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july 2014 docid15255 rev 2 1/29 29 AN2859 application note multiplexed diagnostics of ac switches using two stcc08 introduction the aim of this application note is to present opportunities to reduce the number of input pins used on a microcontroller unit (mcu) to diagnose failures of several ac switches with the stcc08. this document deals with the multiplexed diagnostics of two stcc08 and gives technical recommendations on the implementation of this solution. stcc08 overview the stcc08 has been designed to improve home appliance safety. this new device can drive an ac switch (triac, acst and acs) with a gate current i gt up to 10 ma and to send back to the microcontroller unit a signal image of the voltage across the controlled ac switch (this signal defines the ac switch state). the stcc08 has three functional blocks (see figure 1 ). ? a "gate driver" block used to drive an ac switch and to interface directly the stcc08 with the mcu (cmos compatible) ? a "power switch signal shaping" block used to measure the ac switch voltage in both ac line cycles ? an "avf driver" block used to give an image of the ac switch voltage to the mcu (digital information) figure 1. stcc08 block diagram for more information about the stcc08, please refer to the st application note an2716. avf v cc gnd r ig ac in g power switch signal shaping avf driver gate driver + - avf gnd stcc08 stcc08 ac r ig g avf in gnd v cc n/c so -8 1 2 3 4 8 5 6 7 www.st.com
contents AN2859 2/29 docid15255 rev 2 contents 1 multiplexed diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 failure mode detection of two ac switches . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 v avf signal reading synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2v state level definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3 resistance settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4 detection windows digital value setting . . . . . . . . . . . . . . . . . . . . . . . . 15 5 application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6 conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 appendix a ac switch state deduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 appendix b v state signal voltage definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 appendix c resistor settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 c.1 first case: v 1_min > v 0_max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 c.2 second case: v 2_min > v 1_max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 c.3 third case: v 2_max < v 3_min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
docid15255 rev 2 3/29 AN2859 multiplexed diagnostics 29 1 multiplexed diagnostics 1.1 principle the multiplexed diagnostic allows the detection of the state of several ac switches independently using only one mcu input. in this case, an analog/digital converter input (adc) of the mcu should be used and must be configured with no pull-up resistor. in this document, only the multiplexed diagnostic of two stcc08 (stcc08 1 and stcc08 2 ) is described (see figure 2 ). note that two output pins of an mcu should be used to control each stcc08 (in1 and in2). figure 2. multiplexed diagnostic schematic of two stcc08 to distinguish the state of each ac switch (acs1 and acs2) a divider bridge is used. resistors r 1 , r 2 , r 3 and r 4 are designed to convert the v avf digital signal given by each stcc08 (v avf1 and v avf2 ) into an analog signal (v state ). knowing the control state of each stcc08 (in1 and in2), the mcu is able to identify the state of each ac switch by analyzing the v state signal (see section 1.2 ). note: the stcc08 avf output is an open collector output. resistors r 1 and r 3 bias the stcc08 avf output and limit the collector current to 5 ma. for further information, and in particular, resistor values for r ac , r shunt , and r ig , refer to the st application note an2716. avf r ig ac in2 g mcu avf load2 line neutral acs2 stcc08 2 avf v cc gnd r ig ac in1 g avf gnd load1 line neutral acs1 v cc v cc r1 r2 r3 r4 v state v avf2 v avf1 stcc08 1 r ac r ac r shunt r shunt v cc v cc
multiplexed diagnostics AN2859 4/29 docid15255 rev 2 1.2 failure mode detection of two ac switches figure 3 to figure 12 give the v state signal level according to the state of each ac switch. v 0 , v 1 , v 2 and v 3 are levels reached by the parameter v state and depends on r1, r2, r3, and r4 resitor values. table 1 shows that we only need four different levels to define the state of each ac switch. figure 3. case 1: v state = v 3 (except at each zero crossing of the ac line) figure 4. case 2: v state = v 0 vcc vcc r1 r2 r3 r4 v state v3 v2 v1 v0 vstate stcc08 2 v avf2 v avf1 avf avf v ac i load_1 v ac i load_2 ac ac stcc08 1 vcc/com rac vcc/com acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt in2 in1 g g v ac v ac acs1 and acs2 are not in conducting state v2 v1 v0 i load_1 i load_2 vcc vcc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac vcc/com rac vcc/com acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac vstate stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 and acs2 are in conducting state
docid15255 rev 2 5/29 AN2859 multiplexed diagnostics 29 figure 5. case 3: v state = v 1 (except at each zero crossing of the ac line) figure 6. case 4: v state = v 2 (except at each zero crossing of the ac line) v2 v1 v0 i load_1 i load_2 v cc v cc r1 r2 r3 r4 v avf2 v avf1 avf avf ac ac rac vcc/com acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac vstate stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 is in conducting state and acs2 is not in conducting state v /com cc v state v2 v1 v0 i load_1 i load_2 v cc vcc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 is not in conducting state and acs2 is in conducting state
multiplexed diagnostics AN2859 6/29 docid15255 rev 2 figure 7. case 5: v state toggles between v 1 and v 3 at each ac line cycle (except at each zero crossing of the ac line) figure 8. case 6: v state toggles between v 2 and v 3 at each ac line cycle (except at each zero crossing of the ac line) v2 v1 v0 i load_1 i load_2 v cc v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 is failed in diode mode and acs2 is not in conducting state v2 v1 v0 i load_1 i load_2 v ac v ac v cc v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 is not in conducting state and acs2 is failed in diode mode
docid15255 rev 2 7/29 AN2859 multiplexed diagnostics 29 figure 9. case 7: v state toggles between v 1 and v 2 at each ac line cycle (except at each zero crossing of the ac line) figure 10. case 8: v state toggles between v 0 and v 3 at each ac line cycle (except at each zero crossing of the ac line) v cc v2 v1 v0 i load_1 i load_2 v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 and acs2 are failed in diode mode not on the same ac line polarities v2 v1 v0 i load_1 i load_2 v cc v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac acs1 and acs2 are failed in diode mode on the same ac line polarities
multiplexed diagnostics AN2859 8/29 docid15255 rev 2 figure 11. case 9: v state toggles between v 2 and v 0 at each ac line cycle figure 12. case 10: v state toggles between v1 and v0 at each ac line cycle acs1 is failed in diode mode and acs2 is failed in short circuit v cc v2 v1 v0 i load_1 i load_2 v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac v /com cc rac v /com cc acs2 acs1 load1 line load2 line i load_2 i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v ac v ac v2 v1 v0 i load_1 i load_2 v cc v cc r1 r2 r3 r4 v state v avf2 v avf1 avf avf ac ac rac v /com cc acs2 acs1 load1 line load2 line i load_1 rshunt rac rshunt v ac v ac v state stcc08 2 stcc08 1 v3 in2 in1 g g v /com cc i load_2 v ac v ac acs1 is failed in shot circuit and acs2 is failed in diode mode
docid15255 rev 2 9/29 AN2859 multiplexed diagnostics 29 knowing the control state of each stcc08 (in1 and in2) and according to ta ble 1 , the mcu is able to detect the ac switch state by analyzing v state signal. appendix a defines the states of each acs according to the v state signal level (v 0 , v 1 , v 2 and v 3 ) and the control state of each stcc08. in the case of failure of one of the ac switches, the mcu can place the application in a safe configuration by switching off an appliance front-end relay. 1.3 v avf signal reading synchronization the stcc08 avf output signal is an image of the ac switch voltage. this signal toggles between v cc and zero level (gnd) according to whether the stcc08 ac input current (i ac ) is higher or not than i act (see an2716). in case of multiplexed diagnostics the slight i act electrical variation between ics may result in the state of the avf signal of each stcc08 (either v cc or zero level) not changing at exactly the same time. this has an impact on the v state signal and on the ac switches state detection (see figure 13 ). note that i act1 and i act2 define respectively the sttco8 i ac input current for stcc08 1 and stcc08 2 to allow v avf signal to toggle between vcc and gnd. for example, if the two stcc08 are not controlled (in1 = in2 = 0) and ac1 and ac2 are not in conducting state the ac1 and ac2 can be interpreted (see tab le 1 ) as failed in short circuit if v state is read between t 0 and t 1 (v state = v 0 ). table 1. variation of the v state signal according to the ac switch states acs1 state acs2 state v state status on on v state = v 0 on off v state = v 1 off on v state = v 2 off off v state = v 3
multiplexed diagnostics AN2859 10/29 docid15255 rev 2 figure 13. v state signal variation due to the i act parameter dispersion note: it is recommended that the avf signal be read during several ac line cycles around the ac line peak voltage. the stcc08 avf signal must be read after the ac line peak voltage ( t avf_read ) and before the t3 (see an2716). v line i= ac1 i ac2 avf1 (stcc08_1) i act2 -i act2 t (s) t (s) ? t 1 t = 0 0 2 x f 1 avf2 (stcc08_2) t (s) v state t (s) i act1 -i act1 t 2 t 3 t 4 t = 5 v cc v cc v 1 v 3 t detection t avf_read
docid15255 rev 2 11/29 AN2859 v state level definition 29 2 v state level definition according to the state of each ac switch, v 0 , v 1 , v 2 and v 3 levels are defined by equations 1 , 2 , 3 and 4 (see also appendix b ). in this document v avf1_l and v avf2_l are respectively the stcco8 1 and stcco8 2 avf output at the low level. the minimum and maximum values of avf at low level are respectively 0 v and 1 v. equation 1 acs1 and acs2 are on equation 2 acs1 is on and acs2 is off equation 3 acs2 is on and acs1 is off equation 4 acs1 and acs2 are off the tolerance of the resistors (r 1 , r 2 , r 3 and r 4 ), the stcc08 output avf signal electrical dispersion and the dc power supply characteristics induce a dispersion on v 0 , v 1 , v 2 and v 3 levels (see ta ble 2 ). knowing the previous equations 1 , 2 , 3 and 4 , the resistors standard value and the tolerance of the resistors, v x_max and v x_min (x = 0, 1, 2, or 3) values are defined respectively by equations 5 , 6 , 7 , 8 , 9 , 10 , 11 and 12 . table 2. variation of the v state signal according to the ac switch states acs1 state acs2 state v state status on on v 0_min < v state < v 0_max on off v 1_min < v state < v 1_max off on v 2_min < v state < v 2_max off off v 3_max > v state > v 3_min () 4 2 4 avf2_l 2 avf1_l 0 r r r v r v v + + = () 4 2 1 2 1 avf1_l 4 cc 1 r r r r r v r v v + + + + = () 4 3 2 4 3 avf2_l 2 cc 2 r r r r r v r v v + + + + = cc 3 v v =
v state level definition AN2859 12/29 docid15255 rev 2 v cc_min and v cc_max are respectively the minimum and maximum power supply voltage of the application. x r_max and x r_min are the tolerances of the resistors. for example, with 5% resistor tolerance x r_max and x r_min are respectively 1.05 and 0.95. v avf_l_max and v avf_l_min values are fixed by the stcc08 avf output electrical dispersion at low level with: v avf_l_max = v avf1_l_max = v avf2_l_max = 1 v and v avf_l_min = v avf1_l_min = v avf2_l_min = 0 v equation 5 asc1 is on and acs2 is on. equation 6 asc1 is on and acs2 is on. equation 7 asc1 is on and acs2 is off. equation 8 asc1 is on and acs2 is off. equation 9 asc1 is off and acs2 is on. r_min r_max avf_l_max r_min 4 2 r_max 4 2 avf_l_max 0_max x x v x r r x r r v v = ? ? ? ? ? ? + ? ? ? ? ? ? + = v 0 x r r x r r v v r_max 4 2 r_min 4 2 avf_l_min 0_min = ? ? ? ? ? ? + ? ? ? ? ? ? + = r_min 4 2 1 r_max 2 1 avf_l_max r_max 4 cc_max 1_max x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = r_max 4 2 1 r_min 2 1 avf_l_min r_min 4 cc_min 1_min x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = r_min 4 3 2 r_max 4 3 avf_l_max r_max 2 cc_max 2_max x r r r x r r v .x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + =
docid15255 rev 2 13/29 AN2859 v state level definition 29 equation 10 asc1 is off and acs2 is on. equation 11 asc1 is off and acs2 is off. equation 12 asc1 is off and acs2 is off. r_max 4 3 2 r_min 4 3 avf_l_min r_min 2 cc_min 2_min x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = cc_max 3_max v v = cc_min 3_min v v =
resistance settings AN2859 14/29 docid15255 rev 2 3 resistance settings equation 13 shows how to select values for r 1 and r 3 resistances. i avf_max is the maximum current sunk by the stcc08 avf pin and should be lower than 5 ma. equation 13 knowing the r 1 and r 3 resistor standard values, the tolerance of the resistors, the stcc08 avf output electrical dispersion and the dc power supply characteristic, r 2 and r 4 resistances value should be chosen by using equations 14 , 15 , and 16 (see also appendix c ). equation 14 equation 15 equation 16 avf_max cc_max 3 1 i v 2 r r r = = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + > ? > ? 2 r_min r_max avf_l_max cc_min avf_l_min 2 r_min r_max avf_l_max 2 4 0_max 1_min x x v v v x x v r r r v v ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? < ? > ? avf_l_min 2 r_min r_max cc_max avf_l_min 2 r_min r_max avf_l_max 2 r_min r_max avf_l_max cc_min 2 4 1_max 2_min v x x v v x x v r x x v v r r v v ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? > ? > ? r v x x v x x v v r r v v avf_l_max r_max r_min cc_min r_max r_min cc_min cc_max 2 4 2_max 3_min
docid15255 rev 2 15/29 AN2859 detection windows digital value setting 29 4 detection windows digital value setting to detect the state of both ac switches, an mcu analog/digital converter input (adc) should be used. the conversion result (n adc ) of the v state signal depends on the adc size (n) and of the mcu voltage reference (v ref ). note that the adc transfer function is considered as ideal (see equation 17 ). equation 17 according to the state of the ac switches, the v state signal is not directly dependent on the value of v cc (see equations 1 , 2 and 3 ). this has an impact on the conversion result if the voltage reference of the adc transfer function depends directly on v cc . in this case, the detection levels to implement in the mcu firmware should be determined by taking into account the dc power supply variation with v ref = v cc (see equations 18 , 19 , 20 , 21 , 22 , 23 and 24 ). equation 18 asc1 is on and acs2 is on. equation 19 asc1 is on and acs2 is on. equation 20 asc1 is on and acs2 is off. n ref v state adc 2 v n = ? ? ? ? ? ? ? ? ? ? ? ? ? = ? ? ? ? ? ? + ? ? ? ? ? ? + = ? ? ? ? ? ? ? + ? ? ? ? ? ? + = ? n r_min r_max cc_min avf_l_max n r_min 4 2 r_max 4 2 cc_min avf_l_max 0_max n 4 2 4 2 cc avf_l 0 2 x x v v 2 x r r x r r v v n 2 r r r r v v n 0 n 0_min = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? + + = ? r_min 4 2 1 r_max n cc_min 2 1 avf_l_max 4 1_max n 4 2 1 cc 2 1 avf_l cc 4 1 x r r r x 2 v r r v r n 2 r r r v r r v v r n
detection windows digital value setting AN2859 16/29 docid15255 rev 2 equation 21 asc1 is on and acs2 is off. equation 22 asc1 is off and acs2 is on. equation 23 asc1 is off and acs2 is on. equation 24 asc1 is off and acs2 is off. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? + + = ? r_max 4 2 1 r_min n cc_max 2 1 avf_l_min 4 1_min n 4 2 1 cc 2 1 avf_l cc 4 1 x r r r x 2 v r r v r n 2 r r r v r r v v r n () ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? + + = ? + + r_min 4 3 2 r_max n cc_min 4 3 avf_l_max 2 2_max n 4 3 2 cc 4 3 avf_l cc 2 2 x r r r x 2 v r r v r n 2 r r r v r r v v r n ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + + ? ? ? ? ? ? + + = ? r_max 4 3 2 r_min n cc_max 4 3 avf_l_min 2 1_min n 4 3 2 cc 4 3 avf_l cc 2 2 x r r r x 2 v r r v r n 2 r r r v r r v v r n 2_max 3_min 3_max n n n > =
docid15255 rev 2 17/29 AN2859 application example 29 5 application example the first step is to calculate r 1 and r 3 resistor values using equation 13 . the second step is to choose the r 2 and r 4 resistor values to fulfil equations 14 and 15 (see also ta ble 4 ). the third step is to calculate the window detection levels (see table 5 ) according to equations 5 , 6 , 7 , 8 , 9 , 10 , 11 , 18 , 19 , 20 , 21 , 22 , 23 and 24 . the window detection digital levels will be stored in the mcu firmware to distinguish the state of each ac switch. table 3. defined values of the application symbol value unit i avf_max 5ma v cc_min 4.5 v v cc_max 5.5 v v avf_l_min 0v v avf_l_max 1 v n (mcu adc resolution) 10 bits table 4. r 1 , r 2 , r 3 and r 4 resistor values resistor settings standard value (5% tolerance) r 1 = r 3 > 1.1 k 2.2 k r 2 15 k r 4 6.8 k table 5. detection window values windows detection level analog values (volts) equivalent digital values max. min. max. min. v 0 1.105 0 252 0 v 1 2.514 1.154 501 262 v 2 4.214 2.545 802 579 v 3 5.5 4.5 1024 > 802
conclusion AN2859 18/29 docid15255 rev 2 6 conclusion this application note illustrates how designers can diagnose the state of two ac switches with only one single microcontroller adc input. the way to implement this solution in the application and the external resistor choice is described in this document. this solution is used to detect the failure modes of two ac switches and to inform the mcu so that appropriate actions to put the system into a safe state can be taken. this function improves the system safety by detecting "diode mode" in both polarities of the ac mains, "short circuit" and "open circuit" of each ac switch independently. the main benefit of this solution is to reduce the cost of the microcontroller when a platform needs to monitor several ac switches because it requires one less pin.
docid15255 rev 2 19/29 AN2859 ac switch state deduction 29 appendix a ac switch state deduction table 6. ac switch states when in1 = in2 = 0 in1 in2 v state value acs1 diagnostic acs2 diagnostic 00v 0 shorted circuit shorted circuit 00v 1 shorted circuit off 00v 2 off shorted circuit 00v 3 off off 00 toggle between v 3 and v 2 off diode mode 00 toggle between v 3 and v 1 diode mode off 00 toggle between v 3 and v 0 diode mode diode mode 00 toggle between v 2 and v 1 diode mode diode mode 00 toggle between v 2 and v 0 diode mode shorted circuit 00 toggle between v 1 and v 0 shorted circuit diode mode table 7. ac switch states when in1 = 0 and in2 = 1 in1 in2 v state value acs1 diagnostic acs2 diagnostic 01v 0 shorted circuit on 01v 1 shorted circuit open circuit 01v 2 off on 01v 3 off open circuit 01 toggle between v 3 and v 2 off na 01 toggle between v 3 and v 1 diode mode open circuit 01 toggle between v 3 and v 0 diode mode na 01 toggle between v 2 and v 1 diode mode na 01 toggle between v 2 and v 0 diode mode on 01 toggle between v 1 and v 0 shorted circuit na
ac switch state deduction AN2859 20/29 docid15255 rev 2 table 8. ac switch states when in1 = 1 and in2 = 0 in1 in2 v state value acs1 diagnostic acs2 diagnostic 10v 0 on shorted circuited 10v 1 on off 10v 2 open circuit shorted circuited 10v 3 open circuit off 10 toggle between v 3 and v 2 open circuit diode mode 10 toggle between v 3 and v 1 na off 10 toggle between v 3 and v 0 na diode mode 10 toggle between v 2 and v 1 na diode mode 10 toggle between v 2 and v 0 na shorted circuit 10 toggle between v 1 and v 0 on diode mode table 9. ac switch states when in1 = in2 = 1 in1 in2 v state value acs1 diagnostic acs2 diagnostic 11v 0 on on 11v 1 on open circuit 11v 2 open circuit on 11v 3 open circuit open circuit 11 toggle between v 3 and v 2 open circuit na 11 toggle between v 3 and v 1 na open circuit 11 toggle between v 3 and v 0 na na 11 toggle between v 2 and v 1 na na 11 toggle between v 2 and v 0 na on 11 toggle between v 1 and v 0 on na
docid15255 rev 2 21/29 AN2859 v state signal voltage definition 29 appendix b v state signal voltage definition the v state voltage is defined according to the theorem of superposition applied on the linear circuits defined on figures 14 , 15 , 16 and 17 (according to the state of each ac switch). the voltage resulting (v state ) from each source is calculated separately, and the results are added algebraically. the input current of the mcu a/d conversion block (i a/d ) is neglected. figure 14. equivalent circuit acs1 and acs2 are on equation 25 equation 26 equation 27 v cc v cc r1 r2 r3 r4 v avf2_l v avf1_l avf avf v state r1 r2 r4 stcc08 2 stcc08 1 mcu i a/d 0 r3 v avf1_l v cc v cc v avf2_l a / d conversion v state 2 r 4 r 4 r avf2_l v avf1_l v 0 v state v + = = r_min 4 2 r_max 4 2 avf_l_max 0_max x r r x r r v v ? ? ? ? ? ? + ? ? ? ? ? ? + = 0 x r r x r r v v r_max 4 2 r_min 4 2 avf_l_min 0_min = ? ? ? ? ? ? + ? ? ? ? ? ? + =
v state signal voltage definition AN2859 22/29 docid15255 rev 2 figure 15. equivalent circuit acs1 is on and acs2 is off equation 28 equation 29 equation 30 v cc v cc r1 r2 r3 r4 v avf2_h v avf1_l avf avf v state r1 r1 r2 r4 stcc08 2 stcc08 1 mcu i a/d 0 r3 v avf1_l v cc v cc a / d conversion v state avf1_l 4 2 1 2 1 cc 1 2 4 4 1 state v r r r r r v r r r r v v + + + + + + = = r_min 4 2 1 r_max 2 1 avf_l_max r_max 4 cc_max 1_max x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = r_max 4 2 1 r_min 2 1 avf_l_min r_min 4 cc_min 1_min x r r r x r r v .x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + =
docid15255 rev 2 23/29 AN2859 v state signal voltage definition 29 figure 16. equivalent circuit acs2 is on and acs1 is off equation 31 equation 32 equation 33 v cc v cc r1 r2 r3 r4 v avf2_l v avf1_h avf avf v state r1 r2 r4 stcc08 2 stcc08 1 mcu i a/d 0 r3 vcc v cc v avf2_l a / d conversion v state avf2_l 2 4 3 4 3 cc 3 4 2 2 2 state v r r r r r v r r r r v v + + + + + + = = r_min 4 3 2 r_max 4 3 avf_l_max r_max 2 cc_max 2_max x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = r_max 4 3 2 r_min 4 3 avf_l_min r_min 2 cc_min 2_min x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + =
v state signal voltage definition AN2859 24/29 docid15255 rev 2 figure 17. equivalent circuit acs1 and acs2 are off equation 34 equation 35 equation 36 v cc v cc r1 r2 r3 r4 v avf1_h v avf2_h avf avf v state r1 r2 r4 stcc08 2 stcc08 1 mcu ia/d 0 r3 v cc v cc a / d conversion v state cc 4 3 2 1 2 1 cc 4 3 2 1 4 3 cc 3 state v r r r r r r v r r r r r r v v v = + + + + + + + + + = = cc_max 3_max v v = cc_min 3_min v v =
docid15255 rev 2 25/29 AN2859 resistor settings 29 appendix c resistor settings figure 15 , and equations 37 , 38 and 39 define conditions to identify the state of each ac switch. equation 37 equation 38 equation 39 c.1 first case: v 1_min > v 0_max equations 26 and 30 define respectively v 0_max and v 1_min (see appendix a ). to take into account r 1 resistor?s standardized values (see equation 13 ), the resistor?s tolerance (x r ), the stcc08 avf output electrical dispersion and the dc power supply characteristic, the condition on r 2 and r 4 resistors is defined in equation 42 . equation 40 equation 41 equation 42 0_max 1_min v v > 1_max 2_min v v > 3_min 2_max v v < 0_max 1_min v v > avf_l_max r_max 4 2 1 r_min 2 1 avf_l_min r_min 4 cc_min v x r r r x r r v x r v > ? ? ? ? ? ? + + ? ? ? ? ? ? + + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + > r_min r_max avf_l_max cc_min avf_l_min r_min r_max avf_l_max 2 1 4 x x v v v x x v r r r
resistor settings AN2859 26/29 docid15255 rev 2 c.2 second case: v 2_min > v 1_max equations 29 and 33 define respectively v 1_max and v 2_min (see appendix a ). to take into account r 3 resistor?s standardized values, the resistor?s tolerance (x r ), the stcc08 avf output electrical dispersion and the dc power supply characteristic, the condition on r 2 and r 4 resistors is defined by equation 46 . equation 43 equation 44 equation 45 equation 46 1_max 2_min v v > r_max 4 3 2 r_min 4 avf_l_min r_min 2 cc_min 2_min x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = r_min 4 2 1 r_max 2 1 avf_l_max r_max 4 cc_max 1_max x r r r x r r v x r v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + = avf_l_min 2 r_min r_max cc_max avf_l_min 2 r_min r_max avf_l_max 3 2 r_min r_max avf_l_max cc_min 2 4 v x x v v x x v r x x v v r r ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? <
docid15255 rev 2 27/29 AN2859 resistor settings 29 c.3 third case: v 2_max < v 3_min equations 32 and 36 define respectively v 2_max and v 3_min (see appendix a ). to take into account r 3 resistor?s standardized values, the resistors? tolerance (x r ), the stcc08 avf output electrical dispersion and the dc power supply characteristic, the condition on r 2 and r 4 resistors is defined in equation 49 . equation 47 equation 48 equation 49 3_min 2_max v v < cc_min r_min 4 3 2 r_max 4 3 avf_l_max r_max 2 cc_max v x r r r x r r v x r v < ? ? ? ? ? ? + + ? ? ? ? ? ? + + 3 avf_l_max r_max r_min cc_min r_max r_min cc_min cc_max 2 4 r v x x v x x v v r r ? ? ? ? ? ? ? ? ? ? ? >
revision history AN2859 28/29 docid15255 rev 2 revision history table 10. document revision history date revision changes 08-dec-2009 1 initial release. 29-jul-2014 2 updated figure 13 and the note below it.
docid15255 rev 2 29/29 AN2859 29 important notice ? please read carefully stmicroelectronics nv and its subsidiaries (?st?) reserve the right to make changes, corrections, enhancements, modifications, and improvements to st products and/or to this document at any time without notice. purchasers should obtain the latest relevant in formation on st products before placing orders. st products are sold pursuant to st?s terms and conditions of sale in place at the time of o rder acknowledgement. purchasers are solely responsible for the choice, selection, and use of st products and st assumes no liability for application assistance or the design of purchasers? products. no license, express or implied, to any intellectual property right is granted by st herein. resale of st products with provisions different from the information set forth herein shall void any warranty granted by st for such product. st and the st logo are trademarks of st. all other product or service names are the property of their respective owners. information in this document supersedes and replaces information previously supplied in any prior versions of this document. ? 2014 stmicroelectronics ? all rights reserved

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