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Clocks & Timers
Clocks & Timers Forum
Clock solution providing in phase and 90 / 180 degrees out of phase outputs?
I have two (or three) power supplies that I would like to sync to an external clock. This way the power supplies can be run 180 degrees (or 90 degrees) out of phase from each other to reduce ripple current in the power system.
Is there a synchronizer chip that puts out two (or three) clocks that are 180 degree (or 90 degrees) out of phase with each other to take care of this?
The switcher runs at 300KHz but the SYNC pin will take 200KHz – 400KHz. The input logic levels on the SYNC pin are TTL. Commercial temperatures should be okay here.
What is the phase tolerance for 180 degree inversion? 300 kHz has a period of 3.33 us. Is it possible to use a simple inverter? Like SN7414 with a propagation delay max of 22 ns.
- An LVCMOS input clock could drive multiple inputs of the SN7414 at the cost of increased capacitive loading. The outputs could be direct through 1 inverter for a 180 degree shift or through 2 inverters for the 0 degree shift.
LMK04906 (to be released in May 2012) is a lower-cost version of the LMK04806 (released) with fewer outputs and can provide 2 to 12 multi-phase CMOS/TTL outputs at 300 kHz for synchronizing multiple switchers. Any unused outputs / features may be shut-down to reduce power. Note that this device was not designed specifically for this application and may be overkill in terms of performance/power/size, but does provide a lot of flexibility/programmability if this is important for system performance optimization.
LMK04906 Example Use Case for Generating Multiphase SYNC Outputs at 300 kHz
LMK04906 operates over the industrial temp range and uses a Microwire programming interface (subset of SPI). Note that minimum VCO tuning range of this device (2.37 GHz) limits the lowest output frequency to 284 kHz (= 2.37 GHz / VCO_DIV / CLKout_DIV, where VCO_DIV=8 (max) and CLKout_DIV=1045 (max) ).
The LMK should work but might be overkill for a 300KHz quadrature clock. Like Timothy said the 7414 can produce the complementary outputs easily.
Now for the quadrature phases, I would use the standard positive feedback CMOS oscillator which has 1 inverter, and 3 RC phase shifters with a buffer in a loop.
Hartley oscillator for example with 90 phase shifter>
EE since 1975 It's just a simple application of Ohm's Law . .. Former employee of Bristol Aerospace, Interdiscom, Burroughs/Unisys, Iris Systems, C-MAC ....
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