MaxFlex Driver Technical Information

The picture below shows the top view of MaxFlex3. The exposed rectangular gold area just above the (C) TaskLED is a direct thermal interface to the bottom of the switcher IC (on the other side of the PCB). If the power dissipation of the MaxFlex3 board exceeds about 1W it is recommended to affix a heatsink or copper tab to a heatsink to the exposed area. The exposed area is at Ground potential - i.e. electrically connected to the battery GND and LED- pads. This means it is safe to mount the tab to a heatsink that connects to the body of a flashlight, IF the body of the flashlight is the same as the Battery negative or ground.

The two holes below VIN+ (anticlockwise) are both ground pads (input ground and LED- output). MaxFlex3 has LED- common to battery ground input.

The SW hole below LED+ (anticlockwise) is one side of an external momentary action switch. The other side of the switch must be wired to Ground.

Note: it is recommended to keep the maximum wire length between the switch and maxFlex3 less than around 4" (10cm). Having wire leads that are too long can cause the wires to act as an antenna and cause maxFlex3 to respond irregularly or turn on/off by itself.

Note: There are 2 GND connections provided on the PCB, but most installations will require 4 connections to ground (Battery negative/ground, LED-, SW ground and ground for the STAT LED- if used). It is recommended to wire LED- and Battery negative to the same PCB ground hole and wire STAT LED- and SW ground to the other PCB ground point. Both PCB ground points are equivalent.

Note the pin labeled STAT in the bottom/center of the board. Refer to the operating manual above for how STAT can be used to drive a Red or Amber LED to warn of low voltage.

Note, MaxFlex3 is a Boost regulator (step up), so input voltage must be less than the output voltage to ensure MaxFlex3 remains in regulation. If the input voltage exceeds the output voltage (at the dialed in drive current), MaxFlex3 will no longer regulate and the input voltage will go through the series inductor and schottky diode directly to the load. This will cause the output current to a LED to rise rapidly since LEDs have a very steep Current vs Voltage curve (Vf).

Note, Input_current should be around 3A or less for optimal performance of MaxFlex3. When running at high output power it is recommended to solder or use thermal epoxy to mount a tab to the pad on the back of the MaxFlex3 board (the pad is at ground potential) and to thermal epoxy/solder/bolt it to a heatsink or the body of the flashlight.

Input Volts	Input Amps	# of LEDs	Output Volts	Output Amps	Efficiency
5.5	2.25	4	14.4	720mA	84%
6.58	1.82	4	14.4	720mA	87%
7.65	1.54	4	14.4	720mA	88%
9.78	1.18	4	14.4	720mA	90%
11.74	1.66	4	15.3	1190mA	93%
5.89	2.86	4	14.4	975mA	83%
7.07	2.29	4	14.5	982mA	88%
9.52	1.65	4	14.5	990mA	91%
9.41	2.91	6	23.3	1024mA	87%
12.0	2.21	6	23.3	1030mA	90%
14.3	1.84	6	23.2	1038mA	91%

Note: it is not recommended to run maxFlex3 at >3A input current, the above tests were to demonstrate the reduced efficiency at the higher input currents.

To determine the heat being dissipated on the maxFlex3 driver, calculate the output power as in the above equation (Step 1). Use the chart above to approximate the efficiency that the driver will be running at.

Lets assume 4 LEDs running at a nominal 1A from a 9.6V NiMH battery pack. From above we have the following:

As power being dissipated increases beyond 1.5W the thermal path to the heatsink becomes critical to reliable operation. Most of the heat being dissipated in the driver is from the switcher IC, U1. The thermal interface (the gold area) is tied directly to the bottom of U1 using thermal vias. Mounting an adequate heatsink with a non-conductive thermal epoxy is recommended. Use a "thin" smear of non-conductive thermal epoxy (like Arctic Alumina) rather than a thick layer.

Additional heatsinking to the top surface of U1 (the plastic package) can help a little, but not nearly as much as providing a good heatsink to the gold area.

Beyond 2W of dissipation thermal management becomes more challenging and it is highly recommend that the thermal protection be enabled in the menu system. Start with 70°C in the menu and refine as needed.

Areas of the circuitry on MaxFlex3 utilize high impedance paths and if potting (not required) is to be utilized, the user must ensure than the compound is non-conductive and non-capacitive otherwise correct operation may be compromised.

Rather than potting, it is recommended to use the thermal interface pad on maxFlex3 to connect to a heatsink. A thermal epoxy product like Arctic Alumina is recommended since it is non-conductive and non-capacitive.

Soldering is also another option if copper or tinplated material is to be used as the tab. Please ensure that the board is not overheated during the soldering process - if in doubt use thermal epoxy instead.

The picture below shows the top view of MaxFlex2. The exposed rectangular gold area just above the (C) TaskLED is a direct thermal interface to the bottom of the switcher IC (on the other side of the PCB). If the power dissipation of the MaxFlex2 board exceeds about 1W it is recommended to affix a heatsink or copper tab to a heatsink to the exposed area. The exposed area is at Ground potential - i.e. electrically connected to the battery GND and LED- pads. This means it is safe to mount the tab to a heatsink that connects to the body of a flashlight, IF the body of the flashlight is the same as the Battery negative or ground.

The two holes below VIN+ (anticlockwise) are both ground pads (input ground and LED- output). MaxFlex2 has LED- common to battery ground input.

The SW hole below LED+ (anticlockwise) is one side of an external momentary action switch. The other side of the switch must be wired to Ground.

Note: it is recommended to keep the maximum wire length between the switch and maxFlex2 less than around 4" (10cm). Having wire leads that are too long can cause the wires to act as an antenna and cause maxFlex2 to respond irregularly or turn on/off by itself.

Note the pin labeled STAT in the bottom/center of the board. Refer to the operating manual above for how STAT can be used to drive a Red or Amber LED to warn of low voltage.

Note, MaxFlex2 is a Boost regulator (step up), so input voltage must be less than the output voltage to ensure MaxFlex2 remains in regulation. If the input voltage exceeds the output voltage (at the dialed in drive current), MaxFlex2 will no longer regulate and the input voltage will go through the series inductor and schottky diode directly to the load. This will cause the output current to a LED to rise rapidly since LEDs have a very steep Current vs Voltage curve (Vf).

Note, Input_current should be around 3A or less for optimal performance of MaxFlex2. When running at high output power it is recommended to solder or use thermal epoxy to mount a tab to the pad on the back of the MaxFlex2 board (the pad is at ground potential) and to thermal epoxy/solder/bolt it to a heatsink or the body of the flashlight.

Input Volts	Input Amps	# of LEDs	Output Volts	Output Amps	Efficiency
5.5	2.25	4	14.4	720mA	84%
6.58	1.82	4	14.4	720mA	87%
7.65	1.54	4	14.4	720mA	88%
9.78	1.18	4	14.4	720mA	90%
11.74	1.66	4	15.3	1190mA	93%
5.89	2.86	4	14.4	975mA	83%
7.07	2.29	4	14.5	982mA	88%
9.52	1.65	4	14.5	990mA	91%
9.41	2.91	6	23.3	1024mA	87%
12.0	2.21	6	23.3	1030mA	90%
14.3	1.84	6	23.2	1038mA	91%

Note: it is not recommended to run maxFlex2 at >3A input current, the above tests were to demonstrate the reduced efficiency at the higher input currents.

To determine the heat being dissipated on the maxFlex2 driver, calculate the output power as in the above equation (Step 1). Use the chart above to approximate the efficiency that the driver will be running at.

Lets assume 4 LEDs running at a nominal 1A from a 9.6V NiMH battery pack. From above we have the following:

Additional heatsinking to the top surface of U1 (the plastic package) can help a little, but not nearly as much as providing a good heatsink to the gold area.

Areas of the circuitry on MaxFlex2 utilize high impedance paths and if potting (not required) is to be utilized, the user must ensure than the compound is non-conductive and non-capacitive otherwise correct operation may be compromised.

Rather than potting, it is recommended to use the thermal interface pad on maxFlex2 to connect to a heatsink. A thermal epoxy product like Arctic Alumina is recommended since it is non-conductive and non-capacitive.

The following section is historical reference data for the previous maxFlex PCB design.

The picture below shows the top view of MaxFlex. The exposed rectangular tinned area just above the (C) TaskLED is a direct thermal interface to the bottom of the switcher IC (on the other side of the PCB). If the power dissipation of the MaxFlex board exceeds about 1W it is recommended to affix a heatsink or copper tab to a heatsink to the exposed area. The exposed area is at Ground potential - i.e. electrically connected to the battery GND and LED- pads. This means it is safe to mount the tab to a heatsink that connects to the body of a flashlight, IF the body of the flashlight is the same as the Battery negative or ground.

The two holes below VIN+ (anticlockwise) are both ground pads (input ground and LED- output). MaxFlex has LED- common to battery ground input.

The SW hole below LED+ (anticlockwise) is one side of an external momentary action switch. The other side of the switch must be wired to Ground.

Note the pin labeled STAT in the bottom/center of the board. Refer to the operating manual above for how STAT can be used to drive a Red or Amber LED to warn of low voltage.

Note, MaxFlex is a Boost regulator (step up), so input voltage must be less than the output voltage to ensure MaxFlex remains in regulation. If the input voltage exceeds the output voltage (at the dialed in drive current), MaxFlex will no longer regulate and the input voltage will go through the series inductor and schottky diode directly to the load. This will cause the output current to a LED to rise rapidly since LEDs have a very steep Current vs Voltage curve (Vf).

Now, Input_current should be around 2.2A or less for optimal performance of MaxFlex. When running at high output power it is recommended to solder or use thermal epoxy to mount a tab to the pad on the back of the MaxFlex board (the pad is at ground potential) and to thermal epoxy/solder/bolt it to a heatsink or the body of the flashlight.

Input Volts	Input Amps	# of LEDs	Output Volts	Output Amps	Efficiency
5.5	2.25	4	14.4	720mA	84%
6.58	1.82	4	14.4	720mA	87%
7.65	1.54	4	14.4	720mA	88%
9.78	1.18	4	14.4	720mA	90%
11.74	1.66	4	15.3	1190mA	93%
5.89	2.86	4	14.4	975mA	83%
7.07	2.29	4	14.5	982mA	88%
9.52	1.65	4	14.5	990mA	91%
9.41	2.91	6	23.3	1024mA	87%
12.0	2.21	6	23.3	1030mA	90%
14.3	1.84	6	23.2	1038mA	91%

Note: it is not recommended to run maxFlex at >2.6A input current, the above tests were to demonstrate the reduced efficiency at the higher input currents.

To determine the heat being dissipated on the maxFlex driver, calculate the output power as in the above equation (Step 1). Use the chart above to approximate the efficiency that the driver will be running at.

Lets assume 4 LEDs running at a nominal 1A from a 9.6V NiMH battery pack. From above we have the following:

Areas of the circuitry on MaxFlex utilize high impedance paths and if potting (not required) is to be utilized, the user must ensure than the compound is non-conductive and non-capacitive otherwise correct operation may be compromised.

Rather than potting, it is recommended to use the thermal interface pad on maxFlex to connect to a heatsink. A thermal epoxy product like Arctic Alumina is recommended since it is non-conductive and non-capacitive.