i want to use the LTM4626 buck regulator in my design. the device drives several LDOs and one of the mode of operation is to disable most of the LDOs and keep one LDO running. so in full power the load shall be around 5[A] and in low power mode (only on LDO running) the load shall be around 0.2[A].
also, in the low power mode i must take extra care for power loss. so i would like to keep the regulator with maximum efficiency as possible even in lite loads.
my question is: is it possible to switch from DCM to CCM and in reverse while the device is running without shutting him down?
ive seen that the MODE/CLKIN port must tied to GND when in DCM, so i would like to drive the port with 2:1 mux to toggle from DCM to CCM.
also, i have an eval board for the LTM4626 and would like to do an experiment on the issue, affraid to make demage...
thanks and hope for a quick reply.
The DCM/CCM setting only applies to light load conditions. When the MODE/CLKIN pin is set to DCM, the part will operate in CCM at high loads and DCM at light loads. For your design, simply…
The MODE can be pulled down through a resistor, it just needs to be pulled below the 0.3V Sync Low Threshold from the datasheet. I don't have the numbers on hand to calculate the maximum allowed resistor…
The DCM/CCM setting only applies to light load conditions. When the MODE/CLKIN pin is set to DCM, the part will operate in CCM at high loads and DCM at light loads. For your design, simply connect the MODE/CLKIN pin to GND.
You may also want to look at the LTM4657 which has the same size and pinout as the LTM4626, but is designed for better performance at lower currents (up to 8A).
i checked it in the eval board, i saw what you written. when in DCM and at large load, the device simply worked in CCM (i assumed it because the efficiency was the same as when i tied MODE to vcc).
also, didnt mention that when in high load, i need to work with external synchronization. can i tie the MODE port to GND via a pull down resistor?
if not, then i presume i would need the MUX...
The MODE can be pulled down through a resistor, it just needs to be pulled below the 0.3V Sync Low Threshold from the datasheet. I don't have the numbers on hand to calculate the maximum allowed resistor to set to 0.3V. My estimate is it shouldn't be higher than 10kOhms, but the lower the better.
So in that case, what are the disadvantages of the DCM mode?
why not tiyng the MODE/CLKIN port to GND in every application (i.e. in all other buck regulators on my board)?
While in DCM, output ripple will be higher, EMI will be inconsistent, and when a load is removed, the converter will not be able to pull down on the output voltage, it will be slowly drawn down through the output node's resistance to ground.