AN2650 Application note

Transcription

1 AN2650 Applicaion noe L9942 sepper moor driver for bipolar sepper moors Inroducion The L9942 is an inegraed sepper moor driver for bipolar sepper moors. The device is designed for auomoive applicaions, such as headlamp leveling, seerable lighs and adapive fron lighing. Oher applicaions, such as venilaion and air condiioning flap and hrole posiioning are also possible uses for he L9942. The device drives bipolar sepper moors wih high-efficiency and smooh operaion. Microsepping is he preferred mode o provide low-noise operaion since his echnique eliminaes he effecs of mechanical resonances, which can lower he moor orque. A moor sall deecion capabiliy allows posiion alignmen wihou an exernal sensor, while is sep couner is addressable via an SPI as well as by a separae inpu, o preven he SPI overloading when running muliple moors simulaneously. November 2007 Rev 1 1/24

2 Conens AN2560 Conens Inroducion Typical applicaion schemaic Calculaion of he buffer capacior Cbuffer Low drop reverse polariy proecion Shored coil deecion Conclusion SPI Faul bi SPI communicaion monioring Decay modes Slow decay Fas Decay Advanced decay modes Mixed decay Auo decay Sall deecion Inernal funcionaliy (simplified) How o deermine he sall hreshold a bench es Duy cycle for curren regulaion Minimum duy cycle Maximum duy cycle Power dissipaion Saic Saic freewheeling Dynamic slew rae power dissipaion Power dissipaion for one PWM phase /24

3 AN2560 Conens 8 PCB fooprin proposal Revision hisory /24

4 Lis of ables AN2560 Lis of ables Table 1. Phase couner values for fas decay Table 2. Documen revision hisory /24

5 AN2560 Lis of figures Lis of figures Figure 1. Applicaion schemaic diagram Figure 2. Low drop reverse polariy proecion Figure 3. Sepping modes (Auo decay mode, fas decay wihou delay ime) Figure 4. Auo decay, fas decay wihou delay ime a phase 0 and Figure 5. SPI ransfer iming diagram Figure 6. Slow decay Figure 7. Fas decay Figure 8. Mixed decay Figure 9. Auo decay Figure 10. Sall deecion funcion overview Figure 11. Cross curren proecion ime and slew rae for maximum DC Figure 12. Curren flow and volage drop during fas decay Figure 13. Power SSO24 solder mask layou (all values in mm) Figure 14. Power SSO24 solder mask opening (all values in mm) /24

6 Typical applicaion schemaic AN Typical applicaion schemaic Figure 1. Applicaion schemaic diagram V ba 5V V reg 100n C buffer 100n Vcc CP µc ou ou in in ou ou ou STEP EN QA 1 2 PWM QA 2 23 DO L9942 DI CLK QB 1 11 CSN QB 2 14 RREF 2n2 2n2 2n2 SM 6k8 GND TEST PGND PGND n2 GND PGND The L9942 is driven by a microconroller via he SPI (DO, DI, CLK, and CSN), STEP and EN pins. Addiional informaion is provided from he PWM pin. The sepper moor driver is supplied from a 5 V volage regulaor and he reverse polariy proeced. I is necessary o use a sabilizaion capacior (wih a minimum value of minimum 100 nf) as close as possible a he Vcc pin. For he sabilizaion of he supply pin and o absorb moor energy, an elecrolyic capacior C buffer, wih a minimum value as calculaed in Secion 1.1, mus be used. Because he moor currens are supplied via he -pins, all -pins mus have a low ohmic connecion o he supply volage. For he same reason, all GND and PGND pins mus have a low ohmic connecion o he sysem ground. A sar ground concep wih separae lines for GND and PGND is recommended. A he charge pump pin, a capacior wih 100 nf o is recommended. To improve he EMI behavior, i is recommended o have 2.2 nf capaciors as close as possible o he moor oupu pins, Qxy. Shor moor connecion wires also improve he EMI behavior. The inernally-used reference volage depends upon he value of he reference resisor, posiioned beween he pin RREF and GND. Consequenly, he precision of he L9942 depends upon he value of he reference resisor. One possible value for his resisor is 6.8 kω. 6/24

7 AN2560 Typical applicaion schemaic Due o he srucure of he BCD process, he slug of he device is conneced inernally o PGND and mus also be conneced exernally o PGND. 1.1 Calculaion of he buffer capacior C buffer The sepper moor driver L9942 is usually designed in an environmen similar o ha shown in Figure 1. During moor operaion, elecrical energy is sored in he moor coils. If he moor shus down, his energy is fed back o he supply volage. Thus, here is a volage increase a, which may cause an elecrical oversress of he L9942. To avoid damage o he L9942, he value of he buffer capacior C buffer mus be chosen carefully. The energy balance can be calculaed from: C 2 buffer V s1 2 L moor 2 2 V s I C moor = V s2 buffer L 2 moor I moor -- C 2 buffer V s2 V s2 = 2 L moor 2 V s I C moor buffer Noe: From his equaion, i is possible o conclude: he volage 2 mus no exceed he maximum raing of he L9942 if an over volage shu down mus be avoided, he volage 2 mus no exceed he minimum over volage hreshold. As a general recommendaion, STMicroelecronics recommend a minimum buffer capacior of 47 µf. The ripple a during normal moor operaion should be beween 5% and 10%. 7/24

8 Typical applicaion schemaic AN Low drop reverse polariy proecion Figure 2. Low drop reverse polariy proecion V ba 100k 100k 100n STD17NF03LT C buffer CP L9942 L9942 Vreg As shown in Figure 2 he charge pump pin can be used for a low drop reverse polariy proecion. The charge pump pin can also be used for oher devices in he same applicaion. Because of he addiional gae capaciy, he charge pump ramps up more slowly han wihou he addiional MOSFET gae. 8/24

9 AN2560 Shored coil deecion 2 Shored coil deecion During free-wheeling ime, he L9942 can use several decay modes ha are programmable by he SPI. However, only on Auo decay, fas decay wihou delay ime i is possible o deec shored coil because, during free-wheeling ime, boh opposie ransisors (HS and LS) are swiched on and high curren can rise. During free wheeling he curren in he oupu sage is moniored, bu no regulaed, wih PWM. Because of his, he shor overcomes he over curren filer ime and can be deeced. In oher decay modes, he decay can periodically change during wheeling of he moor (for example, every 200 ms) o Auo decay, fas decay wihou delay ime for few microseconds and han change i back o previous value. This can be done in one clock sep. The decay mode canno be changed a all values of he phase couner because fas decay is no acive during he whole period bu only during decreasing curren phase in he coil (during he rising curren phase, he coil is acive slow decay mode). A deailed explanaion of Auo decay, fas decay wihou delay ime for all sep modes is given in Figure 3. Figure 3. Sepping modes (Auo decay mode, fas decay wihou delay ime) Phase Couner Full-Sep Mode, DIR= Phase Couner 24 Full-Sep Mode, DIR= Curren Driver A Curren Driver A Curren Driver B Fas Decay Sep CLK Slow Decay Curren Driver B Fas Decay Slow Decay Sep CLK Phase Couner Curren Driver A Half-Sep Mode, DIR= Fas Decay Slow Decay Curren Driver B Sep CLK Mini-Sep Mode, DIR=0 Phase Couner Curren Driver A Curren Driver B Sep CLK Phase Couner Curren Driver A Curren Driver B Sep CLK Fas Decay Slow Decay HSA Fas Decay HSB1 Micro-Sep Mode, DIR=0 HSB2 HSA1 Slow Decay Half-Sep Mode, DIR=1 Phase Couner Curren Driver A Fas Decay Slow Decay Curren Driver B Sep CLK Phase Couner Curren Driver A Curren Driver B Sep CLK Phase Couner Curren Driver A Curren Driver B Sep CLK Mini-Sep Mode, DIR= Fas Decay Micro-Sep Mode, DIR=1 Fas Decay HSB1 HSA Slow Decay HSB HSA Slow Decay Table 1 shows Phase Couner values where fas decay is acive. 9/24

10 Shored coil deecion AN2560 Table 1. Phase couner values for fas decay Sep Mode Bridge DIR=0 DIR=1 Full sep Half sep Mini sep Micro sep A (8) (24) (16 (1) ) (0 (1) ) B (0) (16) (24 (1) ) (8 (1) ) A (8, 12) (24, 28 (20, 16 (1) ) (4, 0 (1) ) B (0, 4) (16, 20) (28, 24 (1) ) (12, 8 (1) ) A (8, 10,12,14) (24,26,28,30) (22,20,18,16 (1) ) (6, 4, 2, 0 (1) ) B (0, 2, 4, 6) (16,18,20,22) (30,28,26,24 (1) ) (14,12,10, 8 (1) ) A B (8,9,10,11,12,13,14,15) (24,25,26,27,28,29,30,31) (0, 1, 2, 3, 4, 5, 6, 7) (16,17,18,19,20,21,22,23) (23,22,21,20,19,18,17,16 (1) ) (7, 6, 5, 4, 3, 2, 1, 0 (1) ) (31,30,29,28,27,26,25,24 (1) ) (15,14,13,12,11,10, 9, 8 (1) ) 1. Curren profile_0 mus be greaer han Conclusion To deec shored coil in boh bridges (A and B) and for all sep modes (Full, Half, Mini and Micro), i is necessary o change decay mode o Auo decay, fas decay wihou delay ime a phase couner values of 0 and 8 (or 16 and 24). For he opposie direcion, DIR=1 can also use 0 and 8 (or 16 and 24) bu he ampliude of curren profile_0 mus be greaer han 0. This configuraion is illusraed in Figure 4. Figure 4. Auo decay, fas decay wihou delay ime a phase 0 and 8 200ms phase Auo decay, fas decay wihou delay ime a phase 0 and 8 (DIR=0) Noe: Anoher possibiliy is o change he decay mode for Micro, Mini and Half Sep mode a phase couner values of 4 and 12 and for Full Sep mode a phase couner values of 0 and 8. 10/24

11 AN2560 SPI 3 SPI 3.1 Faul bi Figure 5. SPI ransfer iming diagram CSN_HI,min CSN CSN high o low: DO enabled ime CLK DI DO Conrol and Saus Regiser DI: daa will be acceped on he rising edge of CLK signal acual daa A2 A1 A0 D12D11D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 DO: daa will change on he falling edge of CLK signal saus informaion D12D11D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 faul bi CSN low o high: acual daa is ransfered o regisers old daa faul bi acual daa new daa A2 A1 ime ime ime ime The firs hree bis of an SPI wrie frame are he regiser address. Thus, during his ime, i is no clear which regiser has o be wrien and read. This ime is used a he DO-pin o monior he or-funcion of all diagnosic funcions. The regiser read ou is sared wih he hird falling edge of he SPI CLK. The read ou is finished 13 falling edges laer and during he remaining ime, unil CSN is se o high, he orfuncion of all diagnosic funcions is moniored again. Using his mehod, he failure saus of he device can be checked wihou an SPI communicaion. CSN is only pulled o low for a shor while. 3.2 SPI communicaion monioring SPI communicaion monioring is described in he specificaion. However, for regiser 0 he following wo poins should be considered. 1. During SPI communicaion, monioring he STEP-pin mus no be used. This could cause he Phase Couner o be modified. 2. When no using he microsepping sep mode, no all Curren Profile Regisers are used. When sending a command o he Conrol Regiser 0 for SPI communicaion monioring wih a Phase Couner value ha no used in he seleced sep mode, he device will correc he Phase Couner value iself. In his case, SPI communicaion monioring will fail. 11/24

12 Decay modes AN Decay modes During he phase he curren in he moor coil increases. Afer an phase, an phase follows ha always sars wih he cross curren proecion ime (cc). The cross curren proecion ime is auomaically chosen wih he slew rae and is ypically in he range from 0.5 o 4 µs. Afer he cross curren proecion ime, a programmed decay mode follows. The basic decay modes of he sepper moor driver L9942 are: slow decay fas decay advanced decay modes, which are combinaions of he slow and fas decay modes. 4.1 Slow decay The slow decay mode realizes a minimum loss of energy in he moor coil. This means he curren decrease in he moor coil is slow. Slow decay is illusraed in Figure 6. Figure 6. Slow decay CC increase cross curren proecion slow decay U BE U Ron gnd gnd gnd 12/24

13 AN2560 Decay modes 4.2 Fas Decay The fas decay mode realizes a maximum loss of energy in he moor coil. This means he curren decrease in he moor coil is fas. Fas decay is illusraed in Figure 7. Figure 7. Fas decay CC increase cross curren proecion fas decay U BE U Ron gnd gnd gnd 4.3 Advanced decay modes Wih he sepper moor driver L9942, i is possible o combine he basic decay modes, slow and fas decay Mixed decay From he curren poin of view, for sepping down i is necessary o reduce he curren in he moor coil quickly. Therefore, a mosly slow decay is no useful because here is he danger ha he curren in he moor coil does no reach he new (lower) curren arge. Wih fas decay, he curren undershoo may be sronger han necessary; his generaes more EMI han necessary. A beer resul is obained by mixing fas decay wih slow decay. Mixed decay sars wih fas decay and swiches o slow decay; he poin for swiching beween he decay modes is programmable. Mixed decay is shown in Figure 8. 13/24

14 Decay modes AN2560 Figure 8. Mixed decay I Targe I II CC MD Mixed decay, fas decay unil curren undershoo In Figure 8, his behavior is shown wih graph I. Fas decay is driven unil he moor coil curren has undersho he arge curren and swiches o slow decay unil he end of he phase. Mixed decay, fas decay unil MD > 4(8) µs In Figure 8, his behavior is shown wih graph II. The ime MD is sared afer he cross curren proecion ime cc is over. Afer MD is finished he sepper moor driver swiches o slow decay. MD is programmable o 4µs or 8µs Auo decay If he curren in he moor coil is required o increase from sep o sep, i is sensible o save he curren in he moor coil. Therefore, he bes decay mode is slow decay (see Secion 4.1). If, on he oher hand, he curren in he moor coil should decrease from sep o sep, i is sensible o reduce he curren in he moor coil in a conrolled way, as described in Secion Therefore, he bes decay mode is mixed decay. The combinaion of slow decay for increasing curren from sep o sep and mixed decay for decreasing curren from sep o sep is auo decay. A combinaion of slow decay and pure fas decay is also possible bu his opion usually increases he EMI emission. In Figure 9, auo decay is shown for one of he moor coils wih micro sepping. For each sep, he appropriae curren profile regiser is also shown. Inernally, a poiner moves from a curren profile regiser o he nex curren profile regiser wih each SepCLK pulse. This sar from he regiser 0 and goes sep by sep o regiser 8 and hen back o regiser 0... When he poiner is going in he direcion from regiser 0 o 8, he L9942 uses slow decay. When he poiner is going from regiser 8 o 0, mixed or fas decay is seleced. 14/24

15 AN2560 Decay modes Figure 9. Auo decay auo decay slow decay fas or mixed decay curren profile regiser slow decay fas or mixed decay auo decay V SepCLK Auo decay, fas decay wihou delay ime Slow decay for curren profile regiser going up (0 8) plus pure fas decay (see also fas decay in Figure 7) for curren profile regiser decreasing (8 0). Auo decay, fas decay unil MD > 4(8) µs: Slow decay for curren profile regiser going up (0 8) plus mixed decay (see also mixed decay in Figure 8, graph II ) for curren profile regiser decreasing (8 0). Auo decay, fas decay unil curren undershoo Slow decay for curren profile regiser going up (0 8) plus mixed decay (see also mixed decay in Figure 8, graph I ) for curren profile regiser increasing (0 8). 15/24

16 Sall deecion AN Sall deecion The sall deecion funcion of he L9942 uses he reference drive of a sepper moor sysem, such as ha usually used in he sar up phase of a fron ligh levelling sysem. 5.1 Inernal funcionaliy (simplified) The back EMF of he permanen magneic roor of he sepper moor is he effec ha is used for he sall deecion funcion. If he moor is urning fas, he back EMF is high. Thus, he volage drop a he moor coils is low. Combined wih he inducance of he moor coils, i akes a long ime o reach he arge curren. Consequenly, his means a long duy cycle of he pulse widh modulaion (PWM). If he moor is sopped mechanically, he back EMF is zero. Thus, he volage drop a he moor coils is high. Combined wih he inducance of he moor coils, i akes a shor ime o reach he arge curren. This means a shor duy cycle of he PWM. As is shown in Figure 10, an inernal couner couns he duy cycle of he curren regulaion PWM. This value is compared wih a value given from he microconroller via he SPI. If his value is less han he one supplied by he microconroller, he sall deecion bi is se. Figure 10. Sall deecion funcion overview PWM duy cycle for cur. reg. PWM curren regulaion couning From SPI comp. sall deecion bi 16/24

17 AN2560 Sall deecion 5.2 How o deermine he sall hreshold a bench es There are four seps o deermine he sall hreshold. 1. Drive moor in an environmen wih parameers as in a possible sall siuaion. 2. Run he moor so ha i is urning coninually and increase he sall hreshold sep by sep unil he sall bi is se. This sall hreshold value is called he high value. 3. Wih he same elecrical condiions as before, sop he moor mechanically. Decrease he sall hreshold from he high value. Afer some seps he sall bi is rese. This sall hreshold value is called he low value. 4. The sall hreshold is he middle value beween he high value and he low value. 17/24

18 Duy cycle for curren regulaion AN Duy cycle for curren regulaion The duy cycle for curren regulaion is always swiched on for a minimum ime and has a maximum ime of less han 100%. 6.1 Minimum duy cycle The minimum duy cycle is he sum of he Glich filer delay ime, he Slew rae and he Cross curren proecion ime. The Slew rae and he Cross curren proecion ime are programmed wih he same bis. 6.2 Maximum duy cycle The maximum duy cycle is less hen 100%. The negligible off ime is relaed o he Cross curren proecion ime. Cross curren proecion ime is illusraed in Figure 11. Figure 11. Cross curren proecion ime and slew rae for maximum DC OUT Slew Rae B Slew Rae A T CC 18/24

19 AN2560 Power dissipaion 7 Power dissipaion The calculaion of he power dissipaion depends upon he seleced slew rae and decay mode of he device. In Figure 12 he se up was seleced wih a fas decay. Figure 12. Curren flow and volage drop during fas decay U Ron OUT-B OUT-A OUT-B OUT-A gnd gnd FW fas decay V OUT-A V OUT-B r/f PWM Pulse D For a rough calculaion of he power dissipaion, hree differen phases are seleced: 1. saic 2. saic free wheeling (FW), fas decay 3. dynamic on and off wih slew rae. 7.1 Saic Only he RDS,on of he high and low side swiches are used for generaing power dissipaion. 19/24

20 Power dissipaion AN Saic freewheeling Only he RDS,on of he high and low side swiches are used for free wheeling and generaing power dissipaion. 7.3 Dynamic slew rae power dissipaion During he H-bridge swiching, he volage and he curren chang in a riangular form wih he defined slew rae. 7.4 Power dissipaion for one PWM phase The emporary power dissipaions, explained above, are summed for he complee PWM phase. P P Puls r f P D Puls r f 2 r f = + FW P D SR D D P = P D 2 r f f r SR D D P = 2 R DS, I 2 D 2 r f r f + U I D D 20/24

21 AN2560 PCB fooprin proposal 8 PCB fooprin proposal Figure 13. Power SSO24 solder mask layou (all values in mm) 21/24

22 PCB fooprin proposal AN2560 Figure 14. Power SSO24 solder mask opening (all values in mm) 22/24

23 AN2560 Revision hisory 9 Revision hisory Table 2. Documen revision hisory Dae Revision Changes 2-Nov Iniial release. 23/24

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