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H-Bridge-Slide9

This slide shows practically the same block diagram as slide 8 as this device is quite similar (virtually identical on the inside). There is one exception, however, which is that this device comes with the ability to add an external MOSFET for reverse battery protection. Looking at a reverse battery application, the ground becomes battery, and the battery becomes a ground. These two diodes (in the H-bridge) look like a short to ground in a reverse battery application, which could be a bad situation due to the high current. This device has the ability to insert an extra MOSFET externally to the device; essentially in the supply. Notice this MOSFET is in backwards. The diode faces the load, so in a reverse battery application this MOSFET turns off. There is no current flow out through to the battery. Designers should know not to rely on this if they want to do negative transients. It will not turn off fast enough to support negative transient suppression. A blocking diode would need to be utilized for that. This is a 19mOhm/leg device. Again, 30A is the minimum current limit. To reiterate, it is not what the device can handle, unless it is submerged in liquid nitrogen or something of that nature. It has the same sort of features as before, but now ST added something called an active power limitation. On the high-side switches they have implemented the M0-5 technology-type protections. This is a dual-stage current limit with an active power limitation. This has the same low-side PWM issues, the reverse recovery time and capacitance issue with the gates on the high-side drivers. So designers are limited to lower the speed or to keep the voltage down. This device works to 24V. This device has the current sense capability. The current sense in the M0-5 is much more accurate than in the M0-3. A limit to the technology is that at lower current levels, the less accurate it can be. MOSFETs like to share current only when currents are high. Because of this the current sense feature does not work quite as well at less than an Amp.

PTM Published on: 2014-12-19