Tuesday, February 27, 2018

Synchronizing the i6A DC-DC Converter Switching Frequencies

When multiple DC to DC converters are used to power sensitive circuitry, input and output noise can cause system issues, particularly when measuring very low signal voltages.  The problem is compounded if the converters’ switching frequencies vary with input voltage or output load. 

Even when the converter’s operating frequency is fixed, there will be a tolerance on the switching frequency timing circuit between the converters and just a few Hertz differences between the converters can cause sub-harmonic beat frequencies.

Filtering the inputs and outputs is one solution, but this can be complex over a wide frequency bandwidth.  If the DC-DC converters had a fixed switching frequency and could be synchronized to together or tied to a master clock, any board and/or system EMI filtering would be simpler.

Although somewhat uncommon, there are some DC-DC converters that have synchronization capability.  When the “full feature” option is specified on TDK-Lambda’s low cost, fixed frequency, i6A series of 250W non-isolated DC-DC converters, multiple units can have their operating frequency synchronized.

There are four ways to connect the modules:

1. Master / Slave, with no phase shift.  One i6A module is the “master” and the other modules will operate at the master’s switching frequency.  All the modules draw input current at the same time.

 


2. Master / Slave, with 180 degree phase shift.  One i6A module is the “master” and other modules will operate at the master’s switching frequency, but directly out of phase.  This can reduce the peak input ripple current from the supply, requiring less input capacitance.  Any module with a jumper between pins 4 and 33 will have the phase shift function activated.
 

3. An external clock is used with no phase shift.  All the i6A modules operate at the same frequency as the external clock (no master / slave). All the modules draw input current at the same time.
 
4. An external clock is used with a 180 degrees phase shift.  All the i6A modules operate at the same frequency as the external clock (no master / slave), but any module with a jumper between pins 4 and 33 will have the phase shift function activated.  This again reduces the peak input ripple current from the supply, requiring less input capacitance.

 

The i6A non-isolated DC-DC converters are a series of step down converters (the input voltage has to be higher than the output) in the industry standard 1/16th brick footprint.  All models feature wide range input voltages, as high as 9 to 53V and have wide range output adjustment from 3.3 – 15V to 3.3 – 40V.  Operating efficiencies can be as high as 98%.

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