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VN920SOTR-E Datasheet(PDF) 8 Page - STMicroelectronics |
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VN920SOTR-E Datasheet(HTML) 8 Page - STMicroelectronics |
8 / 23 page 8/23 VN920 / VN920-B5 / VN920SO GND PROTECTION NETWORK AGAINST REVERSE BATTERY Solution 1: Resistor in the ground line (RGND only). This can be used with any type of load. The following is an indication on how to dimension the RGND resistor. 1) RGND ≤ 600mV / (IS(on)max). 2) RGND ≥ (−VCC) / (-IGND) where -IGND is the DC reverse ground pin current and can be found in the absolute maximum rating section of the device’s datasheet. Power Dissipation in RGND (when VCC<0: during reverse battery situations) is: PD= (-VCC) 2/R GND This resistor can be shared amongst several different HSD. Please note that the value of this resistor should be calculated with formula (1) where IS(on)max becomes the sum of the maximum on-state currents of the different devices. Please note that if the microprocessor ground is not common with the device ground then the RGND will produce a shift (IS(on)max * RGND) in the input thresholds and the status output values. This shift will vary depending on how many devices are ON in the case of several high side drivers sharing the same RGND. If the calculated power dissipation leads to a large resistor or several devices have to share the same resistor then the ST suggests to utilize Solution 2 (see below). Solution 2: A diode (DGND) in the ground line. A resistor (RGND=1kΩ) should be inserted in parallel to DGND if the device will be driving an inductive load. This small signal diode can be safely shared amongst several different HSD. Also in this case, the presence of the ground network will produce a shift ( j600mV) in the input threshold and the status output values if the microprocessor ground is not common with the device ground. This shift will not vary if more than one HSD shares the same diode/resistor network. LOAD DUMP PROTECTION Dld is necessary (Voltage Transient Suppressor) if the load dump peak voltage exceeds VCC max DC rating. The same applies if the device will be subject to transients on the VCC line that are greater than the ones shown in the ISO T/R 7637/1 table. µC I/Os PROTECTION: If a ground protection network is used and negative transients are present on the VCC line, the control pins will be pulled negative. ST suggests to insert a resistor (Rprot) in line to prevent the µC I/Os pins to latch-up. The value of these resistors is a compromise between the leakage current of µC and the current required by the HSD I/Os (Input levels compatibility) with the latch-up limit of µC I/Os. -VCCpeak/Ilatchup ≤ Rprot ≤ (VOHµC-VIH-VGND) / IIHmax Calculation example: For VCCpeak= - 100V and Ilatchup ≥ 20mA; VOHµC ≥ 4.5V 5k Ω ≤ R prot ≤ 65kΩ. Recommended Rprot value is 10kΩ. 1 APPLICATION SCHEMATIC VCC GND OUTPUT DGND RGND Dld µC +5V Rprot VGND INPUT CURRENT SENSE RSENSE Rprot |
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