S m a l l S i g n a l O ptim O S M O S F E T i n L o w P o w e r D C / D C c o n v e r t e r s

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1 Application Note AN 0- V.0 ecember 0 S m a l l S i g n a l O ptim O S M O S F E T i n L o w o w e r C / C c o n v e r t e r FAT MM AS SE radeep Kumar Tamma

2 Application Note AN 0- V.0 ecember 0 Edition ublihed by nfineon Technologie Autria AG 9500 Villach, Autria nfineon Technologie Autria AG 0. All Right Reerved. Attention pleae! THE NFORMATON GVEN N THS ALCATON NOTE S GVEN AS A HNT FOR THE MLEMEN- TATON OF THE NFNEON TECHNOLOGES COMONENT ONLY AN SHALL NOT BE REGARE AS ANY ESCRTON OR WARRANTY OF A CERTAN FUNCTONALTY, CONTON OR QUALTY OF THE NFNEON TECHNOLOGES COMONENT. THE RECENT OF THS ALCATON NOTE MUST VERFY ANY FUNCTON ESCRBE HEREN N THE REAL ALCATON. NFNEON TECHNOLOGES HEREBY SCLAMS ANY AN ALL WARRANTES AN LABLTES OF ANY KN (NCLUNG WTHOUT LMTATON WARRANTES OF NON-NFRNGEMENT OF NTELLECTUAL ROERTY RGHTS OF ANY THR ARTY) WTH RESECT TO ANY AN ALL NFORMATON GVEN N THS ALCATON NOTE. nformation For further information on technology, delivery term and condition and price pleae contact your nearet nfineon Technologie Office ( Warning ue to technical requirement component may contain dangerou ubtance. For information on the type in quetion pleae contact your nearet nfineon Technologie Office. nfineon Technologie Component may only be ued in life-upport device or ytem with the expre written approval of nfineon Technologie, if a failure of uch component can reaonably be expected to caue the failure of that life-upport device or ytem, or to affect the afety or effectivene of that device or ytem. Life upport device or ytem are intended to be implanted in the human body, or to upport and/or maintain and utain and/or protect human life. f they fail, it i reaonable to aume that the health of the uer or other peron may be endangered.

3 Application Note AN 0- V.0 ecember 0 Table of content ntroduction... 4 Application Example Application Boundary condition Application circuit configuration... 5 Review of Loe in a C/C converter MOSFET Switching Loe MOSFET Gate Loe MOSFET Output Loe MOSFET Conduction Loe Calculation of MOSFET Loe in the application Comparion and Summary...

4 Application Note AN 0- V.0 ecember 0 ntroduction nfineon new 60V cla Small Signal OptiMOS 606 family will be available in TSO-6, SOT-89 and SC59 package. The low Q g and low R (on) make the OptiMOS 606 uitable for low power C/C converter and cell balancing in Battery Energy Control Module (BECM). Alo the logic level gate enable it to be eaily interfaced directly with MCU / igital circuit. A all product are qualified to AEC Q0, they are ideally uitable for automotive and high quality demanding application. Thi application note illutrate the benefit of BSL606SN (TSO-6 package) in low power C/C application. The main feature of BSL606SN are hown in the table below. arameter Symbol Condition Value Unit Continuou drain current T A = 5 C 4.5 A rain-ource breakdown voltage V (BR)S V GS =0 V, = 50 µa V Gate threhold voltage V GS(th) V = 0 V, = 5 µa..8. rain-ource on-tate reitance R (on) V GS =4.5 V, =.6A mω Gate to ource charge Q g V = 48 V, = 4.5 A,.9.5 nc Gate to drain charge Q gd V GS = 0 to 5 V.0.5 Gate charge total Q g Table : BSL606SN Main Feature Application Example A good example of a low power C/C converter i an LE power upply. n Automotive, LE lighting i now common. A typical automotive lighting application i the aytime Running Light (RL) function uch a the one hown in the picture below. Figure : RL function example 4

5 Application Note AN 0- V.0 ecember 0. Application Boundary condition An example of the application boundary condition for a RL function i given below. The um of the LE forward voltage (C/C converter output voltage V OUT ) i approximately 5 V. The upply input voltage V N i pecified in the range of 8 V to 6 V. The nominal value i V. The LE current or the output current of the C/C converter OUT hould be 400 ma. Boot configuration i ued with a witching frequency of around 400 khz operated in continuou conduction mode.. Application circuit configuration The figure below illutrate the Boot configuration of a RL application. Figure : Boot circuit configuration A ummary of the application boundary condition, which hould be the bai for the calculation of the loe in the application, are preented in the table below Symbol Value Unit Name V N V Nominal input Voltage V OUT 5 V LE forward voltage OUT 0.4 A LE Current F 400 khz Switching Frequency ΔV OUT 00 mv Max. ripple voltage on V OUT Δ L% 0 % k-k inductor Ripple current. Table : Application Boundary condition 5

6 Application Note AN 0- V.0 ecember 0 Review of Loe in a C/C Converter The efficiency of a C/C converter i a meaure of the ratio of the output power upplied to the load with repect to the input power. The input power i equal to the load power plu the converter loe. A C/C converter ha it loe in it control circuit and magnetic, out of which witching loe are the greatet contributor. Thee loe are briefly dicued in the following ub-ection.. MOSFET Switching Loe Switching loe occur due to the poitive product of current through the MOSFET and voltage acro it during witching tranition. The witching loe occur twice for every witching period during turn-on and turn-off. The figure below illutrate current and voltage during turn-on. Figure : MOSFET turn on waveform 6

7 Application Note AN 0- V.0 ecember 0 Uing linear approximation of the waveform, the power lo component for the repective interval can be etimated. The etimated power component in interval T and T are given by: T V V T F F The total turn-on witching loe are the um of the two component and are given by: on T T V F T V F SW ( on) () () () Where T SW (on) i the turn-on time for the MOSFET it depend upon the gate drive voltage. The average gate drive current during T and T, T and T are given by: V cc 0.5 V pl V th T Rtot V cc V pl T Rtot V cc = gate driver power upply. R tot = total gate reitance. Auming that g, T charge the input capacitor of the MOSFET from V th to V pl and g,t i the dicharge current of the gate to drain capacitor while the drain voltage change from V to 0 then the approximate T and T are given by: T C i T C r V pl V th T V T (4) (5) (6) (7) The turn-on time, T SW (on) i the um of T and T and i given by: T SW( on) C T T i V pl T V th C r V T (8) Similarly the turn-off witching loe can be etimated and are given by: off TSW( off ) V F (9) Thu the total witching loe are the um of turn-on loe and turn-off loe. 7

8 Application Note AN 0- V.0 ecember 0 T SW( on) TSW( off V F w on off ) Where, T SW (off) i the turn-off time for MOSFET. (0). MOSFET Gate Loe Energy i required in order to charge and dicharge the gate capacitance of the MOSFET for each witching period. Thi energy i uually diipated through gate erie reitance in the gate driver circuit. Thu the gate loe are given by: g Q g V cc F () Q G = total gate charge, V cc = gate driver power upply voltage and F = witching frequency of the converter.. MOSFET Output Loe The output loe are the energy loe when the MOSFET output drain to ource capacitance i dicharging during turn-on. Thu the output loe are given by: out () C V F C = MOSFET output rain to Source capacitance..4 MOSFET Conduction Loe n the on-tate, MOSFET do not behave like an ideal witch with zero impedance, but intead they have a mall reitance typically called R (on). ue to thi reitance there will be power loe in the MOSFET and thee are calculated by: cond R ( on), RMS () d, RMS = RMS value of the current through the MOSFET. The RMS value can be calculated by the current waveform in the MOSFET. When the converter i operating in continuou conduction mode the MOSFET current wave form will be a hown in the figure below. n the figure, L, avg i the average current in the inductor, T i the witching period, i the duty ratio and Δ L i the ripple current in the inductor 8

9 Application Note AN 0- V.0 ecember 0 Figure 4: Current through MOSFET When the MOSFET i turned on, the current within it i equal to the current in the inductor. Thu the RMS value of the MOSFET current i given by:, RMS. L, avg ( L ) (4) So the total MOSFET loe will be the um of all loe MOSFET w g out cond (5) 4 Calculation of MOSFET Loe in the Application From the above ection, BSL606SN loe can be etimated uing the pecified application value from Table. Auming the MOSFET i driven by a 5 V gate drive power upply with 0 Ohm of total gate reitance and the input voltage i 8 V the following i the cae. The witching loe of BSL606SN are: T SW( on) TSW( off V F w ) V 0.4A 4000 Hz 0. W w 009 (6) 9

10 Application Note AN 0- V.0 ecember 0 T SW (on) and T SW (off) are calculated a dicued in ection.. The gate loe of BSL606SN are: g Q g V cc F 9 g.80 C5V 4000 Hz W (7) The output loe of BSL606SN are: out C V F Co CrV F V 4000 Hz 690 F 5V 4000 Hz 0. W out 0 (8) The conduction loe of BSL606SN are: cond R ( on), RMS L 0.4A, RMS. L, avg A. 0A VOUT VN For the boot converter the duty ratio and the average current through the inductor i V equal to the average input current for the converter and i given by inductor ripple current Δ L i given in table. OUT N OUT, avg L, avg and the.0a 0. W cond (9) 0

11 Loe (mw) Small Signal OptiMOS 606 MOSFET in Application Note AN 0- V.0 ecember 0 Thu the total loe of BSL606SN are ummarized in the table below BSL606SN Conduction Loe cond 70 mw Switching Loe w 09 mw Gate Loe g 08 mw Output Loe out 0 mw Total MOSFET loe MOSFET 08 mw Table : BSL606SN loe in application 5 Comparion and Summary BSL606SN loe are compared with an automotive qualified competitor part of the ame voltage cla. The figure below illutrate the different loe in the repective device. Total Loe BSL606SN competitor part o drv w con Figure 5: Lo comparion The chart how that there are ignificantly le loe in the converter when BSL606SN i ued in comparion to that of the competitor part. The benefit of uing BSL606SN in low power C/C converter can be ummaried a follow: The gate loe are comparitively very mall in BSL606SN. Thi mean that the gate require little current even at logic level to turn it on. Thi make it eay to interface to MCU/ digital circuit. The witching loe are very mall with BSL606SN. Thi give the flexibility of increaing the witching frequency which in turn increae the tranient performance. With the increae in witching frequency the inductance can be decreaed which in turn decreae the total converter ize and cot.