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IWR6843: Could I use lower cost DC2DC to replace PMIC LP87702 on IWR6843ISK reference design?
TLV62569DBVR has PSM (Power saving mode) in which at lower load current DCDC goes into pulse skipping operation which generates lot of lower frequency harmonics which are deleterious for mmWave front end.
In our reference solution we have developed with the PMIC based solution. There are few strong reasons listed below.
1) Higher switching frequency (4MHz) is better as we see less switching harmonics within our IF bandwidth. And easier to filter higher frequency less number of harmonics. 2) Higher switching frequency allows smaller size and lower values of passives components to be used in the design allowing smaller size and lower cost options. 3) Sensor requires 4 supplies hence it’s recommended to have all the power supply synchronized. If 4 different supply has 4 different switching frequency, drifts differently across frequency due to device to device variation and temperature variations then it’s going to cause multiple switching frequency harmonics which are difficult to suppress. 4) Some of the TPS parts switches to very low switching frequency to at lower load current (Mainly to improve the efficiency at lower load current) this causes higher ripple and more switching frequency harmonics that are deleterious for the RF performance. In PMIC we switch at constant frequency using forced PWM mode option. 5) As multiple DCDCs in single chip makes the solution compact and lower BOM count lower PCB area.
