AN1088 STMICROELECTRONICS | Alldatasheet

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5A. It can be used in a very wide range of applications. and in Power SO 20 packages. current of 6.5 mA typ. at Vs=42V , irrespective of the load. ture exceeds approximately 160 °C. Hysteresys is about 20 °C. Figure 1. L6234 Block Diagram

Cross conduction protection (see Fig. 7) avoids simultaneously turning on both the upper and lower DMOS of each half bridge. There is a fixed delay time of 300ns between the turn on and the turn off of the two DMOS switches in each half bridge. The switching operating frequency is up 50kHz. High com- mutation frequency permits the reduction of ripple of the output current but increases the device’s power dissipation, however low commutation frequency causes high ripple of the output current. The switching frequency should be higher than 16kHz to avoid acoustic noises. The sink current at the INPUTS and ENABLES pins is approximately 30µA if the voltage to these pins is at least 1V less than the Vref voltage (see Fig. 3 and Fig. 4). To avoid overload of the logic INPUTS and ENABLES , voltage should be applied to Vs prior to the logic signal inputs. POWER DISSIPATION An evaluation of the power dissipation of the IC driving a three phase motor in a chopping current con- trol application follows. With a simplified approach it can be distinguished three periods (see Fig. 8) : Rise Time, Tr, period. This is the rise time period, Tr, in which the cur- rent switches from one winding to another. In this time a DMOS is switched on and the current in- creases up to the peak value Ipk with the law i(t) = (Ipk/Tr) t. The energy lost for the rise time in the period T is : Erise = Tr Rdson ⋅ i2(t)dt = Rdson ⋅ I2pk ⋅ Tr Fall Time,Tf, period. When the current switches from one winding to another, there is a fall time in which the current that flows in the intrisic diode of the DMOS de- creases from Ipk to zero. If VD is the voltage fall of the diode, the energy lost is : Efall = tf VD (t) ⋅ i(t)dt Tload During this time the current that flows in the winding is limited by the chopping current control. The en- ergy dissipated due to the ON resistance of the DMOS is : Eload = Rdson ⋅ (Irms)2 ⋅ Tload In the formula, Irms is the RMS load current, given by : I pk − Ival √3 and Iload is the average load current. When the switch is ON, the energy dissipated due to the commutation of the chopping current control in the DMOS can be assumed to be: Eon = Vs ⋅ Ival ⋅ tcom where tcom is the commutation time of the DMOS switch. Trise TfallTload Tchop Ipk Ival Iload Figure 8. AN1088 APPLICATION NOTE

360˚ Figure 17. AN1088 APPLICATION NOTE

duce the RDSon and the device dissipation. Application ideas for the L6234 follow. Figure 21. Copper side.

0.69 Rx Cx

Figure 22. Constant frequency current control

Low Cost Application with Speed and Torque Control Loops. performances and accuracy of the speed loop are not required. toff of the PWM is fixed by Rx2 and Cx2. duced torque in order to regulate the speed at the desired value. tor speed. This constrain limits the system bandwidth and so limits the response time of the loop. In most cases 1/KG can be neglected. Figure 23. Complete three phase brushless motor application with speed and torque control.

curacy of +/-1% , the V5 and Vref mismatch of +/-1% . is 400Hz. Therefore Ton has to be lower than 2.5ms (according to equation 1.1). Figure 24. 6x6 Three Phase Brushlees Application Circuit

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. Specification 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 © 2001 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 - U.S.A. http://www.st.com AN1088 APPLICATION NOTE