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july 2010 ? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 FAN7621B ? pfm controller for half-bridge resonant converters FAN7621B pfm controller for half-bridge resonant converters features ? variable frequency control with 50% duty cycle for half-bridge resonant converter topology ? high efficiency through zero voltage switching (zvs) ? fixed dead time (350ns) ? up to 300khz operating frequency ? pulse skipping for frequency limit (programmable) at light-load condition ? remote on/off control using con pin ? protection functions: over-voltage protection (ovp), overload protection (olp), over-current protection (ocp), abnormal over-current protection (aocp), internal thermal shutdown (tsd) applications ? pdp and lcd tvs ? desktop pcs and servers ? adapters ? telecom power supplies ? video game consoles description the FAN7621B is a pulse frequency modulation controller for high-efficiency half-bridge resonant converters. offering everything necessary to build a reliable and robust resonant converter, the FAN7621B simplifies designs and improves productivity, while improving performance. the FAN7621B includes a high- side gate-drive circuit, an accurate current controlled oscillator, frequency limit circuit, soft-start, and built-in protection functions. the high-side gate-drive circuit has a common-mode noise cancellation capability, which guarantees stable operation with excellent noise immunity. using the zero-voltage-switching (zvs) technique dramatically reduces the switching losses and efficiency is significantly improved. the zvs also reduces the switching noise noticeably, which allows a small-sized electromagnetic in terference (emi) filter. the FAN7621B can be applied to various resonant converter topologies; such as series resonant, parallel resonant, and llc resonant converters. related resources an4151 ? half-bridge llc resonant converter design using fsfr-series fairchild power switch (fps tm ) ordering information part number operating junction temperature package packaging method FAN7621Bsj -40 c ~ 130 c 16-lead small outline package (sop) tube FAN7621Bsjx tape & reel
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 2 FAN7621B ? pfm controller for half-bridge resonant converters application circuit diagram r sense FAN7621B c dl v cc lv cc rt con cs sg pg ctr hv cc cr l lk lm ns v o d1 d2 r f c f np ns ka431 v in ho lo figure 1. typical application circuit ( llc resonant half-bridge converter) block diagram olp tsd lv cc good low-side gate drive high-side gate drive 6 1 12 10.0 / 12.5 v v ref internal bias lv cc good 3 ho cs con lv cc hv cc ctr r t v aocp pg lv cc ovp time delay 2 8 16 9 time delay + - v ocp + - + - + - + - -q q r s lv cc <5v latch protection -q q r s auto-restart protection + - 0.4 / 0.6 v 5 v 23 v 0.58 v 0.9 v 8.7 / 9.2 v hv cc good + - i ctc + - + - 3v 1v -q q r s f/f level-shift balancing delay shutdown without delay 50ns delay -1 2i ctc v ref i ctc 350ns 350ns 10 sg delay 1.5s 2v + - coun ter (1/4) lv cc i olp 14 lo figure 2. internal block diagram
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 3 FAN7621B ? pfm controller for half-bridge resonant converters pin configuration (3) ho (4) nc pg (16) FAN7621B nc (13) nc (15) (5) nc (6) con (7) nc lo (14) lv cc (12) cs (9) nc (11) sg (10) (2) ctr (1) hv cc (8) r t figure 3. package diagram pin definitions pin # name description 1 hv cc this is the supply voltage of the high-side gate-drive circuit ic. 2 ctr this is the drain of the low-side mosfet. ty pically, a transformer is connected to this pin. 3 ho this is the high-side gate driving signal. 4 nc no connection. 5 nc no connection. 6 con this pin is for a protection and enabling/disabli ng the controller. when the voltage of this pin is above 0.6v, the ic operation is enabled. when the voltage of this pin drops below 0.4v, gate drive signals for both mosfets are disabl ed. when the voltage of this pin increases above 5v, protection is triggered. 7 nc no connection. 8 r t this pin programs the switching frequency. typically, an opto-coupler is connected to control the switching frequency for the output voltage regulation. 9 cs this pin senses the current flowing through the low-side mosfet. typically, negative voltage is applied on this pin. 10 sg this pin is the control ground. 11 nc no connection. 12 lv cc this pin is the supply voltage of the control ic. 13 nc no connection. 14 lo this is the low-side gate driving signal. 15 nc no connection. 16 pg this pin is the power ground. this pin is connected to the source of the low-side mosfet.
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 4 FAN7621B ? pfm controller for half-bridge resonant converters absolute maximum ratings stresses exceeding the absolute maximum ratings may damage the device. the device may not function or be operable above the recommended operating conditions and stressing t he parts to these levels is not recommended. in addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. the absolute maximum ratings are stress ratings only. t a =25 c unless otherwise specified. symbol parameter min. max. unit v ho high-side gate driving voltage v ctr -0.3 hv cc v v lo low-side gate driving voltage -0.3 lv cc lv cc low-side supply voltage -0.3 25.0 v hv cc to v ctr high-side v cc pin to center voltage -0.3 25.0 v v ctr center voltage -0.3 600.0 v v con control pin input voltage -0.3 lv cc v v cs current sense (cs) pin input voltage -5.0 1.0 v v rt r t pin input voltage -0.3 5.0 v dv ctr /dt allowable center voltage slew rate 50 v/ns p d total power dissipation 16-sop 1.13 w t j maximum junction temperature (1) +150 c recommended operating junction temperature (1) -40 +130 t stg storage temperature range -55 +150 c note: 1. the maximum value of the recommended operating junc tion temperature is limited by thermal shutdown. thermal impedance symbol parameter value unit ja junction-to-ambient thermal impedance 16-sop 110 oc/w
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 5 FAN7621B ? pfm controller for half-bridge resonant converters electrical characteristics t a =25 c and lv cc =17v unless otherwise specified. symbol parameter test conditions min. typ. max. unit supply section i lk offset supply leakage current hv cc =v ctr 50 a i q hv cc quiescent hv cc supply current (hv cc uv+) - 0.1v 50 120 a i q lv cc quiescent lv cc supply current (lv cc uv+) - 0.1v 100 200 a i o hv cc operating hv cc supply current (rms value) f osc =100khz, v con > 0.6v, c load =1nf 5 8 ma no switching, v con < 0.4v 100 200 a i o lv cc operating lv cc supply current (rms value) f osc =100khz, v con > 0.6v, c load =1nf 6 9 ma no switching, v con < 0.4v 2 4 ma uvlo section lv cc uv+ lv cc supply under-voltage positive going threshold (lv cc start) 11.2 12.5 13.8 v lv cc uv- lv cc supply under-voltage negative going threshold (lv cc stop) 8.90 10.00 11.10 v lv cc uvh lv cc supply under-voltage hysteresis 2.5 v hv cc uv+ hv cc supply under-voltage positive going threshold (hv cc start) 8.2 9.2 10.2 v hv cc uv- hv cc supply under-voltage negative going threshold (hv cc stop) 7.8 8.7 9.6 v hv cc uvh hv cc supply under-voltage hysteresis 0.5 v oscillator & feedback section v condis control pin disable threshold voltage 0.36 0.40 0.44 v v conen control pin enable threshold voltage 0.54 0.60 0.66 v v rt v-i converter threshold voltage r t =5.2k 1.5 2.0 2.5 v f osc output oscillation frequency 94 100 106 khz dc output duty cycle 48 50 52 % f ss internal soft-start initial frequency f ss =f osc +40khz, r t =5.2k 140 khz t ss internal soft-start time 2 3 4 ms output section i source peak sourcing current hv cc =17v 250 360 ma i sink peak sinking current hv cc =17v 460 600 ma t r rising time c load =1nf, hv cc =17v 65 ns t f falling time 35 ns v hoh high level of high-side gate driving signal (v hvcc -v ho ) i o =20ma 1.0 v v hol low level of high-side gate driving signal 0.6 v v loh high level of high-side gate driving signal (v lvcc -v lo ) 1.0 v v lol low level of high-side gate driving signal 0.6 v
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 6 FAN7621B ? pfm controller for half-bridge resonant converters electrical characteristics (continued) t a =25 c and lv cc =17v unless otherwise specified. symbol parameter test conditions min. typ. max. unit protection section i olp olp delay current v con =4v 3.8 5.0 6.2 a v olp olp protection voltage v con > 3.5v 4.5 5.0 5.5 v v ovp lv cc over-voltage protection lv cc > 21v 21 23 25 v v aocp aocp threshold voltage -1.0 -0.9 -0.8 v t bao aocp blanking time 50 ns v ocp ocp threshold voltage -0.64 -0.58 -0.52 v t bo ocp blanking time (2) 1.0 1.5 2.0 s t da delay time (low-side) detecting from v aocp to switch off (2) 250 400 ns t sd thermal shutdown temperature (2) 110 130 150 c i su protection latch sustain lv cc supply current lv cc =7.5v 100 150 a v prset protection latch reset lv cc supply voltage 5 v dead-time control section d t dead time 350 ns note: 2. these parameters, although guarant eed, are not tested in production.
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 7 FAN7621B ? pfm controller for half-bridge resonant converters typical performance characteristics these characteristic graphs are normalized at t a =25oc. 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c temp ( o c) 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 normalized at 25 o c figure 4. low-side mosfet duty cycle vs. temperature figure 5. switching fre quency vs. temperature 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c figure 6. high-side v cc (hv cc ) start vs. temperature figure 7. high-side v cc (hv cc ) stop vs. temperature 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c figure 8. low-side v cc (lv cc ) start vs. temperature figure 9. low-side v cc (lv cc ) stop vs. temperature
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 8 FAN7621B ? pfm controller for half-bridge resonant converters typical performance characteristics (continued) these characteristic graphs are normalized at t a =25oc. 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c figure 10. olp delay current vs. temperature figure 11. olp protection voltage vs. temperature 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c figure 12. lv cc ovp voltage vs. temperature figure 13. r t voltage vs. temperature 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c 0.9 0.95 1 1.05 1.1 -50 -25 0 25 50 75 100 temp ( o c) normalized at 25 o c figure 14. con pin enable voltage vs. temperature figure 15. ocp voltage vs. temperature
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 9 FAN7621B ? pfm controller for half-bridge resonant converters functional description 1. basic operation : FAN7621B is designed to drive high-side and low-side mosfets complementarily with 50% duty cycle. a fixed dead time of 350ns is introduced between consecutive transitions , as shown in figure 16. high-side mosfet gate drive low-side mosfet gate drve dead t ime time figure 16. mosfets gate drive signal 2. internal oscillator : FAN7621B employs a current- controlled oscillator, as shown in figure 17. internally, the voltage of r t pin is regulated at 2v and the charging / discharging current for the oscillator capacitor, c t , is obtained by copying the current flowing out of r t pin (i ctc ) using a current mirror. therefore, the switching frequency increases as i ctc increases. figure 17. current controlled oscillator 3. frequency setting : figure 18 shows the typical voltage gain curve of a resonant converter, where the gain is inversely proportional to the switching frequency in the zvs region. the output voltage can be regulated by modulating the switching frequency. figure 19 shows the typical circuit configuration for r t pin, where the opto-coupler transistor is connected to the r t pin to modulate the switching frequency. 0.6 0.8 1.0 1.2 1.4 1.6 1.8 gain 140 150 60 70 80 90 100 110 120 130 frequency (khz) f min f normal f max f iss soft-sta rt figure 18. resonant converter typical gain curve r sense FAN7621B v cc lv cc rt con cs sg pg ctr hv cc ho lo r max r min r ss c ss figure 19. frequency control circuit the minimum switching frequency is determined as: min min 5.2 100( ) k f khz r = (1) assuming the saturation voltage of opto-coupler transistor is 0.2v, the maximum switching frequency is determined as: max min max 5.2 4.68 ()100() kk fkhz rr =+ (2) to prevent excessive inrush current and overshoot of output voltage during startup, increase the voltage gain of the resonant converter progressively. since the voltage gain of the resonant converter is inversely i ctc + - + - 3v 1v -q q r s f/ f 2i ctc v r ef i ctc 2v + - counte r (1 / 4) r t 8 gate dr ive c t
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 10 FAN7621B ? pfm controller for half-bridge resonant converters proportional to the switching frequency, the soft-start is implemented by sweeping down the switching frequency from an initial high frequency ( f iss ) until the output voltage is established. the soft-start circuit is made by connecting r-c series network on the r t pin, as shown in figure 19. FAN7621B also has an internal soft-start for 3ms to reduce the current overshoot during the initial cycles, which adds 40khz to the initial frequency of the external soft-start circuit, as shown in figure 20. the initial frequency of the soft-start is given as: min 5.2 5.2 ( ) 100 40 ( ) iss ss kk f khz rr ? =++ (3) it is typical to set the initial (soft-start) frequency of two ~ three times the resonant frequency ( f o ) of the resonant network. the soft-start time is three to four times the rc time constant. the rc time constant is as follows: ss ss ss trc =? (4) f s time control loop take over 40khz f iss figure 20. frequency sweeping of soft-start 4. control pin : the FAN7621B has a control pin for protection, cycle skipping, and remote on/off. figure 21 shows the internal block diagram for control pin. olp lv cc good 6 con lv cc ovp + - + - -q q r s auto-restart protection + - 0.4 / 0.6v 5v 23v lv cc i olp stop switching figure 21. internal block of control pin protection : when the control pin voltage exceeds 5v, protection is triggered. detailed applications are described in the protection section. pulse skipping : FAN7621B stops switching when the control pin voltage drops below 0.4v and resumes switching when the control pin voltage rises above 0.6v. to use pulse-skipping, the control pin should be connected to the opto-coupler collector pin. the frequency that causes pulse skipping is given as: () khz 100 x r k 16 . 4 r k 2 . 5 max min skip + = (5) FAN7621B v cc lv cc rt con cs sg pg ctr hv cc ho lo r max r min r ss c ss figure 22. control pin configuration for pulse skipping remote on / off : when an auxiliary power supply is used for standby, the main power stage using FAN7621B can be shut down by pulling down the control pin voltage, as shown in figure 23. r1 and c1 are used to ensure soft-start when switching resumes. figure 23. remote on / off circuit 5. protection circuits : the FAN7621B has several self- protective functions, such as overload protection (olp), over-current protection (ocp), abnormal over-current protection (aocp), over-voltage protection (ovp), and thermal shutdown (tsd). olp, ocp, and ovp are auto-restart mode protections; while aocp and tsd are latch-mode protections, as shown in figure 24.
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 11 FAN7621B ? pfm controller for half-bridge resonant converters auto-restart mode protection : once a fault condition is detected, switching is terminated and the mosfets remain off. when lv cc falls to the lv cc stop voltage of 10.0v, the protection is reset. FAN7621B resumes normal operation when lv cc reaches the start voltage of 12.5v. latch-mode protection : once this protection is triggered, switching is terminated and the gate output signals remain off. the latch is reset only when lv cc is discharged below 5v. figure 24. protection blocks current sensing using resistor : FAN7621B senses drain current as a negative voltage, as shown in figure 25 and figure 26. half-wave sensing allows low power dissipation in the sensing resistor, while full-wave sensing has less switching noise in the sensing signal. r sense FAN7621B lv cc rt con cs sg pg ctr hv cc ho lo c dl v cs i ds i ds v cs figure 25. half-wave sensing r sense FAN7621B lv cc rt con cs sg pg ctr hv cc ho lo c dl v cs i ds i ds v cs figure 26. full-wave sensing current sensing using res onant capacitor voltage : for high-power applications, current sensing using a resistor may not be available due to the severe power dissipation in the resistor. in that case, indirect current sensing using the resonant capacitor voltage can be a good alternative because the amplitude of the resonant capacitor voltage (v cr p-p ) is proportional to the resonant current in the primary side (i p p-p ) as: 2 pp p pp cr s r i v f c ? ? = (6) l v cc good 12 1 0 /12.5v v r e f internal bias lv cc good lv cc olp ov p + - -q q r s f/f lv cc <5v latch protection -q q r s f/ f aut o-re start protecti on shutdo w n con 20 k o cp ao cp tsd
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 12 FAN7621B ? pfm controller for half-bridge resonant converters to minimize power dissipation, a capacitive voltage divider is generally used for capacitor voltage sensing, as shown in figure 27. FAN7621B lv cc rt con cs sg pg ctr hv cc ho lo c dl i p c sense v sense c b 100 i p v cr v sense v cr p-p v sense pk delay d d trc = pk sense b pp cr sense b vc vcc ? = + 2 pk sense con v v = v con v sense pk figure 27. current sensing using resonant capacitor voltage 5.1 over-current protection (ocp) : when the sensing pin voltage drops below -0.6v, ocp is triggered and the mosfets remain off. this protection has a shutdown time delay of 1.5s to prevent premature shutdown during startup. 5.2 abnormal over-current protection : (aocp) : if the secondary rectifier diodes are shorted, large current with extremely high di/dt can flow through the mosfet before ocp or olp is triggered. aocp is triggered without shutdown delay when the sensing pin voltage drops below -0.9v. this protection is latch mode and reset when lv cc is pulled down below 5v. 5.3 overload protection (olp) : overload is defined as the load current exceeding its normal level due to an unexpected abnormal event. in this situation, the protection circuit should trigger to protect the power supply. however, even when the power supply is in the normal condition, the overload situation can occur during the load transition. to avoi d premature triggering of protection, the overload protection circuit should be designed to trigger only after a specified time to determine whether it is a tr ansient situation or a true overload situation. figure 27 shows a typical overload protection circuit. by sensi ng the resonant capacitor voltage on the control pin, the overload protection can be implemented. using rc time constant, shutdown delay can be also introduced. the voltage obtained on the control pin is given as: 2( ) pp b con cr bsense c vv cc ? = + (7) where v cr p-p is the amplitude of the resonant capacitor voltage. 5.4 over-voltage protection : (ovp) : when the lv cc reaches 23v, ovp is triggered . this protection is used when auxiliary winding of the transformer to supply v cc to the controller is utilized. 5.5 thermal shutdown (tsd) : if the temperature of the junction exceeds approximately 130 c, the thermal shutdown triggers.
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 13 FAN7621B ? pfm controller for half-bridge resonant converters 6. pcb layout guideline : duty imbalance problems may occur due to the radiated noise from main transformer, the inequality of the secondary-side leakage inductances of main transformer, and so on. among them, it is one of the dominant reasons that the control components in the vicinity of r t pin are enclosed by the primary current flow pattern on pcb layout. the direction of the magnetic field on the components caused by the primary current flow is changed when the high-and-low side mosfet turns on by turns. the magnetic fields with opposite direction from each other induce a current through, into, or out of the r t pin, which makes the turn- on duration of each mosfet different. it is strongly recommended to separate the control components in the vicinity of r t pin from the primary current flow pattern on pcb layout. figure 28 shows an example for the duty- balanced case. the yellow and blue lines show the primary current flows when the lower-side and higher- side mosfets turns on, respectively. the primary current does not enclose any component of controller. in addition, it is helpful to reduce the duty imbalance to make the loop configured between con pin and opto- coupler as small as possible, as shown in the red line in figure 28. figure 28. example for duty balancing
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 14 FAN7621B ? pfm controller for half-bridge resonant converters typical application circuit (half-b ridge llc resonant converter) application device input voltage range rated output power output voltage (rated current) lcd tv FAN7621B 390v dc (340~400v dc ) 192w 24v-8a features ? high efficiency ( >94% at 400v dc input) ? reduced emi noise through zero-voltage-switching (zvs) ? enhanced system reliability with various protection functions fan7621 f101 3.15a/250v lvcc rt con cs sg pg ct r hvcc vin=340~400vdc ho lo c301 c101 220uf/ 450v vcc=16~20vdc r109 1m r110 1m r111 45k c105 0.33uf r108 10k r103 400k u5 r112 10k u4 zd101 6.8v jp5 0 r202 1k d101 1n4937 r11 3 3.3 r11 4 3.3 d10 2 1n4148 d10 2 1n4148 r115 10k r116 10k q1 fcpf11n60f q2 fcpf11n60f c106 150nf r104 5.1k u2 r105 7.5k r107 7.7k c107 10uf c111 680pf c104 open c108 12nf c103 100pf r102 1k r101 0.2 jp1, 0 jp2, 0 jp3, 0 jp4, 0 vo c1 02 22nf c110 open d202 fypf2010dn d201 fypf2010dn r201 10k u2 r203 33k c203 47nf r205 2k r204 62k c204 12nf r205 7k c201 2000uf / 35v c202 2000uf/ 35v eer3542 figure 29. typical application circuit
? 2009 fairchild semiconductor corporation www.fairchildsemi.com FAN7621B ? rev. 1.0.1 15 FAN7621B ? pfm controller for half-bridge resonant converters typical application circuit (continued) usually, llc resonant converters require large leakage i nductance value. to obtain a large leakage inductance, sectional winding method is used. ? core: ec35 (ae=106 mm 2 ) ? bobbin: ec35 (horizontal) ? transformer model number: snx-2468-1 ec35 n p 2 6 9 12 10 n s2 13 n s1 figure 30. transfor mer construction pins (s f) wire turns note n p 6 2 0.08 88 (litz wire) 36 n s1 12 9 0.08 234 (litz wire) 4 bifilar winding n s2 10 13 0.08 234 (litz wire) 4 bifilar winding pins specifications remark primary-side inductance (l p ) 2 6 550 h 10% 100khz, 1v primary-side effective leakage (l r ) 2 6 110 h 10% short one of the secondary windings for more detailed information regarding the transformer, visit http://www.santronics-usa.com/documents.html or contact sales@santronics-usa.com or +1-408-734-1878 (sunnyvale, california usa).
1 8 9 16 pin #1 ident. a. conforms to eiaj edr-7320 registration, established in b. dimensions are in millimeters. c. dimensions are exclusive of burrs, mold flash, and tie bar extrusions. 1 8 9 16 2 7 10 15 10.30 10.10 5.40 5.20 1.90 1.70 0.51 0.35 1.27 typ 9.27 typ 5.01 typ 1.27 typ notes: 0.60 typ see detail a gage plane 0.25 seating plane 0-8 typ min 0.25 1.25 3.9 7.8 0.47 typ 2.1 max (2.13 typ) 0.25 0.15 7 typ d. drawing filename: mkt-m16drev5 all lead tips all lead tips 0.16 0.14 december, 1998. 0.2 c b a 0.1 c 0.12 c a -a- -b-
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