Application note, Rev 0.0, June 2010 PROFET+ Current Sense with Low Battery Voltage PROFET + Application note By Stéphane Fraissé Automotive Power IIS at Low VBAT 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. This application note provide information about the current sense SENSE behaviour during low battery voltage. It shows possibilities and limitation of the PROFET + devices during phases where the battery voltage falls down close to the undervoltage shutdown of the PROFET +. 2 Introduction All terms and physical quantity discussed in the current application note are sumed up in Figure 1. The schematic is simplified in regards to the real application to ease up the understanding. The real application schematic can be found in the PROFET + data sheet in usage. The schematic consists in a PROFET + device, supplied on its VS pin via the battery voltage called VBAT. GND pin of the PROFET + is connected to the GND of the system via a GND network. The current consumption of the PROFET + is called IGND. The voltage drop which is resulting of the GND network and IGND is called VGND_SHIFT. The PROFET + switches a load L and a load current IL flows. L has a certain impedance resulting a voltage VOUT. The PROFET + provides load diagnosis via the IS pin. The output current is called IIS. The IIS current is converted to a voltage VIS via a RIS resistor. The voltage is read by a micro controller for system diagnosis with a A/D converter. To protect the A/D stage of the micro controller, a resistor RA_D is used. Two additional voltages related to the battery voltage VBAT are defined. VS, effective supply voltage of the PROFET + and VIS_DROP, representing the voltage between battery voltage and current sense pin IS. The micro controller is supplied by a voltage VDD, referenced to GND. VIS_DROP VBAT VS IIS IIS(FAULT) VS VDD VDD OUT IA_D RA_D IS A/D VA_D IL GND VIS IIS VOUT IGND GND VGND_SHIFT RIS GND Network L SF_Circuit_equivalent.svg Figure 1 Hardware simplified Schematic Application note PROFET + 2 Rev 0.0, 2010-06-30 IIS at Low VBAT SENSE Behaviour in Nominal Operating Range 3 SENSE Behaviour in Nominal Operating Range The SENSE provided at the IS pin is proportional to the load current IL. Figure 2 shows as an example the function IIS = f (IL) of the BTS5020-2EKA. Because the current sense generator IIS is not perfect and is not matched to IIS_FAULT, the maximum diagnosable load current is limited. This limitation is called SENSE dynamic. It is in the range of 19A for the BTS5020-2EKA. At this load current, the SENSE is at least 6mA. With higher load current, the BTS5020-2EKA cannot guarantee analog diagnosis and the information is mixed with failure (short circuit) information. The voltage representation of the Figure 2 can be found in the Figure 3. The resistor RIS is coresponding to the datasheet suggested value so 1.2kΩ. In such a representation, it is assumed the is not connected to the micro controller. Therefore, no voltage limitation of the IS pin takes place. The second assumption is the battery voltage is high enough to provide such an high voltage shown on the graphic, up to 16.8V. Figure 4 is the representation of the SENSE pin and its representation at the A/D converter, the VA_D potential. Figure 5 becomes the software compatible representation of the load current assuming a 10bit AD. 16 I sense all max I sense max I fault min 14 I sense typical I sense min I fault max Sense Current IIS (mA) 12 I sense all min 10 8 LINEAR 6 BEHAVIOR SATURATION BEHAVIOR OF IIS OF I IS 4 SWITCH TO IIS_FAULT 2 0 0 20 #17A Figure 2 40 60 Load Current IL (A) 80 100 SF_sense Normal .vsd SENSE Function of the Load Current with BTS5020-2EKA 18 V sense all max 16 V sense max I fault min SENSE Voltage VIS (V) 14 V sense typical V sense min I fault max 12 V sense all min 10 8 6 4 2 0 0 Figure 3 20 40 60 Load Current IL (A) 80 100 SENSE Voltage Function of the Load Current with BTS5020-2EKA Application note PROFET + 3 Rev 0.0, 2010-06-30 IIS at Low VBAT SENSE Behaviour in low Battery Operating Range 6 V sense all max V sense max I fault min 5 V sense typical V sense min I fault max A/D Voltage VA_D (V) V sense all min 4 3 2 1 0 0 Figure 4 5 #13A 15 10 Load Current IL (A) 20 25 SF_sense Voltage _ avec _Limitation .vsd A/D Voltage Function of the Load Current with BTS5020-2EKA SENSE Voltage (DIGITAL) 1024 960 V sense all max 896 V sense min I fault max 832 V sense typical V sense min I fault max 768 V sense all min 704 640 576 512 448 384 320 256 192 128 64 0 0 5 10 #12A 15 Load Current IL (A) 20 25 SF_sense Voltage _ DIGITAL.vsd Figure 5 A/D representation Function of the Load Current with BTS5020-2EKA 4 SENSE Behaviour in low Battery Operating Range During low battery operation, the behaviour of the SENSE doesn’t differ so much from the Nominal Operating Range. The limitation comes from the maximum voltage the IS pin can provide. The PROFET + datasheet defines the parameter VIS_RANGE (parameter P_7.5.6). This voltage should be at least 3V. The voltage drop between VS and IS pins (VIS_DROP) should be at least 3V to have a proper diagnosis. In a theoretical possible but application useless case, with IS pin shorted to GND, the Figure 2 remains correct down to the under voltage shutdown of the PROFET + so 3.5V typical VS. Let’s consider for example, VBAT = 6V, resulting in a VS voltage of 5V (assuming the VGND_SHIFT = 1V). VIS cannot the be higher than VBAT = 6V and can be down to VBAT - 3V = 3V min. With such assumption, Figure 3 becomes much different and it shown on Figure 6. The SENSE dynamic is now 8.5A instead of the former 19A. Figure 4 becomes Figure 7 and Figure 8 show the SENSE dynamic translated to the micro controller port A/D. Application note PROFET + 4 Rev 0.0, 2010-06-30 IIS at Low VBAT SENSE Behaviour in low Battery Operating Range 6 SENSE Voltage VIS (V) 5 4 3 V sense all max V sense max I fault min 2 V sense typical V sense min I fault max 1 V sense all min 0 0 Figure 6 #8.5A 20 40 60 Load Current IL (A) 80 100 SF _sense Voltage _ sans _Limitation_LOWVBAT .vsd SENSE Voltage Function of the Load Current with BTS5020-2EKA 6 V sense all max V sense max I fault min 5 V sense typical A/D Voltage VA_D (V) V sense min I fault max V sense all min 4 3 2 1 0 0 5 10 15 Load Current IL (A) 20 25 SF_sense Voltage _ avec _Limitation_LOWVBAT . vsd Figure 7 A/D Voltage Function of the Load Current with BTS5020-2EKA 1024 960 V sense all max 896 V sense typical 832 SENSEVoltage (DIGITAL) 768 V sense all min 704 640 576 512 448 384 320 256 192 128 64 0 0 Figure 8 5 # 8,5A 10 15 Load Current IL (A) 20 25 SF_sense Voltage _ DIGITAL_LOWVBAT . vsd A/D Voltage Function of the Load Current with BTS5020-2EKA Application note PROFET + 5 Rev 0.0, 2010-06-30 IIS at Low VBAT Conclusion The SENSE dynamic is limited during low battery operation by the VIS voltage. Taking the BTS5020-2EKA as an example, from a SENSE dynamic of 16.5A, the value can goes down to 8.5A so half the value. In other words, the BTS5020-2EKA signals a load current higher than 8.5A the same way than a short circuit with a VBAT of 6V. The micro controller should interpret a voltage of 3V at the A/D converter as a short circuit event if the battery voltage is 3V. At first sight, this value can appear low but it should be balanced to the effective load current at 6V VBAT. Table 1 sums up the SENSE dynamic of all PROFET + devices and Table 2 shows the maximum current the planned load exhibits at 6V battery. There is no overlapping and even good safety margin. Table 1 PROFET + SENSE Dynamic mΩ 8 10 12 16 20 30 45 kILIS_TYP IL_MAX SENSE dynamic 4500 4250 4000 3500 3000 2150 1500 27.4 25.8 24.3 21.3 16.6 11.9 8.3 9.8 9.2 8.7 7.6 6.9 4.9 3.4 90 120 180 1500 550 550 8.3 3.0 3.0 3.4 1.2 1.2 13.5V IL_MAX SENSE dynamic 6V Table 2 PROFET + Load Current mΩ 8 10 12 16 20 30 45 90 120 180 LOAD (W) 65 55 3x27+ 5 55 2x27+ 5 2x21 27 21 10 5 IL_MAX in DC (no PWM) 5.3 4.5 7.3 4.5 5.0 3.9 2.3 2.0 0.8 0.4 3.5 3.0 4.9 3.0 3.3 2.6 1.5 1.3 0.5 0.3 13.5V supply IL_MAXin DC (no PWM) 6V supply 5 Conclusion Using PROFET + at low battery voltage is possible. The diagnosis works with limitation. The micro controller should monitor the current battery voltage and interprets A/D information accordingly. 6 Revision History PROFET+ Current Sense with Low Battery Voltage Revision History: Rev 0.0, 2010-06-30 Previous Version(s): Rev. 0.0, 2010-06-30 Page Subjects (major changes since last revision) Application note PROFET + 6 Rev 0.0, 2010-06-30 Edition 2010-06-30 Published by Infineon Technologies AG 81726 Munich, Germany © 2010 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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