AN1305 TD340 TS922A STP60NE-06L 1N4148 TS922 R21//R22 R19-R22

APPLICATION NOTE CURRENT MEASUREMENT AND LIMITATION IN TD340 BASED MOTOR CONTROL SYSTEMS by J. CAMIOLO and J-F GARNIER Two main

AN1305 AN1305 APPLICATION NOTE CURRENT MEASUREMENT AND LIMITATION IN TD340 TD340 BASED MOTOR CONTROL SYSTEMS by J. CAMIOLO and J-F GARNIER Two main configurations can be used: - sense resistor between the bottom of the H-bridge and the Gnd line (low side sensing). - or sense resistor connected between the Vbat line and the top of the H-bridge (high side sensing) Each configuration has its own advantages and disadvantages, and the choice of the right method depends on the application Figure 1 : Low Side Sensing VcarBat 4 In motor control applications, it is very useful to monitor the current through the motor. The current value is an image of the motor torque which is of great interest for motion control. The over current monitoring can be used to detect end of motion conditions and thus avoid the use of a position sensor. It is also useful to provide security functions like motor stall detection and short circuit protection. The threshold is set by resistors R17 and R18 from the 5V supply. The R15, C3 network acts as a filter to reject short overcurrent conditions, e.g. at motor startup. U2B 7 Overcurrent Out + TS922A TS922A C3 1nF 6 Qreverse STP60NE-06L STP60NE-06L 5V R16 R15 10K 2.1 Description Figure 1 shows the operating principle. The dual operational amplifier TS922A TS922A (U2A and U2B) is powered by the 5V coming from the TD340 TD340. The TS922A TS922A is a rail to rail device with a low input offset voltage (0.9mV max.) and is well suited for this application. The voltage across the shunt resistor (Vsens) is amplified with the op-amp U2A. The voltage at the op-amp output is: V(I reading) = Vsens * (R13+R14) / R13 The R11, C5 network is used to remove the PWM frequency (25kHz typ.). Cut frequency is about 1kHz, providing a response time of a few milliseconds for the current information. The second op-amp U2B is used to implement an overcurrent security. U2B is used as a comparator and provides an emergency signal to the µC when an overcurrent occurs. October 2000 R17 10K STP60NE-06L STP60NE-06L Q2H Q1H 560K U2A TS922A TS922A + 1 I Reading Out R14 47K 5V Q2L Q1L STP60NE-06L STP60NE-06L 3 C5 2 100nF R13 10K R11 10K Rsens This application note describes some solutions that can be used with the TD340 TD340, a quad MOSFET driver in H-bridge configuration. 2. SOLUTION WITH THE SENSE RESISTOR CONNECTED IN THE GND WIRE R18 10K 5 8 1. INTRODUCTION I Vsens 2.2 Full Schematic Figure 2 shows the complete application schematic. The current reading signal is connected to a A/D input port of the micro-controller (µC), and the overcurrent signal (active low) is wired to an interrupt input. Furthermore, the overcurrent signal immediately brakes the motor by pulling low the IN1/IN2 lines of the TD340 TD340 with diodes D3, D4. This feature provides a fast hardware current limitation. As soon as the current drops below the threshold (including the hysteresis), the IN1/IN2 lines are released and the TD340 TD340 is controlled again by the µC. 2.3 Comments Advantages: -easiest method, -precise, low offset, no calibration needed. Disadvantage: -unable to detect load shorted to ground. 1/6 AN1305 AN1305 - APPLICATION NOTE Figure 2 : Low Side Sensing, Full Application Schematic VcarBat Vcarbat 1 D2 1N4148 1N4148 C4 10µf Vcc 1 Stby 2 ST6xx Reset 3 Cwd 4 5 6 7 Temp Reading Speed Direction R26 8 R25 2K2 2K2 C1 1N4148 1N4148 100pF Vbat Qreverse STP60NE-06L STP60NE-06L RReset 10K µController Watchdog D1 + 5V RStBy CVout 10K 220nF R1 680K Vboost 9 10 Current reading Vbat Osc Vout Cb1 Reset H1 Cwd S1 Wd Cb2 Stby H2 Temp S2 In1 L2 In2 L1 Cf Gnd R2 20 19 Cb1 47nF 18 5K6 RQ1H 17 16 Cb2 47nF 15 STP60NE-06L STP60NE-06L Q2H Q1H RQ2H 14 13 12 Q2L Q1L STP60NE-06L STP60NE-06L RQ2L RQ1L 11 U1 Overcurrent TD340 TD340 Gnd R11 U2A 1 + Out - TS922 TS922 D4 1N4148 1N4148 3 10K C5 100nF 2 R13 R14 47K D3 1N4148 1N4148 5V R15 100K R17 10K 8 560K 5V + Out 4 U2B TS922 TS922 2/6 10K Gnd R16 7 Rsens 5 6 R18 10K C3 47nF 1 AN1305 AN1305 - APPLICATION NOTE 3. SOLUTION WITH THE SENSE RESISTOR CONNECTED IN THE VBATT WIRE Figure 4 : Op-Amp Protection VcarBat=60V 3.1 Description If a fifth MOSFET is used to protect against battery connection reversal (see the TD340 TD340 datasheet), it can be used as a sense resistor. In normal mode the Q transistor is always on and has a very small Rdson resistance. An additional advantage from using the MOS resistance is that it provides a lower current limitation at higher temperature as the Rdson is increasing. Figure 3 shows the operating principle. The voltage at the op-amp output is: Vsens VBat Rsens ESD diode R12 220K 5V + 2mA R13 R19 47K R21 47K IR13 V1 20K - R11 V2 20K R14 R20 15K R22 15K 220K V(Ireading) = Vsens * R22 / (R21+R22) * R14 / (R11 + R21//R22 R21//R22) Rx//Ry means Rx parallel with Ry. Conditions are: R19=R21, R20=R22, R11=R13 and R12=R14. Figure 3 : High Side sensing Qreverse VcarBat I VBat Vsens R12 220K U2A TS922 TS922 1 Ireading 3 + Out R14 2 R19 47K R21 47K R13 20K Q2H Q1H R11 20K 220K STP60NE-06L STP60NE-06L 5V R16 R15 10K R17 10K R20 15K R22 15K 8 560K 5V 7 + Out U2B TS922 TS922 4 Overcurrent Q2L Q1L 5 R18 10K 6 C3 1nF High common mode voltage The major problem with this configuration is the high common mode voltage at the sense resistor. Moreover, in automotive applications, the Vbatt voltage can rise to more than 40V during 'load dump' transients. The TD340 TD340 can sustain such voltage (up to 60V), but the op-amp has to be protected as well. This can be done with resistor bridges at each side of the sense resistor to lower voltages to acceptable level. Resistor ratio of 1:3 provides a 1/4 attenuation of common voltage that can then rise near to 20V. Greater voltages are not functional but are harmless for the op-amp because the voltages at input pins are clamped by diodes to the 5V supply and the serial resistors limit the current into the input pins to acceptable levels (see figure 4). Of course, differential voltage is reduced as well, a typical 200mV shunt voltage gives only 50mV after the resistor bridge. Voltage range To achieve a good common mode rejection, precision resistors (at least 0.1%) should be used. If the common voltage range is 12V to 16V, the common voltage range after the resistor bridge is 3V to 4V. A 0.1% mismatch between each arm of the resistor bridge produces a change of 1mV differential voltage, i.e. a 2% systematic error (1mV relative to 50mV). Moreover, the 1V common mode voltage change seen by the op-amp also produces an error due to the finite CMRR of the op-amp: 1 mV for a standard 60dB rejection ratio. This shows that this method only works with limited common voltage range. Offset The total offset is due to the intrinsic offset of the op-amp, plus the offset due to the various resistor mismatch. As this offset is not negligible, it must be corrected by software. The µC must proceed to an auto zero calibration when the motor is off (at each power-up for example). However, the offset can be positive or negative, so the zero current level at the input of the µC should not be 0V, but a small positive value. This is the purpose of R23 and R24 that provide a shift of about 500mV. 3.2 Full schematic The full schematic is showed in figure 5 and includes an overcurrent protection built with a second op-amp used as a comparator. 3.3 Comments Advantages: -detection of load shorted to ground, -use of the 5th MOSFET as sensing resistor. Disadvantages: -need of high precision resistors, -need of a software auto-zero calibration. 3/6 AN1305 AN1305 - APPLICATION NOTE Figure 5 : High Side Sensing with Resistor Bridge, Full Schematic VcarBat Vcarba 1 D2 1N4148 1N4148 C2 470µf CVout 1 µController Stby 2 ST6xx Reset 3 Cwd 4 Watchdog 5 6 Temp Reading 7 Speed R26 Direction R25 8 2K2 9 2K2 C1 1N4148 1N4148 100pF Vbat Qreverse STP60NE-06L STP60NE-06L RReset 10K 220nF Vcc D1 + 5V RStBy 10K R1 680K Vboost 10 Current reading Vbat Vout 19 Cb1 Reset H1 Cwd 16 S2 In1 L2 In2 RQ1H Q2H Q1H RQ2H STP60NE-06L STP60NE-06L 14 13 RQ2L 12 RQ1L Q2L L1 Cf Cb2 47nF 15 H2 Temp 5K6 17 Cb2 Stby Cb1 47nF 18 S1 Wd R2 20 Osc Gnd Q1L 11 Gnd 1 U1 Overcurrent TD340 TD340 5V Gnd R23 2.2M U2A TS922A TS922A 1 Out R14 2.2M 20K R19 47K R21 47K R12 220K 5V D3 1N4148 1N4148 V2 R11 220K R24 D4 1N4148 1N4148 20K 2 - V1 R13 3 + R20 15K R16 R15 100K R22 15K C3 47nF 8 560K 5V R17 10K 7 + Out 4 U2B TS922A TS922A 4/6 - 5 R18 10K 6 C5 47nF R11- R14, R19-R22 R19-R22: 0.1% C4 47nF AN1305 AN1305 - APPLICATION NOTE 4. ALTERNATE SOLUTION WITH THE SENSE RESISTOR CONNECTED IN THE VBATT WIRE 4.1 Description Using the sense resistor in high side position has a lot of advantage, but is usually difficult to handle. The following schematic (figure 6) shows an alternate solution using a floating op-amp near the Vbatt line. VcarBat I Vsens R11 1K C3 1nF R10 20K 2 Q2H Q1H 3 - 5. CONCLUSION U3A Out + Advantages: -detection of load shorted to ground, -precise, low offset, no calibration needed. Disadvantages: -2 independent op-amps ICs -more discrete parts. Measuring the current in motor control application is often required. Choosing the right method for current measurement and limitation requires careful reviewing of the advantages and disadvantages of each configuration. For automotive applications, a high side sensing will often be preferred, whereas industrial or cost sensitive applications will use simpler low side sensing. Figure 6 : High Side Sensing Qreverse STP60NE-06L STP60NE-06L 4.3 Comments TS922A TS922A 1 Q3 PNP STP60NE-06L STP60NE-06L VcarBat-5V Q2L Q1L Ireading R12 10K Operation The principle is to use a op-amp supplied near to Vbatt to measure the differential voltage across the shunt. This op-amp is supplied between Vbatt and an intermediate voltage at about 5V below Vbatt. The op-amp operates close to the upper rail, and converts the shunt voltage into a current by the means of resistor R11 and transistor Q3. Resistor R12 converts back this current into a voltage near the ground level where it can be easily used by the µC or additional circuit. The I reading voltage is: V(I reading) = Vsens * R12 / R11 4.2 Full schematic The full schematic (figure 7) includes overcurrent protection build with a independent op-amp used as a comparator. The intermediate voltage for U3 is built with Zener diode Z1 and transistor Q4. If the application have to withstand 'load dump' transients, Q1 and Q4 should be rated at least to 60V. 5/6 AN1305 AN1305 - APPLICATION NOTE Figure 7 : High Side Sensing with Floating Op-Amp, Full Schematic Vcarbat VcarBat 1 D2 1N4148 1N4148 C2 470µf + 5V RStBy CVout 10K 220nF Vcc 2 Reset 3 Cwd 4 5 6 Direction 7 R26 8 R25 2K2 9 2K2 Current reading R11 1K C3 1nF R10 20K 1 Stby Speed Qreverse STP60NE-06L STP60NE-06L RReset 10K ST6xx Temp Reading C1 1N4148 1N4148 100pF Vbat µController Watchdog R1 680K Vboost D1 10 Vbat Osc Vout Cb1 Reset H1 Cwd S1 Wd Cb2 Stby H2 Temp S2 In1 L2 In2 L1 Cf Gnd R2 20 19 Cb1 47nF 18 3 RQ1H - U3A 1 Out + TS922A TS922A 16 Q3 6V PNP Q4 17 Cb2 47nF 15 Q2H Q1H PNP RQ2H STP60NE-06L STP60NE-06L 14 R14 13 RQ2L 12 RQ1L 10K Q2L Q1L 11 Gnd U1 Overcurrent Z1 2 5K6 1 TD340 TD340 Gnd U2A TS922A TS922A 1 + Out - D4 1N4148 1N4148 D3 1N4148 1N4148 3 2 R13 22K 5V R12 10K R16 R15 100K R17 10K C4 47nF 8 560K 5V 7 + Out 4 U2B TS922A TS922A - 5 6 R18 10K C5 47nF R11- R14, R19-R22 R19-R22: 0.1% Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. © The ST logo is a registered trademark of STMicroelectronics © 2000 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom © http://www.st.com 6/6