Prepared by: Tom De Ryck ON Semiconductor Start. Figure 1. Full Step Mode

Transcription

1 How o Measure Bemf on he SLA-pin Prepared by: Tom De Ryck ON Semiconducor APPLICATION NOTE Absrac To enable he possibiliy o build very accurae sall and seploss algorihms as also orque adapive applicaions, AMIS 305xx has a Speed and Load Angle (SLA) pin which oupus a volage ha reflecs he Bemf (Back Elecro Magneic Force) volage of he moor. To preven incorrec use of he SLA pin, his applicaion noe describes how he moor driver should be operaed o measure he correc Bemf volage on he SLA pin. Inroducion The Bemf is sampled every so called coil curren zero crossing. Per coil 2 zero crossing posiions exis per elecrical period, resuling in a oal of 4 zero crossings per elecrical period. Or in shor, he Bemf volage can be measured 4 imes per elecrical period. Alhough he Bemf volage can be measured 4 imes per elecrical period, i does no mean ha i will be measured 4 imes. The Bemf volage will only be sampled by he moor driver if a microsep posiion is locaed on he coil curren zero crossing. Only hen a correc represenaion (Noe 1) of he Bemf volage can be measured on he SLA pin. If no microsep posiion is locaed on he coil curren zero crossing, an incorrec value will be measured on he SLA pin. Coil Curren Zero Crossings Nex figures display 4 of he in oal 7 sepping modes possible wih AMIS 305xx. I coil Sar Sar Figure 1. Full Sep Mode 1. The volage measured on he SLA pin only represens he Bemf volage. Depending on he SLA Gain seing (see Ref 1) he SLA volage will be equal o 1/2 or 1/4 of he real Bemf volage. Semiconducor Componens Indusries, LLC, 2010 Augus, 2010 Rev. 2 1 Publicaion Order Number: AND8399/D

2 I coil coil curren zero crossing Sar Sar coil curren zero crossing Figure 2. Half Sep Compensaed Mode I coil coil curren zero crossing Sar Sar coil curren zero crossing Figure 3. 1/4h Sepping Mode I coil coil curren zero crossing Sar IX Sar coil curren zero crossing Figure 4. 1/8 Sepping Mode As displayed in above figures, a microsep posiion is locaed on he coil curren zero crossing excep for full sep mode (Noe 2). Only if a microsep posiion is locaed on he coil curren zero crossing, a correc represenaion of he Bemf volage can be measured on he SLA pin. 2. See he Full Sep Sepping Mode secion for more info on full sep seppingmode. 2

3 The several sepping modes of AMIS 305xx offers a lo of flexibiliy bu a he same ime could also cause problems when no used in a correc way. Figure 5 displays wha could go wrong when swiching beween sepping modes is done in an incorrec way. Moor is in full sep posiion, sepping mode is 1/8 sepping NXT pulse is applied. 1/8 of a full sep is se. Sepping mode is changed o half sepping and several NXT pulses are applied Figure 5. Changing of Sepping Mode in an Incorrec Way Above figure demonsraes ha care should be aken when changing he sepping mode o a lower resoluion. When changing o a lower sepping mode, i is possible ha an offse is creaed resuling in no microsep posiion a he coil curren zero crossing. The sepper moor driver will no sample he Bemf volage and an incorrec represenaion of he Bemf volage will be measured on he SLA pin. Nex figure displays again half sepping bu now wih he offse included (as displayed on he righ side of Figure 5). I coil No microsep a he zero curren crossing! No microsep a he zero curren crossing! Figure 6. Half Sepping wih Offse Table 1 on page 7 can be used o know a which Microsep Posiion (see Saus Regiser 3 of AMIS 305xx) he sepping mode may be changed wihou creaing an offse. Changing o a higher resoluion can be done a any momen. Changing o a lower resoluion may only be done if he Microsep Posiion is also presen in he lower sepping mode. More info on Table 1 can be found in he SLA Check secion. 3

4 Below oscilloscope plos display he coil currens and he SLA volage measured a 1/8 microsepping. In he firs plo (Figure 7) no offse is creaed resuling in a microsep posiion on he coil curren zero crossing. The volage measured on he SLA pin will represen he real Bemf volage of he sepper moor. In he second plo (Figure 8) an offse is creaed. No microsep posiion is locaed on he coil curren zero crossing. The volage measured on he SLA pin will no represen he real Bemf volage of he sepper moor. X coil Y coil V SLA X coil Coil curren zero crossing Y coil Microsep posiion is locaed a he zero curren crossing (= full sep posiion). The measured SLA volage (V SLA ) will be a correc represenaion of he Bemf volage. V SLA Figure 7. Oscilloscope Plo of 1/8 Microsepping wih Microsep Posiion Locaed a he Zero Curren Crossing 4

5 X coil V SLA Coil curren zero crossing X coil Y coil Because here is an offse creaed, no microsep posiion is locaed a he zero curren crossing (= full sep posiion). The measured SLA volage (V SLA ) will no represen he real Bemf volage. V SLA Figure 8. Oscilloscope Plo of 1/8 Microsepping wih No Microsep Posiion Locaed a he Zero Curren Crossing 5

6 SLA Check Alhough he microconroller conrols he sepper moor driver, i s always possible ha an offse is creaed unwonedly. By reading ou he Microsep Posiion (Saus Regiser 3) he microconroller can check if an offse is creaed or no. Table 1 displays all possible Microsep Posiions for all sepping modes excep full sep. If a any momen he read ou Microsep Posiion is equal o a value given in his able (for a cerain sepping mode), no offse is creaed (see also Figure 9). If anoher value is read ou, an offse is creaed and no microsep posiion will be locaed on he coil curren zero crossing (see also Figure 10). The SLA volage will no represen he real Bemf of he sepper moor Figure 9. Possible Microsepping Posiions for Correc Bemf Measuremen (1/8 Microsepping) Figure 10. Example of 1/8 Microsepping wih Offse 6

7 Table 1. MICROSTEP POSITIONS FOR DIFFERENT STEPPING MODES (no offse) Sepping Mode Sepping Mode Sepping Mode 1/32 1/16 1/8 1/4 1/2 1/32 1/16 1/8 1/4 1/2 1/32 1/16 1/8 1/4 1/

8 Transparency Mode I s no 100% correc o say ha he volage on he SLA pin will represen he real Bemf volage of he sepper moor if a microsep posiion is locaed a he coil curren zero crossing. A he momen he curren less sae is enered, he coil volage is measured. Because a ha momen he coil curren will no ye be zero (i akes ime o ge all he curren ou of he coil), he coil volage will clamp o he power supply volage (VBB) V. Once he coil curren is zero, he coil volage will decay (ransien behavior). The coil volage will decay o he Bemf volage of he sepper moor. I s only a ha momen ha he coil volage will be equal o he Bemf volage of he moor! I coil Previous Microsep Coil Curren Zero Crossing Nex Microsep I coil Nex sep Curren Decay Nex sep V coil V BB +0.6V Volage Transien V BEMF Figure 11. Coil Volage Behavior During Curren Less Sae If he speed of he sepper moor is se oo high, i s possible ha he nex (micro)sep is se before he ransien behavior has ended. If his is he case, he volage on he SLA pin will never represen he real Bemf volage. To help deermining if his is he case, AMIS 305xx has a so called ransparen mode. In his mode he coil volage during he curren less sae can be measured on he SLA pin. This makes i possible o monior he ransien behavior of he coil volage during his sage and o verify if he real Bemf volage of he sepper moor can be sampled. 8

9 When working in ransparen mode, he SLA volage will be updaed a he rae of he PWM frequency when he moor is locaed in he coil curren zero crossing. The ransien behavior can be moniored. As can be seen in Figure 12, he ransien behavior has ended before he nex (micro)sep is se. The real Bemf volage of he sepper moor can be measured. Verifying he ransien behavior of he coil volage during he curren less sae is only done during developmen (for mos applicaions). In he final applicaion i s no needed o sample his complee ransien behavior. For his AMIS 305xx has a so called no ransparen mode. In his mode he coil volage is also sampled a he PWM rae when he coil curren is zero bu he volage on he SLA pin is only updaed from he momen he coil curren zero crossing sae is lef (see also Figure 12). The ransien behavior will no be seen by he microconroller (which is also no needed for mos applicaions). Keep in mind ha he SLA volage is only updaed when leaving he curren less sae. The SLA volage measured during he curren less sae will acually represen he Bemf volage of he previous full sep. 9

10 I coil Previous Microsep Coil Curren Zero Crossing Nex Microsep I coil Nex sep Curren Decay Nex sep PWM Rae V coil V BB +0.6V V BEMF V SLA Transparen Mode Transien behavior Las sample before leaving zero crossing is reained. V SLA No Transparen Mode Bemf of previous zero crossing. SLA volage is only updaed afer curren less sae is lef+ a cerain delay (50us a room emp). Figure 12. Volage Measured on he Coil and SLA pin for No Transparen Mode 10

11 Maximum Operaing Speed As explained in Transparency Mode, one needs o be careful when o measure he BEMF. Afer he sar of he coil curren zero crossing i akes some ime before he real BEMF can be measured (see Figure 11). Leaving he coil curren zero crossing sage oo early will resul in an incorrec BEMF sampling (= he measured volage on he SLA pin will no represen he real BEMF). This will limi he maximum operaing speed. The maximum operaing speed will depend on nex parameers: Sepper moor Coil curren Operaing volage Sepping mode I s bes o choose a sepper moor wih low series resisance (few Ohms or less). For high speed applicaions i will also be imporan o choose a sepper moor wih low inducance. The coil curren has o be defined in such a way ha enough orque is produced by he sepper moor o roae he load wihou loosing seps. For silen operaion, a high sepping mode is advised. Bu as will be seen laer, his will limi he maximum roaion speed. The operaing volage will depend on he used moor, operaing speed and coil curren. I s imporan o operae he sepper moor wihin his operaing range. Finding he maximum operaing speed can bes be done by measuring. For his he AMIS 3052x Evaluaion Ki can be used. This Evaluaion Ki can be ordered from he ON Semiconducor websie ( Below seps explain how o deermine he maximum operaing speed by using he AMIS 3052x EVK. Sep 1: Remove capacior C3 from he AMIS 3052x Moherboard (schemaics and layou can be found in he Graphical User Inerface). This capacior will filer he SLA signal. Alhough i s advised o add his capacior in he final applicaion, his capacior will influence our measuremen and should be removed. Sep 2: Build he Evaluaion Ki seup (see documenaion provided wih he Evaluaion Ki). Make sure ha he correc operaing volage is used (connec your own power supply if needed) and ha he correc sepper moor is used. Sep 3: Do no connec any signal o he NXT pin! Sep 4: Press he CLR pin one ime o clear he digial. Sep 5: Sep 6: Sep 7: Sep 8: Sep 9: Se he Coil Curren and Sepping Mode (Conrol Regiser 0). Se SLA Transparency o Transparen and enable he moor driver (Conrol Regiser 2). Connec he NXT signal. Se he NXT frequency very low. Roor should be roaing very slowly resuling in no BEMF. Verify if here is no offse creaed by reading he Microsepping Posiion (Saus Regiser 3). This can easily be done by enabling Check SLA Oupu in he Graphical User Inerface (GUI) of he AMIS 3052x Evaluaion Ki (see Figure 13). When checked, he Microsepping Posiion will color red if an offse is creaed (when Saus Regiser 3 is read ou). Figure 13. Check SLA Oupu If he Microsepping Posiion colors red afer reading ou SR3, go back o Sep 1! Measure he coil curren in one of he coils, measure he volage on he SLA pin and monior he NXT pin. Bes is o rigger he oscilloscope on he coil curren zero crossing. Figure 14 gives he resuls measured wih a Nidec Servo sepper moor operaed a 12 V and 415 ma coil curren. Sepping mode was se o 1/8 microsepping. A zoom is aken on he coil curren zero crossing. A he rising edge of he NXT signal (purple curve) he coil curren will be regulaed o zero. Noice ha he SLA volage (yellow curve) claps o 5 V. This is because he coil volage (no visible on he oscilloscope plo) will clamp o Vba V (see Figure 11). Afer his you see he SLA volage drop o zero. This is he ransien par (see Figure 11). Keep in mind ha he SLA volage is only updae a he PWM frequency rae (his gives he seps in he SLA volage). 11

12 155us Laes noiceable sep in SLA volage (SLA volage approx. 0V). Figure 14. Define Maximum Operaing Speed The ime measured beween he rising edge of he NXT signal (purple curve) and he laes noiceable sep in he SLA volage (yellow curve) will define he maximum operaing speed. As can be seen in Figure 14 his ime is abou 155 s. Knowing ha he sepping mode aken is 1/8 microsepping and ha he coil curren zero crossing should a leas ake 155 s, he maximum NXT frequency is: Hz (eq. 1) 155 s This will resul in a velociy of: 6450 Hz 806 FS (eq. 2) 8 sec Figure 15 displays he resul a 800 FS/sec (close o he maximum speed). The measured SLA volage a his speed will sill represen he real BEMF (measured a he end of he zero crossing). 12

13 Figure 15. SLA Volage a 800 Full Seps / sec Noice he sable SLA volage in Figure 16 when he SLA Transparency is se o No Transparen (Conrol Regiser 2). In No Transparen he clamping and ransien behavior is removed from he SLA signal giving a beer view on he BEMF (see also Figure 12). 13

14 Figure 16. SLA Volage a Maximum Speed in No Transparen Mode Noice in Figure 16 ha he measured SLA volage is abou 2.5 V. If he measured volage would be clamped o 5 V i s possible ha he generaed BEMF is oo high. Se he SLA Gain o 1/4 (Conrol Regiser 2). When he NXT frequency is increased o 7 khz (875 FS/sec), he BEMF is someimes sampled oo fas resuling in an incorrec SLA volage (see Figure 17). The jumps in he SLA volage is because he coil curren zero crossing is lef oo early and he ransien par is sampled (see also Figure 11). 14

15 Figure 17. Too High Speed Resuls in Incorrec BEMF Sampling If he maximum operaing speed is lower han he required operaing speed, some of he applicaion parameers need o be changed o increase he maximum operaing speed. Nex are some possible adjusmens ha could be done. Choose sepper moor wih lower series resisance Choose sepper moor wih lower inducance. Keep in mind ha his will have an effec on he orque! Increase he operaing volage Choose a lower coil curren. Keep in mind ha his will resul in a lower orque. Choose a lower sepping mode (1/4 insead of 1/8 for insance). This will resul in longer coil curren zero crossings. A rick o increase he maximum operaing speed wihou he need of changing any of he above parameers is by sreching he coil curren zero crossing. This principle is also used in AMIS 3062x (see and is called MinSamples. See Applicaion Noe AND8371/D for more info on his. 15

16 Full Sep Sepping Mode All explanaion given above is only valid if he sepping mode is no se o full sep. This is because afer a hard rese of he moor driver, full sep mode will always sar from a half sep posiion meaning ha no microsep posiion will be locaed on he coil curren zero crossing (see also Figure 1). Creaing an offse on purpose o move he sep posiions o a coil curren zero crossing will no be possible making Bemf measuremen in his sepping mode impossible. There is however a possibiliy o operae he sepper moor in full sep mode and measure he Bemf volage. Follow nex seps o operae he sepper moor in full sep mode by using AMIS 305xx half sep sepping mode seing. 1. Rese moor driver 2. Se coil curren. Se he sepping mode o compensaed half sep. 3. Enable he moor driver (sepper moor should be locaed in a full sep posiion) 4. Every ime a full sep has o be se, apply wo NXT pulses fas afer each oher (keeping NXT pin limiaions in mind). In he nex figure one can see ha he sepper moor is running in full sep mode alhough he sepping mode of AMIS 305xx is se o compensaed half sep. Because of he relaive high inducance of he moor, he very shor ime beween he wo NXT pulses (see zoomed par of Figure 18) and he inernal delay of he driver, he half sep posiion will never be reached on ime. The sepper moor will run in full sep mode. 16

17 Y coil X coil V SLA V NXT Y coil The curren rise and fall ime are oo high o reach he half sep posiion. The sepper moor will run in full sep. X coil V SLA V NXT Apply wo NXT pulses fas afer each oher. Figure 18. Operaing Sepper Moor in Full Sep by Using Half Sep Sepping Mode 17

18 High Temperaure When operaing he sepper moor driver a high emperaure i is possible ha he SLA volage drops beween wo samples aken. This could creae unwaned resuls. For his reason i s imporan o measure he SLA volage as fas as possible afer i has been updaed. Nex oscilloscope plo displays he problem. Coil curren zero crossing Beween wo SLA measuremens (= full sep posiions), he SLA volage drops because of he high IC emperaure. Sampling he SLA volage oo lae could resul in an incorrec Bemf volage inerpreaion. Figure 19. Decrease of SLA volage a High Temperaure As can be seen, he SLA volage drops beween wo full sep posiions. If he SLA volage is sampled oo lae by he microconroller or DSP, an incorrec Bemf volage inerpreaion will occur. If he SLA volage is sampled righ afer i has been updaed, he emperaure effec will have a minimum influence on he resul. Good PCB design can reduce he drop of he SLA volage. If a large enough PCB hea sink is foreseen or an addiional head sink is used o ge he hea ou of he package, he die emperaure will drop and he drop in SLA volage will reduce. 18

19 Sample The SLA Volage Figure 20 gives a ypical applicaion schemaic. V DD 100 nf 100 nf 100 nf + D1 V BAT C nf R 2 R 3 C 4 C 2 C 3 C6 VDD VBB VBB VCP C nf 100 F C C 8 R 1 DIR NXT DO DI CLK CS CLR ERR SLA CPN C nf CPP MOTXP 25,26 AMIS 30521/ NCV ,22 MOTXN 13 M MOTYP 12 15,16 6 MOTYN 19,20 7 1, HV , 18 23, TSTO GND Figure 20. Typical Applicaion Schemaic Sampling of he SLA volage is done by he microconroller ADC. Because he BEMF can only be sampled once per full sep, i s no needed o have a high sampling rae. The ADC resoluion depends on how accurae one wans o measure he SLA volage 3. As explained in Transparency Mode, he SLA volage is only updaed afer he coil curren zero crossing is lef (No Transparen Mode). Keep his in mind when sampling he SLA volage. Also, he low pass filer (R1 and C8) will inroduce a delay in he measured signal. Because he SLA volage is updaed a he PWM Frequency rae in Transparen Mode, one could already measure he BEMF during he coil curren zero crossing. If one knows how long he clamping and ransien pars lass (defined in secion Maximum operaing Speed), he microconroller can sample he SLA volage righ afer his ransien par. Or o make i even simpler, he microconroller could sample he SLA volage a he momen he nex microsep is given by he microconroller. No need o inroduce an addiional delay 4 as would be he case when working in No Transparen mode (see Figure 21). When working in Transparen mode, he ransien behavior will be presen on he SLA pin. The microconroller should jus ignore his. 3. The coil volage is sampled by a Sample and Hold circui. There is no digial conversion done by AMIS 305xx. 4. If he sepper moor is operaed close o he maximum operaing speed i s advised o inroduce a delay beween he NXT pulse and sampling of he SLA volage. 19

20 I coil Previous Microsep Coil Curren Zero Crossing Nex Microsep I coil Nex sep Nex sep V coil V BB +0.6V V BEMF V SLA Transparen Mode Earlies momen o sample Easies momen o sample is a nex sep. V SLA No Transparen Mode Earlies momen o sample in No Transparen Figure 21. Difference Beween Transparen and No Transparen Mode 20

21 Examples Below some examples are given on how o use he SLA pin. The flowchar given in hese examples represen he microconroller firmware (see Figure 20). All examples and flowchars given in his documen are solely inended o simplify he explanaion and o help you beer undersand how o use he SLA pin. Drive Moor Figure 22 displays a simple way of driving a sepper moor. In his example he SLA pin is no used ye. The momen he applicaion is powered, he microconroller will be iniialized. When his is done, he coil curren and sepping mode will be se. The moor driver will be enabled and NXT pulses will be send o roae he moor. The imer will deermine he ime beween NXT pulses and by his deermine he roaion speed. In heory he sepper moor should be acceleraed o he maximum speed bu his is ou of he scope of his documen. We assume he speed is low enough o sar wihou acceleraion. The roaion speed mus also be lower han he maximum operaing speed (see Secion Maximum operaing Speed). Power Up Iniialize microconroller Se Coil Curren Se Sepping Mode Conrol Regiser 0 Enable Moor Conrol Regiser 2 Send NXT Pulse Sar Timer Timer Overflow? N Y Figure 22. Simple Moor Conrol Example Above flowchar is a very simple example of driving a sepper moor. No diagnosics is done, no verificaion if sepper moor is roaing,... The only inenion of his example is o roae he moor wih a minimum of overhead. Driving a sepper moor in real life applicaions will be more complex bu is ou of he scope of his documen. Every ime a NXT pulse is send he microconroller will check if he coil curren zero crossing phase is lef. If so, he microconroller knows he SLA volage will be updaed and will sample he SLA pin. An addiional delay is added before sampling he SLA pin (inernal updae delay of moor driver, see Transparency Mode). Sample SLA The flowchar in Figure 23 gives he momen when o sample he SLA volage when working in 1/8 microsepping. 21

22 Power Up Iniialize microconroller Se Coil Curren Se Sepping Mode Enable Moor Send NXT Pulse Sar Timer Read Microsep Posiion Saus Regiser 3 If MSP = (4 OR 36 OR 68 or 100) N Y Values only valid for 1/8 micro sepping See Table 1 for oher sepping modes Delay Sample SLA pin Timer Overflow? N Y Figure 23. Sample SLA volage (1/8 microsepping) The disadvanage of above flowchar is he need o read ou he Microsep Posiion. Because his akes ime (SPI communicaion), his will limi he maximum operaing speed. If needed he microconroller could implemen his own posiioner o keep rack. This would eliminae he needed SPI communicaion. This is however ou of he scope of his documen. Above flowchar can be used when ransparency mode is se o No Transparen or Transparen. However, if Transparen is used he delay before sampling of he SLA pin can be removed. If Transparen mode is chosen, he SLA pin could already be sampled during he coil curren zero crossing. This is given in Figure 24. When he coil curren zero crossing is enered, he SLA pin will be sampled. A delay is added before sampling. In his case his delay is needed o make sure he clamping and ransien phase are ended and he real BEMF is sampled (see also Figures 11 and 21). 22

23 Power Up Iniialize microconroller Se Coil Curren Se Sepping Mode Enable Moor Driver Transparen Mode Send NXT Pulse Sar Timer Read Microsep Posiion If MSP = (0 OR 32 OR 64 OR 96) Y N Delay Sample SLA pin Timer Overflow? N Y Figure 24. Sample SLA volage in Transparen Mode Sall Deecion The flowchar in Figure 25 gives a simple implemenaion of sall deecion (based on Figure 24). The sampled SLA volage will be compared o a hreshold value. If he sampled SLA volage is below he hreshold, moion will be sopped. The hreshold has o be se in such a way ha he sampled SLA volage is higher han he hreshold when he moor is free running. If he moor ges blocked, he BEMF will drop and by his also he SLA volage resuling in a sall deeced. Moion will be sopped. Implemening he flowchar as given in Figure 25 will mos probably fail. This because he SLA volage is already sampled a he firs coil curren zero crossing. During sar of he roaion oscillaions will be seen in he BEMF (acceleraion of he roor) and by his also in he SLA volage. I s possible ha hese oscillaions rigger he sall deecion alhough no sall is presen. I s bes o skip he sall deecion for he firs full seps. This is however ou of he scope of his documen. 23

24 Power Up Iniialize microconroller Se Coil Curren Se Sepping Mode Enable Moor Transparen Mode Send NXT Pulse Sar Timer Read Microsep Posiion If MSP = (0 OR 32 OR 64 OR 96) Y N Delay Sample SLA pin SLA below Threshold? Y N Sop Timer Overflow? N Y Figure 25. Simple Sall Deecion SLA Check Wih he flowchar given in Figure 25 we are able o sample he SLA volage in a correc way and o perform simple sall deecion. The only issue ha could occur is an offse. If for some reason an offse is creaed, no microsep will be locaed anymore on he coil curren zero crossing. The SLA volage can no be sampled nor can sall deecion be done. Figure 26 gives a simple soluion o his problem. If an offse is deeced, moion is sopped. In a real life applicaion he microconroller could do correcive acions or repor he problem. This is ou of he scope of his documen. 24

25 Power Up Iniialize microconroller Se Coil Curren Se Sepping Mode Enable Moor Transparen Mode Send NXT Pulse Sar Timer Read Microsep Posiion MSP = Microsep Posiion MOD = Remainder of a division Y = 2 for 1/16 microsepping, 4 for 1/8 microsepping 8 for 1/4 microsepping and 16 for half sepping If MSP = (0 OR 32 OR 64 OR 96) N Y Delay If MSP MOD Y = 0 Sample SLA pin SLA below Threshold? Y N Timer Overflow? N Y Sop Figure 26. SLA Check 25

26 By sampling he SLA pin as given in Figure 26, one samples he SLA pin a he correc momen o make sure ha he real BEMF is measured. An offse will be deeced as well as a sall condiion. By sampling he SLA pin a he righ momen, emperaure effec will be eliminaed (see High Temperaure). Microconroller wihou ADC To implemen above flowchars one needs o use a microconroller wih ADC. In some cases his ADC is no available. A simple way o enable sall deecion in his case is by using a comparaor. Vdd Vcc Vdd R pull up R 1 Micro Conroller IO COMP SLA AMIS 305xx GND R 3 GND R 2 Figure 27. Sall Deecion wih Comparaor R1 and R2 se he hreshold level. R3 adds a hyseresis o avoid oggling caused by noise. The microconroller can check if he SLA volage is above or below he hreshold level by monioring he digial IO pin. The way o implemen sall deecion says similar. The only difference wih he flowchar in Figure 26 is ha insead of sampling he SLA volage wih an ADC, he saus of he IO pin is checked o deermine if SLA volage is above or below he hreshold level. The momen he saus of his digial IO is checked says he same. If a variable hreshold is needed, R1 and R2 can be replaced by a poeniomeer or even by a digial poeniomeer conrolled by he microconroller (see for Digial Programmable Poeniomeers and Comparaors). R3 is no mandaory bu is advised o avoid oggling cause by noise on he SLA pin. If R3 is no used, a low pass filer should be added o he SLA pin (see also Figure 20). Working wih a digial IO can also be beneficial o offload he CPU of he microconroller. Sampling an analog value could ake some ime. Monioring a digial pin gives low CPU load. Conclusion Implemening he bes sall, seploss or orque adapive algorihm is useless if he SLA pin of AMIS 305xx is no used properly. By following some simple guidelines, he SLA pin can be used in a correc and reliable way. References Ref 1: AMIS 305xx daashee ( Company or Produc Inquiries For more informaion abou ON Semiconducor s producs or services visi our Web sie a hp:// ON Semiconducor and are regisered rademarks of Semiconducor Componens Indusries, LLC (SCILLC). SCILLC reserves he righ o make changes wihou furher noice o any producs herein. SCILLC makes no warrany, represenaion or guaranee regarding he suiabiliy of is producs for any paricular purpose, nor does SCILLC assume any liabiliy arising ou of he applicaion or use of any produc or circui, and specifically disclaims any and all liabiliy, including wihou limiaion special, consequenial or incidenal damages. Typical parameers which may be provided in SCILLC daa shees and/or specificaions can and do vary in differen applicaions and acual performance may vary over ime. All operaing parameers, including Typicals mus be validaed for each cusomer applicaion by cusomer s echnical expers. SCILLC does no convey any license under is paen righs nor he righs of ohers. SCILLC producs are no designed, inended, or auhorized for use as componens in sysems inended for surgical implan ino he body, or oher applicaions inended o suppor or susain life, or for any oher applicaion in which he failure of he SCILLC produc could creae a siuaion where personal injury or deah may occur. Should Buyer purchase or use SCILLC producs for any such uninended or unauhorized applicaion, Buyer shall indemnify and hold SCILLC and is officers, employees, subsidiaries, affiliaes, and disribuors harmless agains all claims, coss, damages, and expenses, and reasonable aorney fees arising ou of, direcly or indirecly, any claim of personal injury or deah associaed wih such uninended or unauhorized use, even if such claim alleges ha SCILLC was negligen regarding he design or manufacure of he par. SCILLC is an Equal Opporuniy/Affirmaive Acion Employer. This lieraure is subjec o all applicable copyrigh laws and is no for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Lieraure Disribuion Cener for ON Semiconducor P.O. Box 5163, Denver, Colorado USA Phone: or Toll Free USA/Canada Fax: or Toll Free USA/Canada orderli@onsemi.com N. American Technical Suppor: Toll Free USA/Canada Europe, Middle Eas and Africa Technical Suppor: Phone: Japan Cusomer Focus Cener Phone: ON Semiconducor Websie: Order Lieraure: hp:// For addiional informaion, please conac your local Sales Represenaive AND8399/D