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june 2009 doc id 15429 rev 1 1/39 AN2938 application note power system demonstration ki t based on the pm6686 dual step-down controller with adjustable voltages and adjustable ldo introduction the pm6686 is a dual step-down controller with adjustable output voltages, adjustable ldo and charge pump circuit for notebook power systems, and this demonstration kit represents a typical application circuit. the demonstration kit for system supply allows the testing of all the pm6686 functions and provides two switching sections, with 5 v (out1) and 3.3 v (out2) outputs from 8 v to 28 v input battery voltage. the operating switching frequency of the two sections is 400 khz/300 khz, respec tively. each switching section delivers more than 8 a of output current. an internal linear regulator can provide 5 v @ 100 ma peak current. the charge pump circuit provi des an auxiliary 12 v output voltage. figure 1. pm6686 demonstration kit for system supply www.st.com
contents AN2938 2/39 doc id 15429 rev 1 contents 1 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 demonstration kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5 demonstration kit layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6 i/o interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7 recommended equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8 quick start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 9 jumper settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1 switching sections - working m odes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.2 enable switching section 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.3 enable switching section 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.4 switching sections - frequency selection (ton) . . . . . . . . . . . . . . . . . . . . 16 9.5 linear regulator ldo enable (en_ldo) . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.6 ldo regulation (ldorefin) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.7 external bypass connections for the linear regulator (byp) . . . . . . . . . . . 18 9.8 out1 switching section regulation (fb1) . . . . . . . . . . . . . . . . . . . . . . . . . 18 9.9 current limit of out1 switching section (ilim1) . . . . . . . . . . . . . . . . . . . . 19 9.10 out2 switching section regulation (refin2) . . . . . . . . . . . . . . . . . . . . . . 19 9.11 current limit of out2 switching section (ilim2) . . . . . . . . . . . . . . . . . . . . 20 9.12 connection of ldo output (=5 v) to the pvcc pin (ldo5v_byp) . . . . . 20 9.13 regulation of the charge pump cp (cp sel) . . . . . . . . . . . . . . . . . . . . . 21 9.14 output 1, virtual esr connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 9.15 output 2, virtual esr connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.16 lgate source for charge pump circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 AN2938 contents doc id 15429 rev 1 3/39 9.17 mosfet dual option, high side connection se ction 1 . . . . . . . . . . . . . . . 22 9.18 mosfet dual option, high side connection se ction 2 . . . . . . . . . . . . . . . 23 10 test setup and performance summ ary . . . . . . . . . . . . . . . . . . . . . . . . . 24 10.1 test setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 11 representative waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 11.1 operating modes-skip, na skip, pwm . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 11.1.1 switching sections soft-start and soft-end . . . . . . . . . . . . . . . . . . . . . . . 26 11.1.2 load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11.1.3 fault management: overvoltage and undervoltage . . . . . . . . . . . . . . . . 31 11.2 typical operating characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 11.2.1 out1 and out2 output efficiency vs load current . . . . . . . . . . . . . . . . 33 11.2.2 out1 and out2 switching frequency vs. load current . . . . . . . . . . . . . 34 11.2.3 out1 and out2 output voltage vs. load current . . . . . . . . . . . . . . . . . . 35 11.2.4 power consumption analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 12 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 list of tables AN2938 4/39 doc id 15429 rev 1 list of tables table 1. component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 table 2. demonstration board test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 table 3. jumper s1 skip (connect skip pin to s1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 table 4. jumper s2 en2 (connect the en2 pin to s2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 table 5. jumper s3 en1 (connect en1 pin to s3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 table 6. jumper s4 ton (connect ton pin to s4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 table 7. jumper s5 en_ldo (connect en_ldo pin to s5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 table 8. jumper s6 ldorefin (connect ldorefin pin to s6) . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 table 9. jumper s7 byp (connect ldo_sw pin to s7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 table 10. jumper s8 fb1 (connect fb1 pin to s8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 table 11. jumper s9 ilim1 (connect ilim1 pin to s9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 table 12. jumper s10 refin2 (connect refin2 pin to s10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 table 13. jumper s11 ilim2 (connect ilim2 pin to s11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 table 14. jumper s12 ldo5v byp (connect pvcc pin to s12) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 table 15. jumper s13 cp sel (connect cp_fb pin to s13) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 table 16. jumper s14 vesr1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 table 17. jumper s15 vesr2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 table 18. jumper s16 cp_source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 table 19. jumper s17 dual_gate_1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 table 20. jumper s18 dual_gate_2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 table 21. document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 AN2938 list of figures doc id 15429 rev 1 5/39 list of figures figure 1. pm6686 demonstration kit for system supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. demonstration kit schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 figure 3. pm6686 demonstration board layout - top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 4. pm6686 demonstration board layout - inner layer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 5. pm6686 demonstration board layout - inner layer 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 6. pm6686 demonstration board layout - bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 7. test setup connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 figure 8. smps pulse skip mode, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 figure 9. smps no-audible skip mode, no load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 figure 10. smps pwm mode, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 figure 11. section 1 soft-start waveforms; 8 a constant current load applied . . . . . . . . . . . . . . . . . . . 26 figure 12. section 2 soft-start waveforms; 8 a constant current load applied . . . . . . . . . . . . . . . . . . . 27 figure 13. out1 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 figure 14. out2 soft-end, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 figure 15. tracking soft-start en2 connected to vref2, no loads applied. . . . . . . . . . . . . . . . . . . . . 28 figure 16. tracking soft-end en2 connected to vref2, no loads applied . . . . . . . . . . . . . . . . . . . . . 29 figure 17. out1 = 5 v pwm load transient 2 a/s 0-5 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 figure 18. out2 = 5 v skip load transient 2 a/s 0-5 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 figure 19. out2 = 3.3 v pwm load transient 2 a/s 0-5 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 figure 20. out2 = 3.3v skip load transient 2 a/s 0 - 5 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 figure 21. undervoltage (uvp) protection management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 figure 22. overvoltage protection management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 figure 23. overvoltage protection management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 figure 24. efficiency out1 = 5 v ton = vcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 figure 25. out2 efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 figure 26. switching frequency vs. load _out1 = 5 v ton = vcc . . . . . . . . . . . . . . . . . . . . . . . . . . 34 figure 27. switching frequency vs. load _out2 = 3.3 v ton = vcc . . . . . . . . . . . . . . . . . . . . . . . . . 34 figure 28. load regulation out1 = 5 v ton = vcc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 figure 29. load regulation out2 = 3.3 v ton = vcc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 figure 30. pwm no load input currents vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 figure 31. skip no load input currents vs. voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 figure 32. na skip no load input currents vs. voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 figure 33. input current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 figure 34. input current consumption vs. input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 main features AN2938 6/39 doc id 15429 rev 1 1 main features 5.5 v to 28 v input voltage range dual fixed 1.05 v/3.3 v and 1.5 v/5.0 v outputs or adjustable 0.7 v to 5.5 v (smps1) and 0 v to 2.5 v (smps2), 1.5% accuracy over valley regulation low side mosfets r ds(on) current sensing and programmable current limit constant on-time control selectable switching frequency soft-start (internally fixed at 2.8 ms) and soft-stop selectable pulse skip ping at light loads selectable minimum frequency (33 khz) in pulse skip mode independent power good and en signals latched ovp and uvp charge pump feedback fixed 3.3 v/5.0 v, or adjustable output 0.7 v to 4.5 v, 1.5% (ldo): 200 ma 3.3 v reference voltage 2.0%: 5 ma 2.0 v reference voltage 1.0%: 50 a AN2938 demonstration kit schematic doc id 15429 rev 1 7/39 2 demonstration kit schematic figure 2. demonstration kit schematic 6 % 3 2 * / 5 4 * / 5 4 # u & 2 % & 6 2 % & |