Effect of di/dt and If on trr 8/17/2015 Analog Power Confidential Effect of di/dt Analog Power Confidential Conditions • • • • IF = 10A VDS = 12V AMR438N Sense = 20 m Ohm Analog Power Confidential Results di/dt = 5/40 = 0.125A/ns IRR = 4A ta = 40ns Analog Power Confidential Results di/dt = 5/28 = 0.18A/ns IRR = 6A ta = 33ns Analog Power Confidential Results di/dt = 10/46 = 0.22A/ns IRR = 7A ta = 32ns Analog Power Confidential Results di/dt = 10/34 = 0.3A/ns IRR = 8.5A ta = 32ns Analog Power Confidential Results di/dt = 10/24 = 0.4A/ns IRR = 12A ta = 30ns Analog Power Confidential Results di/dt = 10/2 = 0.5A/ns IRR = 13.5A ta = 28ns Analog Power Confidential Results di/dt = 10/15 = 0.66A/ns IRR = 17A ta = 26ns Analog Power Confidential Results di/dt = 15/19 = 0.8A/ns IRR = 19A ta = 23ns Analog Power Confidential Results di/dt = 20/14 = 1.4A/ns IRR = 25A ta = 21ns Analog Power Confidential Results di/dt = 20/12 = 1.66A/ns IRR = 28A ta = 18ns Analog Power Confidential Summary of Results di/dt A/ns irr A ta ns Qrr: 0.5 x irr x ta nC Irr / di/dt 0.125 4 40 80 32 0.18 6 33 99 33.3 0.22 7 32 112 31.8 0.3 8.5 32 136 28.3 0.4 12 30 180 30 0.5 13.5 28 189 27 0.66 17 26 221 25.8 0.8 19 23 218.5 23.8 1.4 25 21 262.5 17.9 1.66 28 18 252 16.9 Analog Power Confidential Conclusion: di/dt • Irr increases nearly linearly with di/dt at di/dt <0.5A/ns • At higher di/dt, Irr / didt decreases – At very high di/dt Irr is much lower than would be expected using classic fixed qrr model • Likewise trr does not decrease as much as expected at high di/dt – Therefore Qrr does increase with di/dt for low di/dt (<~0.66A/ns) – Qrr does not seem to increase significantly with di/dt for dit/dt > 1 ns Analog Power Confidential Effect of If on Irr Analog Power Confidential Results If = 6A, irr = 8A Analog Power Confidential Results If = 8A, irr = 11A Analog Power Confidential Results If = 12A, irr = 12.5A Analog Power Confidential Results If = 14A, irr = 13A Analog Power Confidential Results If = 16A, irr = 14A Analog Power Confidential Overlay Di/dt changed as If is changed, magnifying the effect. Increase in irr due to IF is negligable Analog Power Confidential Conclusion • At typical full load operating currents seen in DC DC converters, the increase in irr with current is fairly small • At lower currents, say < half typical operating current, the irr does reduce as current is reduced Analog Power Confidential