max Vout in fusion digital power designer

The output voltage is controlled by two commands, VOUT_COMMAND and VOUT_MODE.

For the UCD9211, VOUT_MODE is set to 0x14 and cannot be changed, which indicates that the device is using the LINEAR16 format and the exponent used with the linear format is -12.

Output Voltage = VOUT_COMMAND * 2^-12.

The VOUT_COMMAND register is 16 bits so the maximum value that can be represented is 65536.

Maximum Voltage = 65536 * 2^-12 = 16V.

Below is an option you could employ which would fool the controller into believing it is regulating to a voltage within this limitation, such as , if you wanted a 24V output but the controller believes it is running as if the output voltage is 2.4V.  Accordingly, any PMBus reporting of any Output Voltage related commands would have to follow this scaling.

In this case, the voltage feedback resistors would be set to attenuate the output by 1/10 and would result in a 2.4V level at the controller's sense pins (sense pin maximum is 2.5V) when the output is 24V.  Normally, the attenuation of this resistor divider would be entered into the PMBus commands VOUT_SCALE_LOOP and VOUT_SCALE _MONITOR to inform the controller so that the actual voltage reported is correct but for this workaround you would enter a value of 1.000 for these commands.  This will fool the controller into believing it is directly regulating a 2.4V output but the rail will operate at 24V.

Obviously, the host communicating with the controller will need to understand that the voltage reporting will be 1/10 the actual value, but it gives you a method to get around the 16V limitation on VOUT_COMMAND.

Thanks Brad, thats what I thought could be done. My question is more about the tool. If you specify a voltage higher than 16V, will the tool scale the system so that it will operate with the parts bounds? It seems to be able to auto-calculate resistor dividers, etc. but will not accept a Vout value greater than 16V. Is this a tool limitation or am I doing it wrong? Or more appropriately, how can I get the tool to do it?
thx, Nick

The Fusion GUI does not allow a value to be entered which cannot be resolved by the controller.

The maximum controller output voltage is limited to 16V based on the previous calculation, using the definitions for VOUT_COMMAND and VOUT_MODE.

OK, thanks, any way to put in a feature request?