.60 Ohm @ 2.9V
Not Recommended
Not Recommended
Not Recommended
N/A
N/A
N/A
8.4V Battery
6.5 Ohm @ 6.3V
5.0 Ohm @ 6.3V
4.0 Ohm @ 6.3V
3.0 Ohm @ 6.3V
2.8 Ohm @ 6.3V
2.5 Ohm @ 6.3V
2.2Ohm @ 6.3V
2.0Ohm @ 6.3V
1.6Ohm @ 6.3V
1.3Ohm @ 6.2V
Not Recommended
12.6V Battery
14 Ohm @ 9.4V
11 Ohm @ 9.4V
8.8 Ohm @ 9.4V
7.3 Ohm @ 9.4V
6.3 Ohm @ 9.4V
5.5 Ohm @ 9.4V
4.9Ohm @ 9.4V
4.4Ohm @ 9.4V
3.5Ohm @ 9.4V
3.0Ohm @ 9.4V
2.1Ohm @ 9.2V
Table 1 - Recommended Loading
Builders' Notes
For those interested in designing their own devices using the VStack board, here are the
pertinent electrical connections as viewed from the component side:
Figure 1 – Wiring Connections
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Power Connections
The battery's positive connection can be made either to the switch hole, as shown in Figure 1
above, or to the round pad on the opposite side of the board. The battery's negative connection can be
made to the thru hole, as shown in Figure 1 above, or to any point along the conductive annular ring
that parallels the circumference of the board. The battery's negative must go to both the board and the
shell of the output atomizer connector. For the best output accuracy, it is recommended that the
battery's negative connects directly to the atomizer's shell, with a separate lead going from the
atomizer's shell to the board. This way, the board can sense the Voltage at the output. For the same
reason, the lead between the positive output and the atomizer's center conductor should be kept short.
The atomizer's center conductor can be wired to either the thru hole or the rectangular pad labeled
“P1”. Both thru-holes accept a maximum of 24AWG, which is the recommended wire size for the
output connection.
Switch Selection
The layout for the switch is designed to accept the C&K push button switch, MadVapes SKU#
2429, directly. The switch current is less than 5mA, so many other normally open momentary switches
will also work, with a couple considerations. The full input battery Voltage will be seen across the
switch terminals when off, so the switch should be rated to handle that Voltage. Common 6mm tactile
switches have a Voltage rating of 12V and are not recommended at Voltages higher than that. Switch
noise is also a concern. The common horn switch, for instance, has been found to have an activation
that is highly irregular and can cause false button presses to register. The slots for the switch are placed
0.200” apart, center to center, so any switch that is to be connected directly to the board must have a
similar lead spacing. The tactile switches with spherical actuators, MadVapes SKU#s 10117, 10241
and 11323, are superb choices as they are rated 32V, are quiet, and have a lead pitch of 0.200”.
LED Modifications
If the LED needs to be relocated, leads for it can be attached to pins 7 and 8 of U1, as seen in
Figure 1. The LED can be removed from the PCB without destroying it by using two soldering irons
and acting quickly.
The LED is powered by a 3.0V source and has a series resistance of roughly 200Ohm. If a
higher Voltage LED is substituted, such as a blue, violet, or white LED, the output from it will be very
dim given the relatively low drive power. Increasing the on-board Voltage is strongly advised against
since the multi-cell over-discharge protection, current protection, and resistance readout are all highly
dependent upon that Voltage.
Increasing The Output Current
It is possible to modify the VStack for higher current delivery by adding a second power Pchannel MOSFET in parallel with the one on the board. The connections to do this do not require hot
air work as would be needed to replace the on-board MOSFET. Doing this will break the resistance
readout without further modifications, limit the battery choices to those that can handle the new
maximum output current, and make it easy to end up with a device that is inherently unsafe. MAKE
THIS MODIFICATION AT YOUR OWN RISK!
To do this, the gate of this second MOSFET should be leaded to pin 2 of U1. The source is
most easily connected to the positive switch pin, although this trace really shouldn't carry more than
5A. For more than doubling the maximum current, the second transistor will require its own
connection to the battery's positive terminal. The drain needs two connections, one to the output on the
board and one directly to the atomizer output. The drain wire to the board carries the on-board
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VStack Firmware Revision 3 Manual
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transistor's current contribution and so it must be sized appropriately. It also gives feedback to the onboard circuitry for output Voltage adjustment, current protection, and detecting a charger. The gate lead
doesn't carry much current and can be small, say 28AWG. The other two leads must be sized large
enough to carry the second MOSFET's maximum current contribution.
The on-board transistor has a drain-source resistance of between 39mOhm when cool to
48mOhm when hot. The hot resistance is what the 5A minimum for the current limit is based upon.
This resistance will be in parallel with that of the second transistor, so use it in calculating the new
current limit. The analysis should be made with a gate to source Voltage of 3.0V. In order to more than
double the current delivery, the second MOSFET must have an on resistance that is less than the onboard transistor's at 3.0V. Multiple MOSFETs can be parallelized for the same effect.
One potential choice for a second transistor is an FDD6637, which is in an easy to solder TO252 package. It should increase the current limit to 11-14A for step down Voltages of 2:1 or less. The
limit will be reduced at larger step down Voltages due to saturation. The drain of this MOSFET will
require heat sinking in order to maintain such limits. Due to its turn on characteristics at this Voltage
level, it will not contribute much current if the input battery Voltage drops below 3.2V during use.
This modification, by itself, will disrupt the Ohm readout functionality. It is possible to
preserve that feature by inserting a switch in the second transistor's gate path. A gate-source resistor on
the second transistor will be necessary in this case so that the transistor will turn-off when its gate is
open. 100kOhm will do. When this switch is open, resistance measurements can be made normally.
Specifications
Absolute Maximum Input Voltage: 20V
Current Limit: 5.5ARMS +-0.5ARMS, when VIn > 3.2V under load, Ipeak < 15A, and Tambient = 70°F
Flash Endurance (minimum number of writes before a failure)
Lock Function:
12,000,000
Voltage/Trip Level/Light: 800,000
Changing the light status is half a write by this metric.
Entering the same Voltage or trip level that is already in flash will not result in an additional write.
Input Voltage Readout Accuracy: +-2% at Tambient = 70°F
LED Color: 590nm (Yellow)
Maximum Output Duty Cycle: 100.0%
Minimum Non-Zero Output Voltage: 0.05413 * VIn
Output Voltage Accuracy: +-2%, output duty cycle between 30% and 90%, at Tambient = 70°F
Operating Input Voltage Range: 3.2V – 19V
Peak Over-Current Trip: 15-18A, when VIn > 3.2V under load, at Tambient = 70°F
10us reaction time for a non-transient load
<100us reaction time for a step function load
PCB Assembly Maximum Thickness: 0.130”
PCB Outer Diameter: 0.800”
PWM Frequency: 244Hz
Quiescent Current: 3.5 - 7.5mA, 3.2V < VIn < 20V, LED off
Resistance Readout Accuracy: +-10% when 1.5A < Itest < 15A and Tambient = 70°F, +-20% full range
Standby Current Consumption:
1.5 – 7.8nA, when 3.2V < VIn < 17V, at 70°F
0.22uA Maximum at VIn = 20.0V, 70°F
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Major Firmware Revision Changes
Rev 3
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Added Atomizer Resistance Measurement
Added Configurable Multi-Cell Voltage Trip
Added Over-Current Throttling
Added Low Voltage Readout Hundredths Output
Increased RMS Current Limit From 5.0A To 5.5A
Removed Average Voltage Mode
Removed Reentrant Diagnostics
Rev 2
 Added RMS Voltage Mode
 Increased Switch Timeout From 8s to 12s
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VStack Firmware Revision 3 Manual
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