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FAN7093 Datasheet(PDF) 8 Page - Fairchild Semiconductor |
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FAN7093 Datasheet(HTML) 8 Page - Fairchild Semiconductor |
8 / 14 page © 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN7093 • Rev. 1.0.4 8 Protection Functions The device provides several integrated protection functions designed to prevent IC damage in fault conditions. Fault conditions are considered as “outside” the normal operating range. Protection functions are not for continuous or repetitive operation, with the exception of current-limit protection. In a fault condition, the FAN7093 applies the highest slew rate possible, independent of the connected slew rate resistor (RSR). Over-voltage, over-temperature, and over-current situations are indicated by a fault current flag IIS(LIM) at the IS pin. The following describes the protection functions in order of priority. Over-voltage protection overrides all other protections. Over-Voltage Protection (OVP) To ensure a high immunity against over-voltage conditions like load dump, the device turns off the low- side MOSFET and turns on the high-side MOSFET when the supply voltage exceeds the over-voltage protection level VOV(OFF). The control IC returns to normal operation tlock=140 µs (Typ.) after the supply voltage decreases below the over-voltage lockout level, VOV(ON). In H-bridge configurations, this behavior leads to freewheeling in the high side during over-voltage condition. If the load current exceeds ICP in over-voltage lockout, the IC turns off the high-side driver and latches this state. See Table 1, which shows the condition of the IS pin flag. This state can be reset (if the conditions no longer exist) when /INH goes from HIGH to LOW to HIGH again. Under-Voltage Protection (UVP) To avoid uncontrolled motion; for example, a driven motor at low voltages; the control IC turns off all MOSFETS when the supply voltage drops below the turn-off voltage, VUV(OFF). The control IC resumes to normal operation when the supply voltage rises above the turn-on voltage VUV(ON). Notice that the IS pin does NOT flag this fault condition. Over-Temperature Protection (OTP) The FAN7093 is protected against over-temperature by an integrated temperature sensor in the control IC. Over-temperature protection turns off both output stages. This state is latched until the device is reset by a LOW signal with a minimum pulse length of treset at the /INH pin, assuming the control IC temperature decreased by at least the thermal hysteresis. Repetitive use of the over-temperature protection decreases product life. Current Limitation The current is measured in both MOSFETS. As soon as the current reaches the limit ICL, the low-side or high- side MOSFET is deactivated and the other MOSFET activated for tCLS. During that time, changes at the IN pin are ignored. The /INH pin can still be used to turn off both MOSFETs. After tCLS, the MOSFETS return to their initial setting. The error signal at the IS pin is reset after 2 x tCLS. Unintentional triggering of the current-limit circuitry through short current spikes (e.g. inflicted by EMI coming from a motor) is suppressed by an internal filter. Reaction delay of the filter circuitry affects the current limit level ICL, depending on slew rate of the load current dI/dt. Figure 5. Current Limitation Timing Diagram (Inductive Load) In combination with a typical inductive load, such as a motor, this results in a switched-mode current limitation. This method of limiting current has the advantage of greatly reduced power dissipation compared to driving the MOSFET in linear mode. Therefore, it is possible to use the current limitation for a short time without exceeding the maximum allowed junction temperature (e.g. for limiting the inrush current during motor startup). However, regular use of the current limitation is only allowed as long as the specified maximum junction temperature is not exceeded. Exceeding this temperature reduces the life of the device. Short-Circuit Protection (SCP) The device is short-circuit protected against: Output Shorted to Ground Output Shorted to Battery Voltage Short-Circuit between the Load Connections The short-circuit protection is a combination of current limit and over-temperature shutdown of the device. |
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