Application Note P R O F E T TM + C U R R E N T SENSE What the designer should know Application Note Smart High Side Switches Rev 1.1, 2014-03-14 Body Power App. Note 1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 3.1 3.1.1 3.1.2 3.1.3 3.2 3.2.1 3.2.2 3.2.3 States to Diagnose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagnosis at OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open Load at OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short Circuit to Battery at OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nominal Load / Short to Ground at OFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Detection in ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short to Ground at ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short to Battery at ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Open Load / Partial Loss / Overload at ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1 4.2 4.3 4.4 4.5 4.6 PROFET™+ Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 kILIS and Current Sense representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Power Losses in the Sense Resistor RIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Applications with Small Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Applications with Medium Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Applications with High Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5 5.1 5.2 5.3 5.4 5.5 Diagnosis System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Choosing the Sense Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Digital Threshold Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculation of Open Load Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculation for Partial Load Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sharing IS-Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 16 17 18 19 21 6 6.1 6.2 6.3 Required Application Accuracy for Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Define the Required Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . System Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagnosis of a P21W Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 22 22 23 7 7.1 6.4 Current Sense Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Single Point Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Calibration at 20mA with 90 Devices of 3 Lots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 10 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Application Note Smart High Side Switches 2 3 3 3 4 6 6 6 7 7 Rev 1.1, 2014-03-14 App. Note Abstract 1 Abstract Note: The following information is given as a hint for the implementation of the device only and shall not be regarded as a description or warranty of a certain functionality, condition or quality of the device. The focus of this application note is to give a guide how to calculate the diagnosis capability of a PROFET™+ in connection with a micro controller. The cases for partial loss of load, open load detection in ON-state and OFFstate are discussed. Additionally, some possible sense circuit design examples are given. 2 Introduction This application note intends to provide useful information to the designer in regards to the PROFET™+ current sense functionality. PROFET™+ is a familly of more than 20 members in the automotive field for 12 and 24V applications, offering identical features set. The familly is scaled in RDS(ON) to match the load requirements and uses current sense for load diagnosis. Current sense consists of providing a mirror current of the main load current flowing through the DMOS. A constant requirement is to achieve excellent accuracy at all load currents. PROFET™+ achieves state of the art accuracy at this point. This application note also describes in detail the calibration methods the designer can use to furthermore improve the accuracy. 3 States to Diagnose Usually the following load diagnostics are of relevance. “OFF” means the INput pin is in a LOW state. • • • • • • • • Open Load at OFF Short Circuit to Ground at OFF Nominal Load at OFF Short Circuit to Battery at OFF Short Circuit to Ground at ON Open Load at ON Partial Loss of Load at ON Overload at ON The following chapters will explain how to diagnose these cases with PROFET™+. 3.1 Diagnosis at OFF In case the PROFET™+ is in OFF state, the voltage at the output pin should be LOW as the load acts as a pulldown. If the load is disconnected, the output pin is floating and can be HIGH or LOW depending on the leakage current at the output. With the PROFET™+ it is possible to detect the Open Load at OFF and Short Circuit to Battery at OFF with the usage of external resistors. The dimensioning of these external resistors will be explained in the later chapters. 3.1.1 Open Load at OFF When the PROFET™+ is switched OFF (IN=LOW), the diagnosis can still detect a disconnected load. To support this, an external resistor ROL has to be placed between battery feed and the output, which will cause the output to go HIGH in case no load is connected. Often this connection is kept switchable via a transistor to limit the power losses and reduce the quiescent current. If the transistor T1 is used for more than one OUTput it is recommended to place a diode ( DOL ) to avoid currents flowing from one OUTput to the other. Application Note 3 Rev 1.1, 2014-03-14 App. Note States to Diagnose A typical value is: ROL = 47k T1 DOL ROL VS Cable to load OUT0 RIN IN0 RIN DEN RAD IS GND ZGND RIS PROFET+_OpenLoadOFF.vsd Figure 1 Open Load at OFF Detection 3.1.2 Short Circuit to Battery at OFF To be able to distinguish between short circuit to battery and open load at OFF, an additional pull down resistor RPD is recommended. Usually the load acts as a strong pull-down, but if this is lost, the voltage divider between ROL and RPD will cause the voltage at the output to be high enough to detect an open load. The open load at OFF comparator is battery related and therefore independent of the ground circuit and the ground shift. For more details on the detection of short circuit to battery and open load at OFF see Table 1. Typical values are: ROL = 1.5kΩ and RPD = 47kΩ. VS T1 DOL ROL VS Cable to load OUT0 RIN DEN IS RAD RPD RIN IN0 GND ZGND RIS PROFET+_OpenLoadOFF_battery.vsd Figure 2 Short Circuit to Battery at OFF Detection with ROL Application Note 4 Rev 1.1, 2014-03-14 App. Note States to Diagnose To guarantee a working diagnosis the parameter P_7.5.1 (Open load detection at OFF state) must be considered. This parameter specifies that the difference between the voltage at the OUTput pin and the supply pin (VS) must be between 0...4V (worst case) to have an OL diagnosis. With Equation (1) and Equation (2) it is possible to calculate the minimum RPD and maximum ROL. Equation (1) Known ROL. R OL × V OL ( OFF ) R PD > ----------------------------------------V S – V OL ( OFF ) (1) Equation (2) Known RPD. R PD × ( V S – V OL ( OFF ) ) R OL < ----------------------------------------------------------V OL ( OFF ) (2) It is also possible to use only a pull-down RPD resistor without the pull-up resistor ROL to do a short circuit to battery detection if no open load at OFF diagnosis is requested. (see Figure 3). Please note that the open load at OFF diagnosis is independent of the GND potential shift. VS Cable to load VS OUT0 IN0 RIN DEN IS RAD RPD RIN GND ZGND RIS PROFET+_OpenLoadOFF_battery.vsd Figure 3 Short Circuit to Battery at OFF Detection without ROL In case a LED module is used as a load and a capacitor is connected in parallel, the timing of the diagnosis can be critical. The discharging speed of the capacitor after a switch OFF depends on the pull down (load and RPD ) and has to be considered. Having just a capacitor on the output of the PROFET™+ can lead to a permanent HIGH state as the DMOS leakage might be bigger than the leakage discharge of the capacitor. Application Note 5 Rev 1.1, 2014-03-14 App. Note States to Diagnose VS Cable to load VS OUT0 IN0 RIN DEN IS RAD RPD RIN CLED LED Module GND ZGND RIS PROFET+_OpenLoadOFF_battery.vsd Figure 4 Short Circuit to Battery at OFF Detection with LED Module / without ROL 3.1.3 Nominal Load / Short to Ground at OFF A short to ground acts as a strong pull-down like the nominal load which means that it cannot be distinguished at OFF condition. The Table 1 sums up the different conditions of the load and the device output voltage. If the device ouput state is HIGH the fault current IIS(FAULT) is applied (referring to Figure 2). Table 1 Output States in OFF Condition Device in OFF state Output State T1 conducting Output State T1 open detectable and distinguishable Open Load HIGH LOW YES Short to Battery HIGH HIGH YES Nominal Load LOW LOW NO Short to Ground LOW LOW NO 3.2 Load Detection in ON For the load detection at ON state the load and sense current are considered to be settled. 3.2.1 Short to Ground at ON In this application note, the short circuit is considered as a load current that is either triggering the current limitation or thermal limitation.. At the IS-pin the PROFET™+ device provides the IIS(FAULT) current. Application Note 6 Rev 1.1, 2014-03-14 App. Note States to Diagnose 3.2.2 Short to Battery at ON Having a short to battery at ON condition would lead to a fully ON load while causing only a very small current across the PROFET™+. The resulting small current on the sense pin gives the indication that the load condition is not correct and can be misinterpreted as underload. 3.2.3 Open Load / Partial Loss / Overload at ON Before selecting the appropriate external sense resistor, the application load thresholds have to be defined. The correct definition of these areas is a key point for further calculations and design in activities. There are four areas that are of interest for the diagnosis at the micro controller: • • • • • Open Load Short Circuit Nominal Load Overload Underload As it is impossible for the diagnosis circuit to distinguish between current values that are too close to each other, there must be a grey area between LOAD and OPEN LOAD / SHORT CIRCUIT, otherwise a clear assignment is impossible. Figure 5 shows the analog values of the load current mapped to digital values on the micro controller. The micro controller should decide, based on the internal threshold definition whether the load is operating in the nominal range (LOAD) or in a failure mode (OPEN LOAD / SHORT CIRCUIT). Application Note 7 Rev 1.1, 2014-03-14 App. Note States to Diagnose Figure 5 Threshold Definition; Analog OPEN LOAD: In the case that no current is flowing (IL = 0 A) the micro controller should detect an open load, which would mean that the load is disconnected or broken. However it is often the case that although the load is not connected anymore ( RLOAD = ∞ ), a current is still flowing. This current flow can be caused by a dirt resistance RDIRT (high-ohmic connection between wires). As suggested in the PROFET™+ App Note (Chapter 6.3), RDIRT can be considered with 4.7 to 30kΩ and maximum 5mA. UNDERLOAD: The grey area represents a kind of guard band in which the current is not clearly assigned as LOAD or OPEN LOAD. Depending on the application, this area can be large or small. LOAD: This is the nominal operation range for the load and the micro controller should diagnose this as OK. The upper value (Max Load Value) should be lower than the maximum value at the micro controller to leave room for the overload detection. OVERLOAD: In this region the current is higher than the maximum nominal value but lower than the active protection treshold of the device. If this state persists, the micro controller should react on it as the increased power losses in the system can be harmful. SHORT CIRCUIT: In this case the micro controller should switch OFF the device immediately to avoid degrading the device. Application Note 8 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy 4 PROFET™+ Accuracy In each PROFET™+ datasheet, the nominal load is specified and has to be respected for partitioning. Depending on the mOhm-range of each device, certain current points for the kILIS were chosen and the values specified in the datasheet. 4.1 Definition Figure 6 provides the internal circuit principle of current sensing. The size ratio between T2 and T3 defines the mirror transformation ratio. This ratio is commonly called kILIS, meaning that the load current IL is kILIS times higher than sense current IS, IL = kILIS x IIS. The transistor T1 supplies the IIS(FAULT) current to the IS pin in case the logic detects a FAULT condition. VS T3 T1 Gate driver T2 OUT DEN FAULT OPA T4 IS sense for the baleze single . vsd Figure 6 Current Sense Circuitry 4.2 kILIS and Current Sense representation The current sense in specification is graphically represented in two possible ways. Either sketching the sense current IIS on the Y axis and load current IL on X axis as in Figure 8, or by by sketching the kILIS value on the Y axis, and load current on the X axis as in Figure 7; this curve is commonly called trumpet curve. A simple mathematical formula links the two curves. Usually the designer will prefer Figure 8 as it gives a quick read out of the current sense value. Also for an interpolation operation, this curve proves to be appropriate as the progression is nearly linear. The benefit of Figure 7 is that it shows that accuracy improves as load current increases. The Application Note Smart High Side Switches 9 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy motivation for Figure 7 is the accuracy improves with load current current increase. But it doesn’t appear as obvious as in the current IL / IIS graphic, since 8% error at 2A is higher than 50% error at 50mA in absolute value. The kILIS values that are guaranteed and tested are written down in the datasheet. However, some applications may require a calculation with unspecified kILIS values. A linear interpolation for these values can be easily performed on the IIS values (see Figure 8). 5500 5000 4500 kILIS 4000 3500 3000 2500 2000 1500 Figure 7 0 1 2 3 4 5 IL [A] 6 7 8 9 10 3 4 5 IL [A] 6 7 8 9 10 BTS5020-2EKA kILIS Trumpet 3.5 3 IIS [mA] 2.5 2 1.5 1 0.5 0 Figure 8 1 2 BTS5020-2EKA Sense Current vs. Load Current Application Note Smart High Side Switches 10 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy Note that the the PROFET™+ have the accuracy of the kilis always specified symmetrically (e.g: kILIS_typ = 3000, kILIS_max= 3240 (+8%, p1= 1.08) , kILIS_min= 2760 (-8%, p2=0.92)). However if the IIS representation is used this symmetry is lost (e.g: kILIS_typ = 3000 with +/- 8% spread, IIS_max / IIS_typ= 1.087; IIS_min / IIS_typ= 0.926) A third graphic, often omitted is necessary to provide a full picture of the current sense, is sketched on Figure 9. It provides the current sense dynamic and the load current which will be confused with a short circuit. Three different cases are shown: • • • typical: sense current in kilis mode and fault current have typical values IS_max and ISfault_min: sense current has maximum value and the fault current minimum value IS_max and ISfault_max: sense current in kilis mode and fault current have maximum values Figure 9 Current Sense Limitation Curve. BTS5020 Case This shows that the sense current (kILIS current) can be higher than the fault current. The current through the sense pin (IS) is usually limited by the sense resistor RIS and the supply voltage (VS). Details are given in the next chapter. 4.3 Power Losses in the Sense Resistor RIS Looking at the specification of the PROFET™+, the current source of the IIS(FAULT) can provide up to 35mA. For most cases it is wrong to calculate the power losses of the resistor RIS with this current IIS(FAULT)_max. As parameter P_7.5.6 (Sense signal saturation voltage) defines, the voltage at the IS pin cannot be higher than the voltage at VS. Typically it is 2V below VS. The correct calculation of the power losses is shown by Equation (3) and Equation (4). 2 ( VS – 2 ) Ploss typical = ----------------------R IS (3) 2 Ploss worstCase Application Note Smart High Side Switches VS = --------R IS (4) 11 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy The internal sense circuit is battery related and will cause an internal voltage drop; therefore the Equation (3) draws a more realistic scenario. Figure 10 shows a PSPICE simulation of a device in fault condition (Open Load at OFF) where the fault current IIS(FAULT) is applied to the external resistor RIS = 1.2k Power Loss in R IS Supply Voltage V S Sense Voltage VRIS PowerLoss _RIS.vsd Figure 10 Power Losses in RIS in Fault Condition. BTS5020 Case with Increasing Supply Voltage. 4.4 Applications with Small Currents • • • • • W3W, P5W, P10W, P21W (24V) incandescent bulbs LED Relay Stepper Motor Supply … Suggested 12V Devices: • • • BTS5120-2EKA BTS5180-2EKA BTS5200-4EKA Suggested 24V Devices: • • • BTT6100-2EKA BTT6200-1EJA BTT6200-4EMA Application Note Smart High Side Switches 12 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy Table 2 kILIS Accuracy - Small Currents Current [mA] BTS51202EKA BTS51802EKA BTS52004EKA 10 - - +/- 50% 25 - - +/- 35% 50 +/- 35% +/- 35% +/- 22% +/- 31% 1) 200 +/- 24% 1) 250 +/- 21% +/- 21% +/- 13% 1) 400 +/- 13% 1) +/- 13% 1) +/- 11% 1) 500 +/- 9% +/- 9% +/- 10% 1000 +/- 7.5% +/- 7.5% +/- 10% 2000 +/- 6% +/- 6% +/- 10% 100 +/- 31% 1) +/- 18% +/- 24% 1) +/- 14% 1) 1) interpolation value Current [A] BTT6100-2EKA BTT6200 10 - +/- 50% 25 - +/- 45% 1) 50 +/- 50% +/- 40% 100 +/- 40% +/- 28% 1) 200 +/- 27% 1) 250 +/- 22% 1) 400 +/- 15% +/- 12% 1) 500 +/- 21% 1) +/- 11% 1000 +/- 9% +/- 9% 2000 +/- 9% +/- 9% +/- 15% +/- 13% 1) 1) Interpolation Value 4.5 • • Applications with Medium Currents P21W, P27W incandescent bulbs H8 35W halogen bulb Suggested 12V Devices: • • • • BTS5020-2EKA / BTS5020-1EKA BTS5030-2EKA / BTS5030-1EJA BTS5045-2EKA / BTS5045-1EJA BTS5090-2EKA / BTS5090-1EJA Suggested 24V Devices: • • BTT6030-2EKA / BTT6030-1EKA BTT6050-2EKA / BTT6050-1EKA Application Note Smart High Side Switches 13 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy Table 3 kILIS Accuracy - Medium Currents Current [A] BTS5020 BTS5030 BTS5045 BTS5090 0.05 +/-50% +/-50% +/-50% +/-50% 0.25 +/-41% 0.5 +/-34% 1) +/-26% 1) +/-20% 1) 1) +/-23% 1) +/-23% 1) +/-16% +/-16% +/-10% +/-10% 1 +/-22% 2 +/-8% +/-8% +/-7% +/-7% 4 +/-7% +/-6.5% +/-6.5% +/-6.5% 7 +/-5.5% +/-5.5% +/-6.5% +/-6.5% +/-17% 1) interpolation value Current [A] BTT6030 BTT6050 0.05 +/-50% +/-50% 0.25 +/-45% 0.5 +/-40% 1) +/-41% 1) +/-40% 1) 1 +/-32% 2 +/-22% +/-18% 4 +/-18% +/-17% 7 +/-17% +/-17% +/-22% 1) Interpolation Value 4.6 • • Applications with High Currents H1, H3, H4, H7, H8, H9, H10 halogen bulbs (35-65W 12V) (70-75W 24V) Bulb combinations up to 100W (12V) and 147W (24V) Suggested 12V Devices: • • • • • BTS5008-1EKB BTS5010-1EKB BTS5012-1EKB BTS5016-2EKA/ BTS5016-1EKB BTS5020-2EKA / BTS5020-1EKA Suggested 24V Devices: • • BTT6020-1EKA BTT6010-1EKA Table 4 kILIS Accuracy - High Currents Current [A] BTT6020-1EKA BTT6010-1EKA 0.05 +/-50% +/-50% 1) 0.25 +/- 45% +/-45% 1) 0.5 +/-40% +/-40% Application Note Smart High Side Switches 14 Rev 1.1, 2014-03-14 App. Note PROFET™+ Accuracy Table 4 kILIS Accuracy - High Currents Current [A] BTT6020-1EKA BTT6010-1EKA 2 +/-22% +/-18% 1) 4 +/-18% +/-10% 7 +/-17% +/-9% 10 +/-17% +/-9% 1) interpolation value Current [A] BTS5008-1EKB BTS5010-1EKB BTS5012-1EKB BTS5016 BTS5020 0.05 +/-50% +/-50% +/-50% 1) +/-50% 1) +/-50% 1) 1) +/-45% 1) 0.25 +/-45% 0.5 +/-40% +/-40% +/-40% +/-40% +/-34% 2 +/-22% +/-22% +/-22% +/-22% +/-8% 4 +/-18% +/-18% +/-18% +/-18% +/-7% 7 +/-17.5% 1) +/-17.5% 1) +/-17.5% 1) +/-17.5% 1) +/-5.5% 10 +/-17% +/-17% +/-17% +/-17% +/-5.5% +/-45% +/-45% +/-45% 1) Interpolation value Application Note Smart High Side Switches 15 Rev 1.1, 2014-03-14 App. Note Diagnosis System 5 Diagnosis System Figure 11 shows the typical connections between a two-channel PROFET™+ and a micro controller. The diagnosis chain consist of measuring the load current, mirrored in the current sense, converted to voltage in the RIS resistor and read by the AD converter of the micro controller. External components mainly consist of three resistors: RIN, RIS and RADC. The external components between the device ground (GND) and the module ground is modelled as a general block and will be discussed in detail in the following chapters. ISx IISx IIS IS N1 ADC1_CH0 RADC N2 IADC V IS RIS VADC IRIS GND Figure 11 PROFET™+ with Microcontroller The most relevant current-nodes for the diagnosis circuit are marked with N1 and N2. For a simplified calculation, the voltage drop caused on RADC can be neglected as the current IADC should be very small in normal operation. 5.1 Choosing the Sense Resistor To make use of the Full Scale Range (FSR) of the microcontroller, it is recommended to take a sense resistor RIS that converts the sense current of the nominal load current to a voltage near VDD / 2. The kILIS of the PROFET™+ devices are scaled to achive the VDD / 2 at nominal load with a 1.2k to 1.8k resistor. The power losses in the sense resistor should be also considered (see Chapter 4.3). Application Note 16 Rev 1.1, 2014-03-14 App. Note Diagnosis System Adding the digital domain to the Figure 5 gives the complete picture of the diagnosis mechanism. Figure 12 Threshold Definition; Analog to Digital 5.2 Digital Threshold Calculations To calculate the digital values at the micro controller, the following parameters should be known: Table 5 Considered Inaccuracies Source of Influence Load PROFET™+ External Analog System Micro Controller Influence 1 maximum open load current kILIS values tolerance # of bits ADConverter Influence 2 nominal current range leakage currents ISx temperature coefficient Influence 3 minimum overload current Total Unadjusted Error ETUE Supply Voltage Tolerance Formulas for the sense resistor RIS Application Note 17 Rev 1.1, 2014-03-14 App. Note Diagnosis System T0 – T max × α T0 -〉 R ISmax = R IS × ( 1 + tol ) × 〈 1 + ------------------------------------------6 1 ×10 (5) T0 – T min × α T0 -〉 R ISmin = R IS × ( 1 – tol ) × 〈 1 – -----------------------------------------6 1 ×10 (6) Formulas for the Min Load Value I Lmin I ISmin = --------------------k ILISmax (7) V ISmin = I ISmin × R ISmin (8) V REFmax LSB max = ---------------------N 2 (9) V ISmin Bits min = round ⎛⎝ --------------------⎞⎠ – E TUE LSB max (10) Formulas for the Max Load Value: 5.3 I Lmax I ISmax = --------------------k ILISmin (11) V ISmax = I ISmax × R ISmax (12) V REFmin LSB min = --------------------N 2 (13) V ISmax Bits max = round ⎛⎝ -------------------⎞⎠ + E TUE LSB min (14) Calculation of Open Load Threshold The following calculation steps for the open load diagnosis takes the main inaccuracies into account, therefore an additional safety margin should be considered. The open load diagnosis can be considered as functional if the Max Open Load Current can be distinguished to the Min Load Current. In the PROFET™+ datasheets the parameter IL(OL) (Open Load detection threshold in ON state) defines the range above the open load current. Usually when the load is disconnected or broken still a leakage current can flow through the OUTput. This current can be caused by high ohmic connections of wires. Application Note 18 Rev 1.1, 2014-03-14 App. Note Diagnosis System Infineon considers 5mA as leakage current in this condition. In the test condition of IL(OL) the sense current IIS(OL) is defined. With the former assumptions, the sense current in case of open load must be smaller or equal to IIS(OL). IL(OL)_BTS5020.vsd Figure 13 Parameter: Open Load Detection Threshold in ON State; BTS5020-2EKA The graphical representation of the parameter definition of Figure 13 is shown in Figure 14. Figure 14 Illustration: Open Load Detection Threshold in ON State; BTS5020-2EKA This means if only the device accuracy is considered, it is possible to distinguish between 5mA and 30mA load current. In reality the external system tolerances force the Min Load Current threshold to increase. 5.4 Calculation for Partial Load Loss For many applications, especially with bulb and LED, multiple loads are connected to the output of the PROFET™+. It is beneficial to provide a diagnosis detecting the partial failure of the load, to meet the safety and legal requirements (i.e. flasher - 2x21W + 5W). This introduced the requirement to distinguish between the current Application Note 19 Rev 1.1, 2014-03-14 App. Note Diagnosis System range where all the loads are working as expected and the range where a partial load loss occurs. Figure 15 visualizes these areas as LOAD and PARTIAL LOAD. Figure 15 Threshold Definition for Partial Loss of Load This figure is simplified to show only the digital thresholds that separate the critical red area from the uncritical green one. It is also possible to have different software strategies for the OPEN LOAD and PARTIAL LOAD case, which introduces new digital thresholds at the microcontroller. To distinguish between a LOAD and PARTIAL LOAD the following equation, based on Equation (10) and Equation (14), must be fulfiled. Bits MaxPartialLoadValue < Bits MinLoadValue (15) V ISmax V ISmin round ⎛ -------------------⎞ + E TUE < round ⎛ --------------------⎞ – E TUE ⎝ LSB min⎠ ⎝ LSB max⎠ (16) To account for additional system inaccuracies and external factors it is recommended to have a safety margin of some LSBs between the Max Load Value and the Max PL Value. The kILIS values specified in the PROFET™+ datasheets already considers production spread, temperature spread (-40...+150°C) and lifetime drifts. No kILIS deviation over different supply voltages (8...18V) has to be taken into account. Application Note 20 Rev 1.1, 2014-03-14 App. Note Diagnosis System 5.5 Sharing IS-Pins When the design of a module with a high number of discrete components is done, there is often a shortage of available micro controller pins. With PROFET™+ it is possible to share input and/or output pins at the micro controller interface. Figure 16 shows on the example of two dual channel devices how the connection can be done. The same concept can be applied to more than two devices. It is important that both devices share the same battery supply because otherwise a coupling through the PROFET™+ exists that can lead to device destruction. For the diagnosis of all channels, the micro controller has to use the DEN and DSEL pins eg. deactivate PROFET+_2 diagnosis, activate PROFET+_1 diagnosis, select channel 0 diagnosis (DSEL=0) on PROFET+_1 and read out the IS feedback. Sharing the ADC conncection is only possible because the leakage current of the PROFET™+ on the IS pins is very small (e.g.: BTS5020-2EKA, datasheet v2.1, P_7.5.2: leakage at IS pin is maximum 1µA) VS VDD Micro controller ROL Vbat1 GPIO RIN IN0 GPIO RIN DEN GPIO RIN GPIO IN1 IS RAD OUT1 VBTOL RIS CAD PROFET+_1 DSEL RIN_DSEL A/D OUT0 GND TIS RPD_ OUT RTOL Vss ZGND Pin Sharing ROL Vbat1 VS IN0 OUT0 DEN IN1 PROFET+_2 DSEL IS GND Figure 16 RPD_ OUT OUT1 Sharing of Micro Controller Pins Application Note 21 Rev 1.1, 2014-03-14 App. Note Required Application Accuracy for Diagnosis 6 Required Application Accuracy for Diagnosis 6.1 How to Define the Required Accuracy Figure 17 describes graphically the way to define the requested accuracy. The designer should define, prior to anything else, several currents necessary to estimate the need for diagnostic. What is the maximum load current considered as open load or underload, IL(OL)_MAX, the minimum load current considered as nominal operation IL(NOM)_MIN, the maximum current considered as nominal operation IL(NOM)_MAX, and the minimum current considered as overload IL(SC)_MIN. The gap between IL(OL)_MAX ; IL(NOM)_MIN and between IL(NOM)_MAX ; IL(SC)_MIN, appearing in grey in the graphic, has to be considered as the margin the system can use during the diagnosis process. These currents will be translated to current sense IIS with the kILIS factor error. Then, this IIS current will be translated to voltage with the RIS resistor and finally converted to digital information with the A/D converter. IS RIS VIS kILIS VSC ? VL(NOM) ? VOL I OL ? I L(NOM) ? IL(OL)_MAX I L(NOM)_MAX OL IL(NOM)_MIN AD_OL I(SC) IL IL(SC)_MIN OK SC LSB # AD Figure 17 Graphical Description of the Required Current Measurement 6.2 System Influence Current sense graph .vsd The largest influence on diagnosis performance of the system is not necessarily the current sense inaccuracy of PROFET™+. The following factors will also influence the diagnostic performance of the system: • • • • A/D conversion :inaccuracy of the A/D converter, expressed in LSB (i.e. 1,3,5, etc...) A/D reference: affecting the A/D reference voltage (i.e. 0.5%, 1%, 2%, etc...) Sense resistor : inaccuracy of the sense resistor value (i.e. 0.1%, 1%, etc...) Number of devices connected to the A/D converter : if multiple current sense outputs are connected to a single A/D converter on the microcontroller, leakage currents from other devices. Application Note Smart High Side Switches 22 Rev 1.1, 2014-03-14 App. Note Required Application Accuracy for Diagnosis Addtionally, if an absolute threshold is not possible, due to inadequate margin between two currents steps (refer to the grey zone in the Figure 17), a voltage dependant threshold has to be implemented. This is shown in the example of bulb loads (see Figure 19). Therefore, additional sources of error should be considered: • • • Battery voltage measurement accuracy: accuracy of the battery voltage measurements due to the voltage divider, A/D converter accuracy, and the possible variation of the battery voltage between two battery measurements Ground shift voltage: The ground shift between the module’s ground and load ground can be a big source of inaccuracy. (shifts of up to ±1.5V should be considered). PWM inaccuracy : timing inaccuracies (i.e. differences between the turn-ON and turn-OFF time of the smart power switch) can cause a difference between the desired PWM duty cycle and actual duty cycle, affecting the equivalent lamp resistance and load current during PWM operation. In the rest of the document, the set up considered is summed up in Table 6. Table 6 System Set up Assumption Parameter Value A/D converter 10 bit A/D reference voltage 5V A/D conversion accuracy; ETUE +/- 3 LSB A/D reference voltage accuracy +/- 2% Sense resistor accuracy +/- 1% Leakage current on sense 1µA Battery voltage measurement accuracy 2% Ground shift voltage +/- 1.5V PWM inaccuracy 50µs * 100Hz = 0.5% Timing error of PWM 3% 6.3 Diagnosis of a P21W Lamp In this chapter the diagnosis of a very common bulb, the P21W is described in detail. Figure 18 shows the load current of a 21W bulb, with dependance to the supply voltage and the tolerance of the bulb itself. Two points are of interest, the minimum current of the smallest lamp at the lowest voltage, here 1.12A and the maximum current of the biggest lamps at the highest voltage, here 2.39A. Application Note Smart High Side Switches 23 Rev 1.1, 2014-03-14 App. Note Required Application Accuracy for Diagnosis 2,5 2,39 Maximum Current Typical Current Minimum Current Load Current IL (A) 2 1,5 1,12 1 6 9 12 15 VBAT (V) Figure 18 18 21W_lamp.vsd P21W Lamp Current as a Function of the Supply Voltage Of course, different usage can be considered for the P21W, summed in Figure 19 which shows that the load current IL(NOM) can be higher, either during power regulation in PWM, or during dimming with a low duty cycle. 5 Lamp current with 8% dimming Lamp current in power regulation 4,44 Lamp current in DC Load Current IL (A) 4 2,95 3 2,33 2 1 6 Figure 19 9 12 VBAT (V) 15 18 21W_ different _case .vsd Maximum P21W Load Current Depending on the Usage1) If the application is considered to be used in DC, the nominal current IL is bordered by the values [1.12A ; 2.39A.]. The open load current is considered as IL(OL)_MAX = 5mA. An open load recognition consists of distinguishing between 5mA to 1.12A. For the following calculations the specification of the appropriate PROFET™+ for a P21W bulb is used (BTS5090-2EKA). Using Equation (7) to Equation (10) for the minimum number of LSBs for the load (1.12A) and Equation (12) (using IIS(OL) = 8µA from P_7.5.2) to Equation (14) for the maximum number of bits of the open load current (5mA) 1) The slight difference of current between Figure 18 and Figure 19 comes from the difference of calculation method. Figure 18 uses a rigorous formula while Figure 19 uses only an approximation Application Note Smart High Side Switches 24 Rev 1.1, 2014-03-14 App. Note Required Application Accuracy for Diagnosis the following is obtained. Open Load Range = 0...5 LSBs; Load > 179 LSBs. This demonstrates that the P21W bulb can be easily diagnosed using PROFET™+. Often it is necessary to support both a bulb and LED on the same BCM and provide a load diagnosis. A equivalent replacement of the P21W bulb would be a 4W LED with approximately 200mA load current. Keeping the above assumptions and changing to the 4W LED results in: Open Load Range = 0...5 LSBs; Load > 40 LSBs. This means also for an LED the diagnosis is feasible. Application Note Smart High Side Switches 25 Rev 1.1, 2014-03-14 App. Note Current Sense Calibration 7 Current Sense Calibration Specified kILIS values in the datasheet are guaranteed values and must be valid under all conditions. The minimum and maximum values have to account for lifetime drifts, production spread, voltage and temperature dependencies. Effects of the lifetime drift is not predictable and must be considered through approximations. As a result of this, one individual device shows much better accuracies if some of these factors are eliminated. Figure 20 shows the accuracy of a singular BTS5020-2EKA device over different currents and at three termperatures. The accuracy is related to the kILIS value at 4A at 25°C which is 3000. Identifying this kILIS value is equal to a one point calibration at room temperature. Figure 20 BTS5020-2EKA Zero Hour kILIS Performance Smaller currents are more prone to the influences of the operational amplifier in the sense circuit. As a consequence it does not make sense to do a calibration at smaller load currents. For the BTS5020-2EKA the datasheet specifies that a calibration for currents bigger or equal to 2A is valid. In case the current sense accuracy is not precise enough, calibration can be considered. The calibration point(s) choice is of primary importance to reach the best possible accuracy. This chapter describes the results applied to the BTS5020-2EKA. By analogy, all PROFET™+ can be described with this method. 7.1 Single Point Calibration Single point calibration compensates the kILIS ratio error (mismatch between the current sense DMOS cells and the main DMOS). It is not compensating systematic error linked to the operational amplifier offset and will not compensate the aging. Figure 21 shows as example, the results of a calibration realized at 1A and kILIS ratio measured at 7A, and the opposite. The blue color indicates the cold (-40°C) test, green indicates ambient and red hot (150°C) temperature. The different lines for a given color, indicates the drift observed due to aging. The X-axis express the drift in percent, while the Y-axis provides the probability to find a device with such derating. Three lots, 30 samples each are tested. Application Note Smart High Side Switches 26 Rev 1.1, 2014-03-14 App. Note Current Sense Calibration Figure 21 BTS5020-2EKA Calibrated at 1A (resp 7A) and Measured at 7A (resp 1A) with Aging Out of these graphs, we can extract the Table 7, indicating both temperature, calibration point and load current influence. Table 7 Calibration results of the BTS5020-2EKA in Percent of Error Calibrated at Measured at 1A 2A 4A 7A 1A 2A 4A 7A -40°C -3 ; +2,5 -2 ; +2 -2,5 ; 2 -3,5 ; +3 +25°C -1 ; +1,5 -1,5 ; +2,5 -2,5 ; 3 -3,5 ; +3,5 150°C -1 ; +3 -1,5 ; +4,5 -2 ; +5 -2,5 ; +4,5 -40°C -5 ; +3,5 -2 ; +1 -1 ; +1 -2 ; +1 25°C -2 ; +2 -0,5 ; +1 -1 ; +1,5 -2 ; +1,5 150°C 0 ; +2 -0,5 ; +2,5 -1 ; +3 -1 ; +3 -40°C -6 ; +5 -3 ; +2 -1,5 ; +1 -1 ; +0 +25°C -4 ; +3 -1,5 ; +1,5 0 ; +1 -1 ; +1 150°C -0,5 ; +2 0 ; +2 0 ; +2 -0,5 ; +2 -40°C -6 ; +5 -3 ; +2,5 -1,5 ; +1 -1 ; +0,5 +25°C -4 ; +4 -1,5 ; +2,5 -0,5 ; +1 0 ; +1 150°C -1 ; +2 0 ; +2 0 ; +2 0 ; +2 As temperature is quite difficult to take into account during software programming, Table 7 can be reduced to Table 8. Table 8 Calibration results of the BTS5020-2EKA in Percent of Error Calibrated at Measured at 1A 2A 4A 7A Datasheet 1A All temp +/- 3 +/- 4,5 +/- 5 +/- 5 +/- 21%1) 2A All temp +/- 5 +/- 2,5 +/- 3 +/- 3 +/- 8% 4A All temp +/- 6 +/- 3 +/- 2 +/- 2 +/-7% 7A All temp +/- 6 +/- 3 +/- 2 +/- 2 +/-5.5% 1) Estimated by linearization Application Note Smart High Side Switches 27 Rev 1.1, 2014-03-14 App. Note Current Sense Calibration Figure 22 BTS5020. Calibration at 1A and expected Accuracy along the Load Current Table 9 is the prolongation of the BTS5020-2EKA analysis. Table 9 Calibration results of the PROFET™+ BTS5020-2EKA in Percent of Error Measured at Half IL(2) IL(2) IL(3) IL(4) Datasheet Half IL(2) All temp -3 ; +3 -2 ; +4,5 -2,5 ; +5 -3,5 ; +4,5 +/- 21%1) IL(2) IL(3) IL(4) All temp -5 ; +3,5 -2 ; +2,5 -1 ; +3 -2 ; +3 +/- 8% All temp -6 ; +5 -3 ; +2 -1,5 ; +2 -1 ; +2 +/- 7% All temp -6 ; +5 -3 ; +2,5 -1,5 ; +2 -1 ; +2 +/- 5.5% Calibrated at 1) Estimated by linearization 6.4 Calibration at 20mA with 90 Devices of 3 Lots To evaluate the calibration performance of the PROFET™+ a limited number of devices of the 45mOhm and 30mOhm dual channels were tested at three temperatures. This data shows the reachable accuracy at zero hour (no lifetime influence) with a single point calibration at a current of 20mA and 25°C ambient temperature and the deviation in percent at -40 and +150°C. At this low current the device is working in gate back regulation. Application Note Smart High Side Switches 28 Rev 1.1, 2014-03-14 App. Note Current Sense Calibration 100 90 1 80 0.8 70 60 0.6 50 40 0.4 30 20 0.2 10 0 -15 -10 Figure 23 -5 0 Accuracy in % 5 10 0 -10 -5 0 5 Accuracy in % 10 BTS5045_calibration_20mA.vsd BTS5045-2EKA. Calibration at 20mA and Expected Accuracy. 100 90 1 80 0.8 70 60 0.6 50 40 0.4 30 20 0.2 10 0 -40 -20 0 20 40 60 80 0 -50 -40 -30 -20 -10 0 10 Accuracy in % Figure 24 20 30 40 50 BTS5030_calibration_20mA.vsd BTS5030-2EKA. Calibration at 20mA and Expected Accuracy. The left side of the Figure 23 and Figure 24 shows the number of devices that have a certain in-accuracy at -40 and +150°C. A total number of 90 devices (30 pcs of 3 lots) was tested. On the right side, the cumulative distribution function is shown. Application Note Smart High Side Switches 29 Rev 1.1, 2014-03-14 App. Note Conclusion 8 Conclusion The PROFET™+ Family offers very accurate sense feedback to the microcontroller. With the right choice of the device and the external components, the diagnosis is easily implementable in the microcontroller. The SMART6 technology that is used for PROFET™+ proves to be very accurate for kILIS relevant circuits like the op-amp and DMOS matching of the Sense- and Power-DMOS. Aging effects caused by electrical stress do not show a drastic effect on the accuracy of the sense circuit as is was shown in Chapter 7.1. Application Note Smart High Side Switches 30 Rev 1.1, 2014-03-14 App. Note Glossary 9 Glossary Table 10 Symbol and Abbreviation Symbol AEC Unit Meaning - Automotive Electronic Council αT0 EAS EAR ETUE temperaturcoefficient 1st order at temperature T0 J Maximum inductive energy switchable once by the device over life time J Maximum inductive energy switchable by the device repetitively LSB Total Unadjusted Error; This is the deviation between the Ideal Transfer Function and the actual one FSR Full Scale Range GBR - Gate Back Regulation GND - GrouND IADC IIS INOM IL IL(RMS) IINRUSH ITRIP IL(SC) IL(SC)_TYP IL(SC)_MIN IL(SC)_MAX IRIS kILIS A Current that flows from or into into the ADC of the µC A Current of the sense; IS Pin A Nominal current of a device A Load Current; Current through OUTput pin A Root Mean Square of the Load Current, also called true current A Inrush current due to the load A Short Circuit Tripping current, threshold where device switches OFF A Short Circuit Limiting current (limited by device or by short circuit impedance) A Typical short circuit current A Minimum short circuit current A Maximum short circuit current A Current through the sense resistor RIS ratio between IL and IIS LSB Least Significant Bit LSupply LShort nRSC1 H Parasitic supply inductivity due to wire harness, also called primary inductance H Parasitic load inductivity due to wire harness, also called secondary inductance Op. Amp - Operational Amplifier OEM - Original Equipment Manufacturer PWM - Pulse Width Modulation RSupply RShort Rtc Ω Parasitic supply resistance due to wire harness, also called primary resistance Ω Parasitic load resistance due to wire harness, also called secondary resistance SC1 - Short Circuit type 1. Device switches into short circuit SC2 - Short Circuit type 2: The switch is ON while a short circuit occurs tol % Tolerance TJ TJ(SC) TJ(MAX) ΔT °C Junction temperature of the DMOS °C Overtemperature threshold °C Maximum acceptable temperature of silicon K Temperature difference between TJ and TREF cycle Number of short circuit cycle the device can withstand before destruction Application Note Smart High Side Switches 31 Rev 1.1, 2014-03-14 App. Note Glossary Table 10 Symbol Symbol and Abbreviation Unit Meaning ΔTIND K Temperature overshoot due to inductive switch OFF ΔTRST K Restart hysteresis after ΔT switch OFF. ΔTJ(SC) K Restart hysteresis after TJ(SC) switch OFF TREF TC T tON tOFF tLIM tCOOL tRETRY tLATCH_WAIT VGS VBB VREF VS VDS °C Temperature reference of the device °C Leadframe or case temperature of the device s Period of a frequency signal s Time while the input pin is set to logical level “1” or HIGH s Time while the input pin is set to logical level “0” or LOW s Time while the device actively limits the short circuit current s Time while the device is OFF to cool down after over thermal event s Time while the application is still discriminating between inrush and short circuit s Time while the device waits before restarting. V Gate source voltage of DMOS V Battery Voltage V Voltage supply of the micro controller V Supply Voltage V Drain source voltage of DMOS Application Note Smart High Side Switches 32 Rev 1.1, 2014-03-14 App. Note Revision History 10 Revision History Version Date Changes 1.1 2014-03-14 Upated kilis accuracy in chapter 4.4 / 4.5 and 4.6 Added 24V PROFET™+ Removed -2LAA devices because of product discontinuation Changed in Formula (13) LSB_max to LSB_min Added Chapter 5.5 1.0 2012-10-25 Creation of the document Application Note Smart High Side Switches 33 Rev 1.1, 2014-03-14 Edition 2014-03-14 Published by Infineon Technologies AG 81726 Munich, Germany © 2014 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. 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